Quickie Questions - Physics - Other

Date Answered Questioner (age, location) Question Answer
March 20, 2011keon(canada)how many much energy in watts do you produce per foot step?An adult human metabolism burns about 100 watts = 100 joules/sec. About 22% of that power is converted into mechanical energy, so lets say roughly 20 watts are produced while walking. A foot step takes maybe 0.5 sec of time. So I think the answer is 10 joules per foot step.
February 21, 2011George(New York)What is the difference between dark matter and dark energy?Matter and energy are equivalent in the sense that either can be converted into the other, such that the total matter plus energy in the universe, M, never changes. "Dark energy" is a hypothetical energy whose existence would help explain the observed accelerating expansion of the universe. Dark energy is about 73% of M, but only 1 gram in a cube 50,000 kilometers wide. "Dark matter" is also inferred to exist to explain cosmological observations, but is about 23% of M, and more variable in density than is dark energy. Both things are called "dark" because only gravity can "see" them, not light or any other forces. [Sources: Wikipedia and recalled lectures.]
May 3, 2010Humawhat is an electro-magnactic spectrum?The electromagnetic spectrum is defined as the broad range of wavelengths of radiation extending from very short wavelength cosmic rays to the very long wavelength radio waves, and travel through a vacuum at the speed of light. The visible light for humans is just a small fraction of the spectrum.
April 26, 2010ASIF (pakistan)I want to ask why everybody thinks STRING THEORY is correct,Is there any other approach to consider, to unify these four forces?Not everyone. The String Theory is still under a heated discussion among the theoretical physicists. Visit this forum for a taste of the discussion.
April 21, 2010carl (england)if i have the weight of a object and know the speed per min how do i work out the newton force on the groundFrom your question it seems the object in question is free falling under the attraction of the gravitational field, and the value of the acceleration (rate of change of the velocity) is given (in our planet, at sea level, it is g = 9.8 m/s2). Using Conservation of energy and assuming the object started moving from rest: Potential energy at the highest point P = mgh, (mass times acceleration of gravity times height), while kinetic energy K = ½ m v2 (1/2 mass times velocity square) = 0 At the instant before the impact, P = 0 (because h = 0), and K = ½ m V2, which means that all the potential energy was converted to kinetic energy. So, Initial P = Final K, or mgh = ½ m V2 From here, the final or impact velocity just before the impact Vf = square root(2gh). Now, from the work-energy theorem, work = force times distance = change of kinetic energy, W = F.d = ½ m Vf2 - ½ m Vi2, but Vi = 0 , then, Fimpact = (½ m Vf2)/d
April 20, 2010Albie (India)where does electricity come from?In the most simple definition, electricity is just the motion or flow of charged particles (of which all substances are made of) between two points.
March 30, 2010mauricio (mexico, sinaloa)caracterisar el conseptode precion. interpretarlo con el punto de viste microscopico y dar algunos valores caracteriticos.En física y disciplinas afines, la presión es una magnitud física que mide la fuerza por unidad de superficie. Por ejemplo,la presión atmosférica al nivel del mar, la fuerza por unidad de área debida al peso de la atmósfera, es de 760 mmHg o 101300 pascales (101.3 kPa).
March 30, 2010mauricio (mexico, sinaloa)explicar el origen de la fluides y gasesUn fluido es una sustancia que esta en estado líquido, gaseoso, o plasma, y que debido a su poca cohesión intermolecular, carece de forma propia y adopta la forma del recipiente que lo contiene.
March 24, 2010esso (france)what's the zero-gravity point between earth and moon?There are five points, known as Lagragian points, were the net acceleration (or net force) of an object is zero. The L1 point, which lies between Earth and the Moon, is at about 321.700 km from the center of gravity of the Earth-Moon system. See this document that describes the calculation of each Lagragian point for the earth-Moon system.
March 24, 2010Swati (India)Why is Pressure not a vector quantity??There are quantities that can be defined with just a number (or magnitude). For example, mass and pressure are independent of any direction, and will suffice to express then just with a number. These quantitues are called "scalars". There are other quantites that require magnitude and direction to be defined. For example, velocity and acceleration can't be fully defined without defining their direction (gravity, for example, is always directed toward the center of the earth). They are vectorials.
February 22, 2010Rashmi (India)what is the force experienced by a neutron when it moves in a uniform magnetic field?The answer to your question is a complex one. It has been known that a particle with a magnetic dipole (such as a neutron) undergoes an acceleration in an inhomogeneous magnetic field. But more recently it has been shown that a magnetic dipole in homogeneous magnetic and electric fields must undergo an acceleration both classically andquantum mechanically. See this paper for more detail (it handles high level physics).
February 9, 2010george (florida)If our universe only had one parcel of mass, how would it's speed be measured?Speed (scalar) or velocity (vector) need of a reference frame to be defined. In your hypothetical case, the only reference frame is that unique parcel, then, for any observer on it, there won't be any change of position, or v = 0.
February 5, 2010Deanna (Michigan)What does m/s2 mean?This is the unit used to express acceleration. Acceleration is defined as the rate of change of velocity. Because the unit of velocity is meter/second (or m/s) and time is expressed in seconds, then acceleration is expressed as (m/s)/s or m/s2.
February 4, 2010Kirsten (United Kingdom)Can you please help me identify examples of physical reactons and chemical? Please! You're the best!!Two of the most common are: 2H2 + O2 ¨ 2H2O (Hydrogen and Oxygen react to form water) CH4 + O2 ¨ CO2 + 2H2O (When a gas stove is lighted, methane reacts with the oxygen in the air, resulting in carbon dioxide and water vapor, and, of course, light and heat that you see as the flame).
February 3, 2010nisha (india)if i weigh the mass of a solid sphere at different place(ie;india,usa,germany etc........),would it be equal?If you are measuring the weight using an extremely accurate instrument, you would surely obtain slight changes on the measured weight, depending on your geographical location and altitud.
February 3, 2010kim (phillipines)why do objects move?Since Newton's time (4 January 1643 – 31 March 1727) it has been known that the cause of the motion of a body is an external force applied on it.
February 3, 2010David (Australia, NSW)In Bernoulli's principle, it says that in an incompressible, inviscid liquid, a increase in velocity (i.e. kinetic energy) is accompanied by a decrease in fluid pressure and potential energy of the liquid.
What kind of potential energy is this? Gravitational? Or is it an internal energy of some sort? I can't find this anywhere... Thanks!!
Potential energy is always related with the relative positions of parts of a system. In this case, it is energy stored within the fluid as a result of the position or configuration of the different parts of that system.
February 1, 2010Devinder (India)In String theory,what are strings made of?The strings of string theory are one-dimensional oscillating theoretical lines.
January 27, 2010Nikki (colorado)What experiments have led scientists to describe the shapes of orbitals that compose the atomic sublevels?The experiments with cathode-ray tubes, oil drop experiments, Rutherford's á-particle experiments, Moseley's X-ray experiment, and Chadwick's bombardment of 9Be with á-particles, were all very important for the definition of the modern atomic structure.
January 27, 2010SHIVAM (INDIA)How to decide the poles of a magnet kept in space?The same way we can identify poles on earth,following the lines of force of the magnetic field. The lines always come out of the north magnetic pole, and go into the south magnetic pole. They can be observed through the interactions with the solar wind.
January 15, 2010Alexey (USA)What fourth dimmension look like?This is a hard one! Better than to try to explain a fourth-dimension space, I will let one of the best science promoters, Dr Carl Sagan, do it. See here.
January 11, 2010Mary (USA)What is the effect of chemical weathering on a rock? phyical weathering?The processes involved in chemical weathering are CARBONATION (dissolved carbon dioxide in rainwater or moisture in surrounding air forms carbonic acid and reacts with the minerals in the rock); HYDROLYSIS (chemical reaction between the minerals in the rock and hydrogen in rain water); OXIDATION (oxygen combine with water and minerals in the rock forming iron oxide. The iron-oxide crust crumbles easily and weakens the rock); SOLUTION (minerals in the rocks dissolve directly in water); and HYDRATION (minerals in the rock absorb water and expand, creating stress which causes the disintegration of rocks).
January 11, 2010Richard (Colorado/United States)Why does your soft-drink can "sweat" more in the summer and than in the winter?Because warm air, due to its higher energy, "hold more moisture" (it is better to say that it is a more conducive environment) for gaseous water than cold air. When warm air is in contact with a cold surface, like a bottle of soft-drink, there is more moisture to condence.
January 8, 2010 If gravity were to completely disappear from the universe would the universe reach its maximum entropy as a result of that?This is a question better answered by a expert in Cosmology, but here are my two cents: I don't believe that this hypothetical condition (an Universe with no gravity) will imply a maximum entropy condition. There is still the kinetic energy of the system available for work.
January 7, 2010jj (us)what are the properties of plasma?From our web page The Plasma State: Almost everything is made up of atoms (your dog, your science book, this computer...). The atom has a nucleus which has a positive charge. Electrons orbit the nucleus. The electrons (which have a negative charge) are attracted to the nucleus. Remember, opposites attract! But sometimes something comes along that sets the electrons free from orbiting the nucleus. Really hot temperatures can do this! When electrons are no longer trapped in orbits around the nucleus, we have the plasma state.
December 30, 2009Nthabiseng (South Africa)Is water a pure element or a compound?The water molecule is formed by two atoms of hydrogen and one of oxygen, it is a compound.
December 30, 2009Nthabiseng (South Africa)Why does ice float on water?Because ice has lower density than water. Visit our Density Definition Page for more information on this property of matter.
December 30, 2009Balakrishna (Andhrapradesh/India)why inseries resisters voltage is split?This is related with the calculation of total resistance and the Ohm's Law. Resistances coupled in series are simply added (Rt = R1 + R2), the reciprocal of the net resistance from resistances coupled in parallel is the addition of the reciprocal of the values of the resistances(1/Rt = 1/R1 + 1/R2). Note that the combined resistance in parallel will always be less than any of the individual resistances. From Ohm's Law V = I*R (volts = amperes*ohms), voltage is proportional to the net resistance.
December 28, 2009steve (calif)Hi, an opportunity might present itself to use a community hiking trail to mark planetary distances along the trail, measured from a model sun at the trailhead. A brochure would compare how the sun and planets interact to make differing conditions in temperature, atmosphere, etc., all to better appreciate ecology, too. In marking planetary distances from a 50 inch sun circle, it became apparent that the location of planetary semi-major axis and peri- / ap-helions on the trail would differ by a sun radius depending on whether planetary distances are measured from the sun's surface or center. The Sun's radius of 435,000 [ 0.7 million km ] is within significant numbers for planetary distances and would also affect our model planets by 2 feet. It would nice to know for closer terrestrial planets. Is triangulation to the Sun's surface, or its center? Thank you for any light to us on the subject. Astronomical distances are usually measured to the center of the bodies, and it is the case with distances in our system.
December 22, 2009Eric (Indiana/USA)How long would it take to go 9.461 light years ?1 light year is the distance the light will cover traveling in a vacuum in a year (9 460 528 400 000 kilometers or 5,878,499,810,000 miles). So, to cover 9.461 light years the light needs 9.461 years.
December 22, 2009anne (philippines)in the thermosphere, the temperature of an orbiting spaceship is determined by the amount of solar radiation it absorbs and not the temperature of surrounding air. if an astronaut extends his arms out his spaceship will his arm be burned? why? (the temperature in the ionosphere is 1000 degree celcius.)Due to the very low concentration of particles, temperature at these altitudes describe the kinetic energy of the molecules in the medium rather than the "heat feeling" that we are used to.
December 16, 2009Alberto (Puerto Rico)What if I were on a cement platform that fell from a big building and I jumped up before the cement platform smashes on the ground?What will happen to me?Let's make a simple calculation. Any object in a free fall moves with a downward acceleration of 9.8 m/s2. That means that the vertical velocity of the object increases in 9.8 m/s (32.2 ft/s) each second. In ten seconds of free fall, the object will be moving at 98 m/s (321.5 ft/s), at 100 sec, it would be 980 m/s ( 3 215.2 ft/s). To cancel out this downward motion, you would have to jump up with a initial speed similar to these values!
October 27, 2009sreeragh (kerala/india)i heard that every object on earth is attracted towards the centre of earth, if there is no conductor for this attraction why it is telling the man in a vaccant box will fly, since he is also in the earth's magnetic field, with weight. is there any conductor for magnetic field in the air?A magnetic field doesn't require of a conductor to exist, it exists between two magnetic poles.
October 16, 2009sean (WA)what is dark energyDark energy is a hypothetical form of energy that permeates all of space and tends to increase the rate of expansion of the universe. Along dark matter they form about 75% of the matter/energy of the universe.
October 16, 2009Ashvin (Nepal)what does the electron revolves round the nucleus?In classical physics, the electron rotates around the nucleus following the Bohr "planetary model". In quantum physics, the electron does NOT rotate around the nucleus, is not just an electron any longer but instead a wave.
October 16, 2009Ashvin (Nepal)if two cars with no mass are going in the speed of light in the vaccum and the car at the back turns the headlight will it be able to see the car infront?(imagination)Forma purely physics point of view, this question does not make sense. But assuming room for a lot of assumptions, no, the front car won't be able to see the lights from the following car.
October 16, 2009Ashvin (Nepal)If we strike ball on the wall then does it returns on the same speed as we throw it or not ?if not why ? does the wall obsorb the energy of the ball ? if yes then how?In an ideal case, frequently used in introductory physics to teach the basic principles of the mechanical interaction between two bodies, there is no energy lost (it is called a perfectly elastic interaction), but this is not the case in real interactions, where there is an energy transfer between the bodies. This is the cause for a lower returning speed.
October 8, 2009RONALD (VENEZUELA)HOW CAN YOU CALCULATE THE EARTH GRAVITY (9,81 m/s2)? HAVE YOU A FORMULA? STILL TODAY IT'S ONLY A MEDITION...There are many ways to do it. The one I like, and have used in the past with my students, is using a pendulum. The period of a pendulum is given by a simple expression ( T = 2Ð (l/g)0.5 ), where T is the period of the pendulum (a full oscilation), l is the lenght of the pendulum string (should be aslong as possible), Ð = pi = 3.14159265, ang g is the acceleration of a free falling object (due to gravity). It is very easy to measure T, and from this expression to obtain g.
October 8, 2009katelin (geelong)when a substance is heated its tempreture increases, what other change might be observed?Many changes occur when a substance is heated. With the increased temperature, the atoms and molecules move faster and in a less organized fashion, the dimensions of the object change, increasing both its linear dimensions and its volume. If we continue heating the substance it could reach the melting point, when a solid becomes a liquid.
October 2, 2009Stephanie (Florida/USA)The phase of matter when it reaches close to absolute zero kelvin through magnetism when all atoms become as 1. If it were possible that when atoms can reach that point would that explain a burst of energy on the opposite end of the spectrum transformed into a plasma/ or absolute heat. Everything in the universe is based off +/-, there are 2 sides to everything like a continues circle of perfection. saying there is always a neutral between the both +/-.There are two states of matter related to temperatures close to 0 K, superfluids and the Bose-Einstein condensate.
October 2, 2009Hammad (Pakistan)What is difference between electric and magnetic fieldIn the simplest possible way, there is an electric field in some region of space if electrically charged objects accelerate in a particular way, but electrically neutral objects do not. Similarly, there is a magnetic field in some region of space if objects with inherent magnetism rotate in a particular way, but objects without any inherent magnetism do not. See this article for more information.
October 2, 2009karthikeya (india)why do clouds appear in different shades of yellow and red during the time of sunset?The red colour at sunset (and sunrise) is due to an effect called Rayleigh scattering. At this time, the distance that the light has to travel to an oberver is longer, and a larger amount of blue and violet is scattered, the remanent, a longer wavelength, corresponds to red.
September 30, 2009courtney (New Zealand)Mercury is an element that is a liquid at room temerature. It is used in thermomerters to measure how hot or cold a substance is. Explain what happens to the mercury in a thermometer when it is taken out of hot liquid and placed into a cold liquid.All substances change with change in temperature (and pressure, and volume). When temperature increase there is a increasing in the volume of the mercury, and viceversa, with a decreasing temperature, the volume also decrease.
September 28, 2009Jameela (Michigan/United States of America)What happens when rays of light incident on a lens and parallel to the principal axis of the lens converge?They cross a common point known as the focus of the lense. This is the principle for parabolic antennas.
September 17, 2009Liza (Philippines)What happens when a bar magnet is heated to a vey high temperature?thank uThere could be a random realigment of the atoms, resulting in a weakened magnetic field, or a magnetic field destroyed by this random realigment.
September 17, 2009Lily (Philippines)is a hydrogen atom a magnetic dipole?why?A hydrogen atom contains a single positively-charged proton and a single negatively-charged electron or, in other words, two equal and opposite charges ±Q separated by a distance s. The definition of electric dipole.
September 17, 2009safia (india)when do we say an electric diople is ideal one?An electric dipole consists of two equal and opposite charges ±Q separated by a distance s. In an ideal dipole s is very small compared to the distances to any other charges and also to any points where we wish to find the resultant electric potential or E-field. However Q is sufficiently large such that the product Qs is finite.
September 17, 2009Nathan (USA)I've been told by my physics professors that atoms can have an instantaneous connection with one another, regardless of distance. If this is so, wouldn't that "connection" be faster than any speed, including light?This is still a topic under discussion. For example, the scientific paper Nonlocality and Casuality in Quantum Electrodynamics, by Compagno and others (published in The Physics of Communication, Proceedings of the XXII Solvay Conference on Physics) debate the topic, concluding that "Our method... allows an unambiguous identification of which contribution to the evolution of one atom comes from the other..." In other words, no instantaneous connection.
September 16, 2009jessica (nd)the acceleration of gravity on the surface of Mars is 37m/s^2. if an astronaut in a space suit can jump upward 20 cm on earth's surface, how high could he jump on the surface of Mars?From the simple kinematic expression: Vf2 = Vi2 + 2gh where: Vf - Final speed (which is zero for the maximum height), Vi - Initial speed (assumed to be the same in both cases), g - acceleration of gravity for Earth (gE = 9.8 m/s2) and for Mars (gM = 3.7 m/s2), and h - height reached at each planet (hE = 20 cm). Because the final speed is zero, Vi2 + 2gEhE = Vi2 + 2gMhM Because the initial speed is the same, we get, gEhE = gMhM From where: hM / hE = gE / gM Or hM = hE * gE / gM And using the numerical values we obtain that hM = 53 cm.
August 26, 2009Marcus (Singapore)Why is space without air?Because air molecules, since they have mass (= 5.6 x 10-26 kg), are under the gravitational pull of the planet.
August 19, 2009cya (india)why are bubbles always spherical in shape?The walls of the soap bubble behaves as an elastic membrane under tension (known as surface tension). Under this tension, the membrane tends to become as small as possible, and since spherical shape has the least surface among all shapes, the bubbles tend to become spherical.
August 12, 2009Narayanan (Kerala,India)It is said that ,from the beginning ,universe has been expanding due to the conversion of dark matter to dark energy. If so, what is the force causing it?This is a very controversial topic, where no final theory has been produced and accepted by the majority of the scientists. Our web pages The Future of the Universe and An Eternal Universe offer general information on this issue.
July 22, 2009Catherine (Mo/USA)If the temperature graph of a certain experiment formed a straight line when recorded on the Celsius scale, what would a graph of the same experiment on the Kelvin scale look like?Consider the following values in Celsius (0, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100). The corresponding values in the Kelvin scale are (273.15, 283.15, 293.15, 303.15, 313.15, 323.15, 333.15, 343.15, 353.15, 363.15, 373.15). Both series form a straight line.
July 16, 2009NIraj (Assam/India)what makes a string Oscillate in a frequency
is there any forces behind it?
For the oscilation to continue there should be forces acting. Once the spring is compressed by an external force, it tends to recover its original lenght under the action of an internal force known as elastic force.
June 17, 2009Bryce (Colorado)In string theory, gravitons are used to explain gravity. How do gravitons explain gravity on the quantum level?An important thing to keep in mind is that the graviton is a hypothetical elementary particle that mediates the force of gravity in the framework of quantum field theory. However, attempts to extend the Standard Model with gravitons have run into serious theoretical difficulties at high energies because of infinities arising due to quantum effects. More information here.
June 16, 2009CAROLYN (NJ)What are the four components of the water molecule. So far, I have three, including 2 hydrogens and 1 oxygen. Where in the model or diagram shown is the 4th component?Could you send the http addres of the model or diagram shown? As you pointed out, the water molecule is made of two atoms of hydrogens and 1 of oxygen. I don't know of any other element.
June 2, 2009Cariel (New Jersey, U.S.A.)How many Elements are on the Periodic Table of Elements?The Periodic Table of Elements currently has 113 elements.
June 2, 2009chances (usa)what is the chemical reaction formula for rustingThere are different reactions that can be described as rusting, all of them involving oxygen in any of its forms.
May 18, 2009Narayanan (INDIA)How dark matter & dark energy is related to the expansion of universe?In physical cosmology and astronomy, dark energy is a hypothetical form of energy that permeates all of space and tends to increase the rate of expansion of the universe. Dark matter, on the other hand, is hypothetical matter undetectable by its emitted radiation, but whose presence can be inferred from gravitational effects on visible matter.
April 28, 2009aakanksha (india)how is ozone related to oxygen?The oxygen molecule is formed by two atoms of oxygen (O2), ozone is formed by three atoms of oxygen (O3).
March 10, 2009Bianca (Philipppines)What are phyisical quantities?Physical quantities are jusies physical property that can be quantified (measured and/or calculated and expressed in numbers.)
March 3, 2009cya (india)can you please explain me about despersion and bending of light?Refraction is the bending of light rays as they pass through the interface between two transparent media. This is caused by the different speed that different wavelengths have in a medium.
March 2, 2009Mike (Tx)If 2 trucks are going the same speed on level ground, one has a load of 40,000 lbs the other is empty, which truck requires more energy to maintain momentum, and would this be the same if it were 2 oil tankers, one full one empty and would the answer be the same if we assumed that there was no friction in either caseLet me try to answer: Momentum = mass * velocity. Change of Momentum = Energy. So, the loaded truck will have a higher value of momentum, but if this value is constant, then there is no energy being used. Of course, this is assuming ideal conditions. There are factors like friction that complicate the picture. When these factors are considered, there are other expression to use. The friction produces a de-acceleration of the bodies, and a constant force (of the same value of friction, but opposite) has to be applied. The coefficient of friction is proportional to the mass, then a higher friction will act against the motion of the heavier object, and a higher force will be required to keep the motion.
February 27, 2009Vidya (Bangalore, India)how do you know that when you pass by the event horizon of the black hole the time slows down as no one has even gone near a black hole ?Physicists, using the models most currently accepted, theorize about systems that they can't visit, including black holes. Their theories are based on previous theories tested by the scientific community, and they will be tested against new observations and experiments.
February 24, 2009Yonatan (Israel)Why isn't there ice on the ocean floor?
No radiation gets there, so how come the temperature there is 3 degrees and not below zero?
Fluids, like liquids and water, tend to circulate trying to balance the temperature everywhere. These so-called circulatio cells move energy from hot to cold spots.
February 10, 2009emy (cairo)pllzzzzzzzzzz can u tell mee more about the plazma state ? thnx for reading my questionPlasma is known as the fourth state of matter. Really hot temperatures can set the electrons free from orbiting the nucleus of atoms. When electrons are no longer trapped in orbits around the nucleus, we have the plasma state. Most of the matter in the universe is found in the plasma state.
February 9, 2009Saurav (Bihar state)What is Plasma state of matter? Where can i see it? Is this visible or not?Plasma is known as the fourth state of matter. Really hot temperatures can set the electrons free from orbiting the nucleus of atoms. When electrons are no longer trapped in orbits around the nucleus, we have the plasma state. Most of the matter in the universe is found in the plasma state.
February 8, 2009kenneth (UNITED STATES)ON THIS SIDE OF THE UNIVERSE IF A STAR WAS TO EXPLODE WOULD THE SOUND OF THE EXPLOSION CARRY ON WITHOUT DIEING OUT BECAUSE THERE WILL NOT BE ANY FORCE THAT WOULD CARRY INTO A the sound into a fracture of sound I mean like there will not be any opposing force to have it die down. EXPLOSIVEThe sound is a mechanic wave that NEED a medium to propagate. There is no sound transmited in a vacuum.
February 5, 2009Rabia (Pakistan)what does it meant by forming the image infront or behind the plane mirror?Although a plane mirror makes images of the objects in front of it; these images appear to be behind the plane in which the mirror lies. In the case of plane mirrors, the image is said to be a virtual image (images formed in locations where light does not actually reach).
February 2, 2009ofelia (PENNSYLVANIA)what happens to a substance when it goes through a physical change?Physical changes between the states of matter can be produced by heating and cooling. The heat being added or substracted increases or decreases the vibration (motion) of atoms and molecules. This changes the way in which the molecules and atoms interact. For higher temperatures the molecules and atoms will have more motion, will be farther from each other, and will interact less (which corresponds to liquids and gasses), for lower temperatures the opposite happens: less vibrational motion, closer to each other, more intense interaction. This corresponds to solids.
February 2, 2009rajendra (lndore(MP))what actual difference between classical mechanics and quantum mechanics ?Quantum mechanics is the branch of quantum physics that accounts for matter at the atomic level; an extension of statistical mechanics based on quantum theory (from wordnet.princeton.edu/). Clasical mechanics only deals with the motions of macroscopic objects.
January 28, 2009Ella (Minnesota)Is light a gas,a liquid,or a solid?Light is an electromagnetic radiation that has a dual behaviour as a wave and a particle.
January 27, 2009Gus (Washington)how fast is sunlightThe speed of light in a vacuum is 299 792 458 m/s.
January 22, 2009Ashuntae (South Carolina)What is a convection current? I've got to know this for my project on the atmosphere before tomorrow because we're working on a childrn's book in science class.The movement of heat through any fluids (liquids and gases). When the substance is heated from below, the liquid or gas will expand, become less dense, and rise. When it is away from the source of heat, the opposite will occur, the liquid or gas will contract and sink.
January 20, 2009ROGER (NM )DOES STAR AGE SUPPORT BIGBANG THEORYThe age of stars varies in a wide range, as it should be due to the life cycle of a star. As far as I know, the age of stars has not been use to support nor against the BB theory.
November 12, 2008jake (md united states)how can you relate newtons third law to locomotivesAll bodies moving at much lower speed than the speed of light follow Newton's Three Laws of Mechanics. The third law applies to a locomotive in that it allows the motion to happen. When the train wheels start to move, the contact point with the rails is moving in the opposite direction, and there is an equal and opposite force of the rails on the wheels. This par of forces (known as action-reaction forces) act simultaneously, and are the cause of the motion of the locomotive.
November 6, 2008Kylee (United States)What is kepler's 2nd law?Kepler's second law of the planetary motion: The line joining the planet to the Sun sweeps out equal areas in equal intervals of time. As a result of this law the planets move faster when they are closer to the Sun.
November 4, 2008bernadette (united kingdom)how many meters are there in 12 billion light years12 billion light years = 1.13526341 × 1026 meters
November 3, 2008Howard (Canada)Can earth provide anymore energy resources such as fossil fuel?The existence of fossil fuels are limited. They are non-renewable sources of energy. We should, sooner rather than later, start producing energy from renewable sources like the Sun, wind, etc.
November 3, 2008Liz (England)What would happen to the temperature of a 1Kg block of Al at 50 degrees C if it was dropped into 1Kg of water at 20 degrees C?There would be an increase in the temperature of the water, and a decrease in the temperature of the Al. If there is no transfer of heat to the recepient or the surroundings, then the following relation -mAlcAl(T-TAl) = mWcW(T-TW) where m (mass), c (specific heat), T (equilibrium temperature), TAl (temperature of the Al block), TW (temperature of water); should be satisfied.
November 3, 2008Maria (Kansas/USA)Which of the following is not a change from liquid to gas states.
a. vaporization b. boiling c. condensation d. evaporation
Condensation is the process of changing from a gaseous to a liquid state.
October 22, 2008kerianne (ohio/usa)what form of measurement to scientist useMany, many types of measurements are used by scientists. Scientist need to measure simple magnitudes as mass, weight, height to more complex like force, electric and magnetic field, plasma concentration and energy. There are many other magnitudes but the list would be too long to compile.
October 21, 2008Dequisha (New York, United States of America)is it true that scientist seen atoms or is it a theory. If it is why would they say copper is made of atoms if they don't even know if it exists. My science book is exploring creation with physical science written by dr. jay l. wile. so please answer my question so i can understand itSee by yourself this picture, or this one.
October 21, 2008sumaita (india)how does the astronauts receives messages from the earth when they are in the space since we know that the soundwaves cannot travel through vacuum but there is no air in space?You are right on that soundwaves cannot travel in space. They are mechanic waves, that require a medium to move. However, radio signals are electromagnetic waves, that do not require a medium for propagation.
October 16, 2008Colin (Ontario/ Canada)What determines that an electron will have a negative charge, a proton will have a positive charge, and a neutron will have no charge?As you said, electrons have negative charge, and protons have positive charge. The terms "positive" and "negative" are arbitrary. The essential implication of that is that the proton and electron will strongly attract each other, therefore they have opposite charges.
October 3, 2008Uri (Israel)I'm 59 years old and amateur cosmologist for the last 30 years.
I have a question on Linear Chirp (http://en.wikipedia.org/wiki/Chirped_radar) energy.
The energy of electromagnetic radiation is given by E=hf.
What is the equation for the energy (instantaneous) of Linear Chirp wave?
The instantaneous frequency of a linear chip radar varies in time following the expression f(t) = fo + kt. The energy at any given time will then be expressed as E(t)= hf(t) = h(fo + kt).
October 1, 2008patti (ohio)why is measurement a better means of describing something to a scientist than just using qualitative observation and our senses?Because scientists around the world use, in most the cases, the same measurement systems, which is void of any personal (subjective) element. In this way we can "talk" to each other using the same terms!
October 1, 2008Yadira (INDIANA)How is it possible for you to hard math??(6.67 × 10−11 N m2 kg−2)The first part (6.67 × 10−11) just means a number preceded by eleven zeros: 0.0000000000667. The second part (N m2 kg-2) is called units or dimensions of the previous number. This expressed what this number is about, in this particular case the number descibes how the gravitational force (expressed in N = Newtons, units of force) varies with the distance (m = meters) and the mass (kg = kilogram).
September 25, 2008 Can the way that solar panels convert light into electricity be viewed as that the solar panels uses what does not change( what does not change refers to a constant, which in this case being the speed of light ) to replenish what does change, and what does change refers to what decreases, meaning the energy loss in the form of heat due to friction of 2 bodies( 2nd law of Thermodynamics )?I am not sure what your question is, but what a solar panel does is to transform the solar energy in to electric energy. There is a detailed description of the inner working of solar cells here.
September 24, 2008USMAN (PAKISTAN)WHAT IS A WEATHER FORECAST?Weather forecast is the prediction of future weather for a given location, based on the current conditions, weather patterns and the output of models developed by scientists.
September 8, 2008ayan (india)what is the reason(mechanism) of existence of "inertia"?There is no reason or mechanism for inertia, it is a general property of matter to tend to keep their state of motion or to tend to stay at rest.
September 3, 2008SUNNY (INDIA)WHAT ARE PROPERTIES OF PLASM STATE OF MATTER ?Plasma state is where a gas becomes a collection of negatively charged electrons which have escaped the pull of the nucleus and ions which are positively charged because they have lost one or more electrons. More information on our web page Plasma State.
September 1, 2008deepti (india)i need to know about curvature of spacePLease, visite This page for a detailed answer to your question.
September 1, 2008Zach (Nevada)Here in nevada we have many problems with high temp.
My question is is there any way to actually stop the heat from transfering to other objects, or does heat win every time?
There are many methods to slow down to a minimum the transfer of heat. But because the transfer of heat is just the transfer of kinetic energy from molecules, atoms and elemental particles to other, it is impossible to create the "perfect insulator".
August 29, 2008Thu (United Kingdom)Why does some liquids mix together while other does not?Actually, all liquids mix together, it just depends on the right amount of energy (heat, motion, etc) given to the system. For example, oil and vinegar do not mix under normal conditions, but it just requires a little shaking for them to mix. Other examples would require heating, or pressing, etc.
August 24, 2008jugal (west bengal, india)where else is the concept of density used in daily life ?Everywhere. density is a characteristic of all matter (mass/volume).
August 21, 2008Crystal (CA)The specific heat of water is 4.2 joules/g celc. If you wish to heat 300 grams of water from 30 degrees celc, how much heat will be required?The temperature to reach is necessary to answer your question.
August 21, 2008aheli Pul (India)What is the shape of a water bubble in space and why? In the Earth due to the gravity it is in the shape of a tesr drop. Does water evaporate in space. if it is so then where the evaporated water go.The espherical shape is the minimum energy shape. All bodies, in the absence of external forces, will tend to this shape.
August 21, 2008aheli Pul (India/jamshedpur)What is the shape of a water bubble in space and why? In the Earth due to the gravity it is in the shape of a tesr drop. Does water evaporate in space. if it is so then where the evaporated water go.The espherical shape is the minimum energy shape. All bodies, in the absence of external forces, will tend to this shape.
August 20, 2008Genevieve (Texas)he most common elements in the earths crust are rarely found on their own, they are usually found combined; why is this?Because chemical elements tend to react among them, forming new substances as a result.
August 14, 2008sharanya (karnataka,India)why is ligtning not caused when it is not raining?Actually it does. It is very common to observe lightining with no rain.
August 14, 2008sharanya (karnataka,India)Of course, water contains oxygen,why does not it help in burning?The hydrogen in the water molecule has already reacted with the oxygen. It is not available for further reaction with air, neccesary for burning.
July 1, 2008Michael (NSW,Australia)How much is a lightyear?1 lightyear = 9.4605284 × 1015 meters, which is the same as 9 460 528 400 000 000 meters, or 9 460 528 400 000 km, or 5 878 499 810 000 miles.
June 18, 2008Nathan (Texas)How many other dimensions are there? And how would they affect humans if we were in them?Physical theories have predicted for a long time the existence of other dimensions. So far there are no concrete proof in favor or against them.
June 17, 2008 if you hit a golf ball hard can it go out of the moons gravity pullAny object that can be accelerated up to a speed greater than the Escape Velocity (about 11.2 kilometers per second), will abandon our planet.
May 29, 2008anthony messere (haynnis ma)is the big rip dangerouse. should i be worried in this life time. pluss gamma rays scare me.I wouldn't worry too much. The authors of this cosmological hypothesis, in which the matter of the universe is progressively torn apart by the expansion of the universe, calculate that the end of the universe would be in approximately 50 billion years.
May 23, 2008Krista (Philippines)How do scientists measure each planets?atmosphere? or even the sun?Scientists use multiple methods to measure the celestial bodies and their distances. From parallax, used by Cassini in 1672 to measure the distance to Mars, to Issac Newton's Law of Universal Gravitation used to obtain the mass of the Sun and the planets, science is continuosly advancing our knowledge of the planets and other celestial bodies.
May 22, 2008Renae (Washington)How do scientists measure to find out how old rocks are?There are different methods (of diverse accuracy) to date rocks. One of the most used is radiocarbon dating. It uses the naturally occurring radioisotope carbon-14 (14C) to determine the age of carbonaceous materials up to about 60,000 years.
May 22, 2008brendan (pipersville PA)Could you please explain density to me? I am doing a liquids project for preschool
Density is a characteristic of each substance that represents the amount of mass in each volume unit. In other words, if we obtain the mass of an object (a weight scale can be used, although mass and weight are not exactly the same), and the volume of a liquid (or gas or solid), then we can divide the mass by the volume (density = mass/volume) to obtain the density. For example, ice has higher density than water, and this is the reason for ice to float!
May 7, 2008eloisa (philippines)are there any more example for sublimation aside from drying ice?Sublimation a transition from the solid to gas phase with no intermediate liquid stage. Sublimation, as any other phase change, depends of three factors, temperature, pressure and volume. Most substances would be able to sublime controlling these parameters. There are other compounds, besides dry ice, that sublime at atmosheric pressure. For example, ionide would sublime with a light heating and snow also sublime (slowly) at below-freezing temperatures.
May 2, 2008Chris (Florida, U.S.A.)If a device could be constructed that would allow you to travel to the center of the Earth, (it could get you there, protect your body, etc.) what sort of gravitational force as well as centrifugal force could you expect?The answer to this question is very complicated because the many different factors acting simultaneously. A detail answer must include factors such as radioactivity, temperature of the core, variations in density, rotational motion, etc. There is also the issue that the center of the earth is not exactly the gravitational center. For a simple, uniform solid sphere, with an empty center, the gravitational force would be cero in the center, but this is far from the real case of our planet.
April 30, 2008Cameron (Ohio/U.S)Why do solar cells produce more electricity in low temperatures?A detailed answer to your question is beyond this section, but you can find it here.
April 24, 2008 What kind of rock is halite: a sedimentary rock, an igneous rock, or a metamorphic rock?Halite occurs in beds of sedimentary minerals that result from the drying up of enclosed lakes, playas, and seas. Halite is the mineral form of NaCl, commonly known as rock salt.
April 24, 2008Sandira (Nassau,Bahamas)The weight of all layers of the atmosphere creates what type of force?The weight of all layers of the atmosphere on each square centimeter is called ATMOSPHERIC PRESSURE.
April 23, 2008Azfarihin (Singapore)With the earth rotating, revolving and hurtling through space at fantastic speeds, why can't we feel the movement?Why does everything appear to be motionless?The short answer is because we are moving WITH the earth at the same rate. It is like being in a car that moves at a constant speed on a smooth, long and straight highway, if we close our eyes we will not feel the motion, unless the car accelerates, turn or break.
April 18, 2008Alex (Minnesota/ USA)What is the KE of the Earth with respect to the sun as the sum of two terms, that is due to the daily rotation about its axis, (Assuming the the Earth is a perfect sphere, with a mass of 6.0*10 to the power 24 kg, and radius of 6400000 meters, and a distance from the sun 150000000 metersThe TOTAL kinetic energy of an object in motion is obtained by adding the translational term (Kt = 1/2 mV2, where m is the mass of the object and V its translational or lineal velocity) and the rotational term (Kr = 1/2 Iw2, where I = mr2, and w is the angular speed).
April 9, 2008chamisa (va)besides the stars what is another example of plasma?Lightning, the Sun, Nebulae, Solar Wind, Auroras, Quasars, Radiogalaxies, and Galaxies are all examples of the plasma state.
April 8, 2008MUENCH (US)WHAT PLANET DISCOVERED BY MATHEMATICS?Although Neptune was physically discovered on September 23, 1846 by the astronomer Johann Galle, is existence was predicted before by a young British astronomer and mathematician , John C. Adams, in 1843. The discovery of the asteroid belt is also a good example of how mathematic has helped the astromers.
April 8, 2008Jared (Iowa)As light travels through water, does the refraction index (and thus the speed) change as the temperature of the water changes?Absolutely, the relation between the refraction index (n) and temperature (T) expressed in Celsium is given by the expression: dn/dt = -0.0004 1/oC
March 31, 2008mary ann (philippines)why are the spetral lines of many stars shifted toward the red end of the spectrum?This effect, first described by Christian Doppler in 1842, relates the change on the frequency (in this case color) with the direction of the motion. The shift to red indicates that all celestial bodies are moving farther from each other.
March 25, 2008VARSHA (INDIA)WHY DOES THE PLANETS MOVE FASTER WHEN IT COMES NEAR TO THE SUN.?This is a result of the universal law of conservation of energy. A planet orbiting a star has two forms of energy, Kinetic Energy (K, energy associated with the speed of its motion) and Gravitational Potential Energy (P, energy associated with the gravitational attraction of the two objects). From these concepts it is straightforward that for greater distances between the star and the planet, the greater the potential energy will be. Now, from the law of conservation of energy, K + P = constant. So, when the planet is closer to the star, P is small, and, to conserve K+P constant, K, and the speed, should increase.
March 20, 2008Rachna (Toronto, Canada)what feature of clouds allows them to reflect the light and heat of sunlightIn general, light-colored objects reflect better heat and sunlight.
March 19, 2008Dustin (Ohio / USA)What is the advantage of radio waves?Radio waves are a form of electromagnetic radiation. Through them we can communicate all around the planet, with satellites, shuttles and the International Space Station. Scientists study the Sun and the Universe using radio telescopes. Our web page Radio Waves offers more information on this topic.
March 18, 2008Ksnake (Dubai/UAE)how does current follows the electric field intensity differences in a circuit ?The Electric Potential Difference, commonly known as "voltage", is define as the work needed to move a charge between two points. The direction of the electrons movement (electric current) is from the negative pole to the positive one, but by convention the positive sense of the current is from (+) to (-). It should be mentioned that the intensity of the electrical current is only a function of the resistance of the conductor.
March 17, 2008Mahima (india)how can earth take and give any number of electrons?Not only our planet, everything in the universe is constantly taking and giving away charged particles. This is part of the normal interaction at atomic level.
March 5, 2008JAMIE (NAUGATUCK)WHAT ARE NEWTONS THREE LAWS?First Law (Inertia): Every object in a state of uniform motion (or rest!) tends to remain in that state of motion unless an external force is applied to it. Second Law (Force): If a force F is applied on an object of mass m, it will acquire an acceleration a proportional to the force F (F = ma). Third Law (Action-Reaction): For every action there is an equal and opposite reaction.
February 15, 2008Denese (Tennessee)What are the three atoms that make up the ozone layer?A molecule of ozone is made up by three oxygen atoms.
February 11, 2008Ian (ON)You know how there are only two charges. Positive and negative. Their laws state that opposites attract and likes repel. Is there any way of changing the properties of charges.This is a basic principle of the interaction of charged particles. There is not, as far as I know, a way to change this interaction.
February 11, 2008Ian (Burlington ON)If neutrons have no charge then what is their purpose of the atom or do they do anything at all?Like the rest of the particles, neutrons do not need a purpose, they exist, they just are.
February 11, 2008Ian (ON)If neutrons have no charge then what is their purpose of the atom or do they do anything at all?Like the rest of the particles, neutros do not need a purpose, they exist, they just are.
February 11, 2008Ian (ON)Theoretically is it possible to heat something to a certain extent that the electric fields of the atoms would dissapate?When an atom is accelerated to a high velocity, the electric charges and the absolute electric field around those charges do not have to change in order to remain compatible with the principle of mass-energy conservation. More information here.
February 11, 2008AKuah (New Jersey)What ar the particles of matter?All matter is composed by molecules and atoms. The atom is composed by neutrons, protons and electrons, which are called elemental particles.
February 6, 2008Stephanie (California)If you are going 70mph straight in the freeway and you threw a baseball in the air, would it land in the same spot?From your point of view, assuming you are in the same auto, the ball will go straight up and down, and will land in your hands, but for somebody standing on the side of the road, the ball will follow a parabolic (ballistic) trajectory, at the same time that you are moving in a straight line. This observer will see, as you do, that the ball will land in your hands.
February 3, 2008Ian (ON)What is wave particle duality?In Physics, wave–particle duality is the concept that all matter exhibits both wave-like and particle-like properties.
February 3, 2008Ian (ON)What is quantum entanglement?The Standford Encyclopedia of Philosophy defines quantum entanglement as a physical resource, like energy, associated with the peculiar nonclassical correlations that are possible between separated quantum systems. This article discusses the topic in a very interesting way.
February 3, 2008Ian (ON)My physics teacher likes to rant about how when you touch something you are not actually touching it at all it's just the exchange of electrons. Is this true or is it different or am I right?In a macroscopic scale, the act of touching consist in bringing in contact our fingers and abother object. In microscopic physics "touch" can not be defined in the same way, the interaction of subatomic particles blurr the act of touching.
January 24, 2008Anudip (India)According to releativity theory Mass and Energy can be converted to each other, is it possible to convert any known mass to energy and energy again to mass? Can you explain me this phenomenon with example.The idea of the mass-energy equivalence as a general principle was proposed by Albert Einstein. His well known expression E = mc2 uses as the equivalence factor the square of the speed of light (299,792,458 m/s)2. Is due to this high value that the conversion between mass and energy is not easily observed at velocities much lower than the speed of light.
January 24, 2008Chiranjeev (India)How does a spacecraft flies in space where there is no air?Spacecrafts fly in space based on a physical principle known as "The Law of Momentum Conservation". Momentum is defined as mass times velocity P = m V). This principle states the in the absence of a net external force, the net momentum of a system remains constant (dp = 0), so, if the mass of a system decreases, the speed will increase. After a given speed is reached the ship will continue its motion due to the inertia.
January 24, 2008Chiranjeev (India)How does a spacecraft flies in space where there is no air?Spacecrafts fly in space based on a physical principle known as "The Law of Momentum Conservation". Momentum is defined as mass times velocity P = m V). This principle states the the net momentum of a system remains constant (dp = 0), so, if the mass of a system decreases, the speed will increase. After a given speed is reached the ship will continue its motion due to the inertia.
January 24, 2008maddie (virginia/usa)how/why does a solid sublimate?At normal pressures most sustances are able to exist in three different states at different temperatures. For example, when increasing temperature a solid will transition to a liquid state and, if we continue increasing temperature, the liquid will transition to gaseous state. However, for some elements or substances at some pressures the material may pass directly from solid to the gaseous state. This happens when the exterior pressure exerted on the substance is too low to stop the molecules from escaping from the solid state.
January 22, 2008Bob (ON)I have a class of students who are in applied so they have so many questions and they keep bothering me with this 4th dimension universe and if its possible. How can I explain it in terms they'll and me for that matter will understand?Since the conception of the Theory of Relativity, the spacetime continuum has been considered one entity, and it is accepted to consist of 4 dimensions.
January 21, 2008Bob (South Africa)If a silver object and white oject reflect all wavelengths,shouldn't they appear identical? Why does a white sheet not appear silver or a mirror not appear white?Silver and white objects reflex different wavelenghts. Granted, they are only slightly different, but this difference makes the objects of different colors.
January 16, 2008ian (ON)Is the mass of electrons different for each element? So is the mass of a hydrogen electron different from the mass of say an iodine electron?No, the electron is the same particle for every element. Its mass is always 9.10938188 × 10-31 kilograms.
January 16, 2008Ian (ON)I understand that uranium has a decay and is unstable so it will break down until it is a stable element. Whenever it changes from one element to another I can't help but wonder if there is some matter that just vanishes because you can't just break down an element perfectly. I know that the products are a smaller element, excess neutrons, and energy. Is the decay of matter an exception to the law that matter can't be created or destroyed?This is the same issue as your last question. Matter is a form of energy, and radioactive elements are emitting precisely that, energy.
January 16, 2008Ian (ON)How can the universe expand and still maintain the same amount of energy inside it. Shouldn't the law of conservation of energy be saying that the amount of energy stays in a fixed ratio that is always the same? (amount of energy:amount of space it is enclosed in)The total amount of energy of a closed system will remain constant. Of course, there are transformations from one form to other, but the net result (keep in mind that mass is a concentrated form of energy!) is always the same.
January 16, 2008Philosopher (ON)I understand that energy drives forces. Where is the energy coming from to give the "opposite reaction force" from newton's third law? The energy used to drive the force applied must not be able to drive the reaction force as well. If so then how much energy is used for the applied force and how much for the reaction force?The issue is a little more complex, and involves the relative velocities, positions, etc. of the interacting objects. The net linear momentum of the system (both objects) will remain constant through the interaction, and the kinetic energy of the objects will change correspondingly. This forum could help you to understand better the issue.
January 16, 2008Ian (ON)Why is there gravity and why can't there be antigravity like a force that pulls objects apart?Gravity is a function of the interacting masses and the distance between them. So far, besides especulations, there is no any proof of the existence of anti-gravity. However, new ideas are being discussed among scientists. This article offers an interesting theory.
January 15, 2008angelica (philippines)what are the weather elements and give example instruments that matches the element?The weather elements, are those of wind (can be measured with an anemometer), temperature (thermometer), pressure (barometer), humidity (hygrometer), clouds (observation), and precipitation (pluviometer).
January 7, 2008Katherine (Canada Ontario)what is a lightyear?1 lightyear = 9.4605284 × 1015 meters, which is the same as 9 460 528 400 000 000 meters, or 9 460 528 400 000 km, or 5 878 499 810 000 miles.
January 7, 2008Peter If a force is applied to the body (to accelerate it in some direction), such as from the gravity of another near by body, how would it alter the first body's orbit?The answer to your question escapes the reaches of this secton, but you can find information about this topic at the web page Applied Orbit Perturbation and Maintenance from the Aerospace Corporation.
January 3, 2008sabrina (flordia)what are some characteristics of solids?Solids hold their own shape. The molecules and atoms of solids don't move around, they only vibrate in place.
January 2, 2008joe (Nevada, USA)are all the rays of the sun reflected from a mirror?No, even in the most perfect mirror there is still some energy transferred form the Sun rays to the mirror.
December 27, 2007julie (arizona)what is circular motionIt is a motion that follows a circular path around a center of rotation.
December 26, 2007Kevin (Belgium)Why do objects (and people) experience g-force when an acceleration occurs or when you're on the inside of a wheel like in 2001: A Space Odyssey ?This effect is describe by Newton's First Law, The Law of Inertia: "If the net force acting on a particle is zero, then it is possible to select a set of reference frames, called inertial reference frames, observed from which the particle moves without any change in velocity." In a simplified form, this law can be expressed as "An object will stay at rest or continue at a constant velocity unless acted upon by an external unbalanced force". In other words, to change the motion of a system (accelerating it, for example), a net force different from zerdo has to be applied.
December 20, 2007glenn (texas)what is boyle's lawBoyle studied the relationship between the pressure and the volume of a confined gas held at a constant temperature, and found that the product of the pressure and volume under these conditions is almost constant: pressure * volumen = constant
December 18, 2007rix (philippines)what is newton's synthesis?Newton's Synthesis (better described in his book Principia) lays the foundations of modern physics, replacing older, empirical descriptions with quantifiable, physical explanations of the natural phenomena, and unifying all motions into three simple laws.
December 12, 2007eilon (asia)what are some examples of fundamental forces?The Fundamental Forces are: Strong (the forces that hold a nucleus together), Electromagnetic (forces between charges and the magnetic force), Weak (changes one flavor of quark into another), and Gravitation (an attractive force acting along the line joining the centers of mass of the two masses).
November 5, 2007phebe (rhoade island)what makes the sky blueThe sky appears blue because the atoms of the atmosphere separate the white light from the Sun into its many colors, and scatter them throughout the atmosphere. The blue light scatters better than the rest and makes the sky appear blue to us. For more information visit oour web page Why is the sky blue?.
October 16, 2007Ronnel (Philippines)What are the law of thermodynamic?Due to the restricted space here, the answer will be limited to the simplest form of these laws. These laws are very complx, with a very high level mathematical basis. It would be good to explore more about this topic. First Law of Thermodynamics: Energy can be changed from one form to another, but it cannot be created or destroyed. The Second Law of Thermodynamics states that "in all energy exchanges, if no energy enters or leaves the system, the potential energy of the state will always be less than that of the initial state." (This is also commonly known as entropy.)
October 16, 2007Winnie Just wondering....How does an alternating current (AC) vary the direction of its electrical current?In alternating current (AC) circuits the voltage oscillates in a sine wave pattern. Because the current is related to voltage (by the Ohm Law), the current will also oscilates, changing its "direction" as a result of the changing voltage.
October 16, 2007Wayne (Ontario Canada)When using a vacuum chamber to boil water, Can the boil be maintained by adding more water without disturbing the vacuum pressure?The state of a gas is determine for the ideal gas law, the relation between volume, pressure and temperature, and it includes the amount of substance. Changing any of these parameters will change the state of the system. To answer your would require a clear definition of the state of the system. This page offers more information on this topic.
August 21, 2007Aheli (India)What is the exact meaning of Energy? Please try to explain me in full details rather than giving just the Formula of it.In Physics, the most basic definition of energy is the capacity of a physical system to do work.
August 21, 2007CATHI (INDIA)WHAT IS QUANTA?Quanta is the plural of quantum. In physics it refers to an indivisible entity of energy.
July 26, 2007brijesh (west bengal/india)if we ignite a cigarette lighter or a match box inside space station,why does fire take a round shape?in other words my question is when fire is made out of any mean(match box, lighter etc)in an oxygenated chamber in space, why does fire takes a round shape?All systems tend to a state with the minimum energy. If there is no rotation and no displacement (angular momentum and kinetic energy are zero), the perfect shape, with the minimum gravitational potential energy U, is a round ball.
July 25, 2007Bertus van (South Africa)I would like to know, in theory, wat would happen if you could drill a hole through the earth and drop a small object right down the middle of the hole?If a small rock, for example, is dropped at the equator, and assuming that Earth density is spherically symmetric, then the mass acting gravitationally on the object is proportional to the cube of its distance from the center of the planet. So, as the object travels toward Earth's center, the gravity acting on it would decrease, until there's no net gravitational force at the center itself. As a result, a dropped rock would follow an elliptical path in Earth's equatorial plane, with Earth's center at the ellipse's center. More information can be found in this interesting article.
July 25, 2007Elizabeth (Ontario Canada)Satellites are placed in orbits with different altitudes for different purposes.The speed of travel of the satellites is also different which of these different kinds of satellites travel the fastest? how does their speed compare to the speed of the planets?This is an interesting problem to solve (which involves the definitions of centripetal and gravitational forces), but the straight answer is: The closer the satellite is to the earth the quicker the satellite has to move.
July 23, 2007Edward (Louisiana)Is time real? Theoretically isn't it just our earth orbiting around our sun.Yes, time is real, very real. It is not only a conventional way to measure our life (considering a day one full revolution arount the planet axis, and a hour equal to 1 day/24), but is a dimension on which everyting exist and change.
July 23, 2007Veena (india)what is four dimention?The three "classic" dimensions are x,y,z, related to depth, width, and height. The fourth dimension is often identified with time, and as such was used by Einstein to explain space-time in his theories of special and general relativity.
July 21, 2007deepak (vizag.india)Ultraviolet radiation oscillates at rates between about 800 terahertz (THz or 1012 hertz) and 30,000 THz.????
Ultraviolet Radiation
UV frequencies cover from 7.5 x 1014 Hz to 3 x 1016 Hz or from 750 THz to 30 000 THz.
July 21, 2007mariecel (philippines)will the density of a mercury bar increase with an increase in weight?Density is defined as the ratio between mass and volume. Weight, on the other hand, is the gravitational attraction of our planet (or any other planetary mass) over a given body. When weight is increased (and if there is no other changes, like n temperature), both mass and volume are proportionally increased, so density stays constant.
July 20, 2007Victor (Australia)Does the addition of heat to a substance automatically change its mass?NO. The change of the net mass of a given body could be product of the addition of heat, but there are many other effects that could occur before, including changing the state of matter.
July 18, 2007GABY (CA)what are two types of radiation that we cannot see & what do they cause?There are many types of radiation we can't see. Our webpage The Electromagnetic Spectrum should answer your question.
July 17, 2007Kiruba (INDIA)which of the 4 meteorites will cause maximum damage when impacting on the earth?
a)1000gm meteorite moving at the speed of 20km\sec
b)100gm meteorite moving at the speed of 100km\sec
c)100000gm meteorite moving at the speed of 1km\sec
d)10000gm meteorite moving at the speed of 5km\sec
The linear momentum of a body is calculated as: p = m*v The greatest damage would be inflicted by the object with most momentum. From your data this object is c.
July 17, 2007Jeff (Georgia/USA)If two like magnetic poles were melted or fused together, would the two poles be demagnetized or could they somehow form a bond that could create a magnetic field that would be stronger than the original field before the two magnets were fused or melted together? If a stronger field could be formed, could its energy be harnessed since magnetic fields and electricity are so closed related?The only problem with this idea is that magnetic poles exist only in pairs. For every negative pole there is a positive one, and vice versa.
July 13, 2007rachita (india)why while revolving, planets do not fall towards the sun?Because there are other forces than gravity acting over the planets. All rotational motion involved two main forces, the centripetal (from the Latin words centrum "center" and petere "tend towards") force, and the centrifugal ("from Latin centrum "center" and fugere "to flee") ") force. In planetary systems, the centrifugal force is gravity, and it is balanced out by the centrifugal force, so the planets and other bodies will keep rotating around the Sun.
July 11, 2007Ian (on)What is a nucleosynthesis reaction?Nucleosynthesis is the process of creating new atomic nuclei from preexisting nucleons (protons and neutrons).
July 11, 2007umar (pakistan)why some heat is lost in space while covering distance whereas there is no heat absorbig matter in space(whan there is no planet or other atter body in the path)?Temperature is a manifestation of the kinetic energy of the particles. Interactions with other particles, planetary magnetic fields, etc, will change the average value of the energy of the particles.
July 10, 2007SHANNON (CA)What is a mineral?There are many definitions of minerals, one of them is: Minerals are natural compounds formed through geological processes.
July 10, 2007Lyndae (Bahamas)Why is particules in gasses so spaciousDue to the high kinetic energy they have, the particles move more freely. This characteristic keep the particles in gas more separeted from each other.
July 9, 2007jeffrey (Canada)What is the Ratio of the Speed of light in Vacuum divided by the Speed of Light in airThe speed of light is lower in transparent media (i.e., air, water, glass, etc). The ratio by which it is slowed is called the refractive index of the medium and is always greater than one. This was discovered by Jean Foucault in 1850.
July 6, 2007Mike (PA)why do scuba divers get the bends when they come up to fast and there ears hear when they go down to fastMany situations can produce the Decompression Sickness a.k.a. bends. for example, the failing of the cabin pressurization system of an aircraft also provoke the DS. Situations like these cause inert gases, generally nitrogen, which are normally dissolved in body fluids and tissues, to come out of physical solution and form gas bubbles.
July 6, 2007Ezma (Australia)What is Energy?In Physics, energy is the capacity of a physical system to do work. Energy is expressed in joules or ergs.
July 6, 2007Md Ehshan (Nepal)What will be the effect of the acceleration due to gravity while jumping with a parachute?While free-falling you will still get an acceleration of 9.8 m/s2. After the deployment of the parachute, an analysis of the gravitational force and the friction forces due to the parachute is required. This page have a good description of the problem.
July 3, 2007samantha (wyoming )why does water appear on the outside of a ice water on a hot sunny dayBecause the moisture contained in the air condensate with the low temperature of the wall of the glass.
July 2, 2007HULA (New Jersey)How much radiation can you be exposed to should a nuclear power plant have a meltdown?The limit of radiation for workers varies from country to country. for example, 50 mSv is the yearly federal limit for radiation workers in the United States. In the UK the yearly limit for a classified radiation worker is 20 mSv. In Canada, the single-year maximum is 50 mSv, but the maximum 5-year dose is only 100 mSv. (Sv = Sieverts)
July 2, 2007sarah (NSW australia)what are the physical changes acssociated with tha making of toffee? use the Particle and Kinetic theory to explain the change of states.The use of the Kinetic Theory does not change when explaining the change of states. With the increment of temperature, the amount of kinetic energy of atoms and molecules increases, and the substance passes from solid to liquid, and then, if energy is still being provided to the system, to gas.
June 28, 2007alyson (michigan)What is the SI unit of temperature?The thermodynamic temperature is one of the SI basis unit. It is expressed in kelvin (K). However, the Celsius temperature, expressed in degree Celsius (°C) is a SI derived quantity. more information about the I units at NIST.
May 22, 2007Ian (Canada)I learned in science class, the laws of thermodynamics state that energy can't be destroyed or created, it can only be transfered. When matter cools or heats up why do the particles gain or lose energy?You have the basic concept right. When the temperature of the system is higher, the kinetic energy of the particles is higher. In other words, temperature is directly related to the kinetic energy of the molecules (molecules also have potential energy). If the temperature is expressed in Kelvins, then it is proportional to the average kinetic energies of the molecules. The expression that relates both is: KE = 3/2 kT where KE is the average molecular kinetic energy and k is the Boltzmann's constant (= 1.380×10−23 joule/kelvin.
May 11, 2007Mia ( PA)If one of the characteristics of a mineral is that they are inorganic, and diamonds are made from coal ( an organic material) why are diamonds considered to be minerals?It depends of the definiton of minerals (some are very narrow). If we think of a mineral as solid created by natural forces and is a chemically pure substance (it only has one kind of chemical compound), then diamonds are a mineral.
May 11, 2007Steve (Michigan, United States)How do magnets work? By this I mean, what is different about a magnet, permanent or induced, that gives it the forces we observe? It has to be something at the atomic level I would imagine, could you explain this please? Thanks.The atoms in ferromagnetic materials naturally tend to get together in small groups known as domains. In each domain the atoms tend to point in the same direction, making then to behave like small bar magnets. This define the magnetic characteristics of magnets. For a more detail information, visit Magnets.
May 10, 2007Jerky (Indonesia)What is an AuroraAurora is an atmospheric phenomenon consisting of bands of light caused by charged solar particles following the earth's magnetic lines of force.
May 10, 2007seth (Illnois united states)who discovered that there were different wavelengths of light?Thomas Young's experiments, in the 18th century, took him to propose the wave theory, and that light could be polarized. He also proposed that different colors were caused by different wavelengths of light.
May 10, 2007Ian (Canada)If it were possible for matter to go below 0 degrees kelvin what would probably happen to the matter? Why?Zero Kelvins, or absolute zero, which is theoretically unreachable, means no thermal motion, but it wouldn't apply to other types of energy, like gravity.
May 10, 2007Audrina (Chicago )what are the main types of electromagneticElectromagnetic radiation is classified according to the frequency of the wave. In order of increasing frequency they are: radio waves microwaves terahertz radiation infrared radiation visible light ultraviolet radiation X-rays gamma rays
May 7, 2007tiffany (Canada)How do scientists classify matter and what are some Homogeneous and Heterogeneous mixtures?One classification scheme for matter follows this: Matter can be classified as Mixtures or Pure Substances. Mixtures are Homogeneous or Heterogeneous. Pure Substances are Compounds or Elements. Mixture are two or more substances, combined in varying proportions - each retaining its own specific properties. The components of a mixture can be separated by physical means, i.e. without the making and breaking of chemical bonds. Examples: Air, table salt thoroughly dissolved in water, milk, wood, and concrete. In Heterogeneous Mixtures the properties and composition are not uniform throughout the sample. Examples: Milk, wood, and concrete. In Homogeneous Mixtures the properties and composition are uniform throughout the sample. Examples: Air and table salt thoroughly dissolved in water.
April 13, 2007ABHAY (INDIA)WHY CANT WE CATCH THE SPEED OF LIGHTActually, the limit established by the modern physics is the speed of light in a vacuum, 299 792 458 m/s (meters per second). At the present time most scientists believe that the correct answer should be "no". However, it has to be emphasized that there is no definite proof for this claim. A "light" treatise on the subject can be found here.
March 31, 2007whitney (wv/united states)List six kinds of places on earth where water is found.Name the state of the water in each place.1. Oceans and seas: liquid. 2. Lakes: liquid. 3. Rivers and creeks: liquid. 4. Polar caps: solid. 5. Icebergs: solid. 6. Over a boiling pot of water: water vapor.
March 30, 2007Loraine (Ohio)When we are studying the phases of matter, my students often have questions about the fourth state of matter: plasma. They often want to know if this plasma is the same as "plasma" televisions. Is it the same?? How can I best explain plasma to my sixth graders? Plasma is known as the fourth state of matter. Under normal conditions the electrons (which have a negative charge) are attracted to the nucleus (positive charge), but sometimes there are conditions under which the electrons escape the attraction of the nucleus. One possible cause is extremely high temperatures. The basic idea of a plasma display is to illuminate tiny colored fluorescent lights (red, green and blue) to form an image. The central element in a fluorescent light is plasma, a gas made up of free-flowing ions and electrons. From these two (very) basic descriptions, plasma displays indeed use plasma.
March 21, 2007Alex (Philippines)Can you explain to me combustion in a simple way?A simple definition of combustion is: a complex sequence of exothermic chemical reactions between a fuel and an oxidant accompanied by the production of heat or both heat and light in the form of either a glow or flames. In the large majority of the real world uses of combustion, the oxygen (O2) oxidant is obtained from the ambient air and the resultant flue gas from the combustion will contain nitrogen. (from Wiki/Combustion).
March 21, 2007shaelyn (NSW, Sydney)Can you explain the process of gravity?Gravity is a common force first studied by Newton. He expressed his Law of Universal Gravitation as "Each particle of matter attracts every other particle with a force directly proportional to the product of their masses and inversely proportional to the square of the distance between them." The mathematical formula for the force of gravity is: Fg = (G * m1 * m2) / (r2) where G is the gravitational constant, m1 and m2 are the masses of the two objects, and r is the distance between the two masses. Because G is a very small value (6.67 x 10-11 N m2 kg-2 = 0.000 000 000 066 7 N m2 kg-2 ), it is hard to observe the gravitational atraction between two small objects.
February 28, 2007Mikila (CA, USA)why does the liquid in a thermometer move when the temperature changesThe change of the fluid in the thermometer responds to a common characteristic of all substances; everything expands with an increment in temperature.
February 20, 2007ANA (calfiana)What do u know about LILagrangian points are points where the gravitational forces acting between two objects are balanced. The L1 point lies around 1.5 million kilometers inside the Earth’s orbit, in a point between the Sun and the Earth. A spacecraft located at this point will ‘hover’.
February 12, 2007kobel (oregon)what is the doppler effect?A basic definition of the Doppler effect is the change in frequency of a wave perceived by an observer moving relative to the source of the waves.
February 12, 2007Elizabeth (Michigan)What really is a crystal and why? (in kid words)In very few words, a crystal is a solid in which the atoms are packed in a pattern.
February 12, 2007lanez (california)what is the name of the experiment that was done to prove that the earth rotates on an axis?The best known experiment that proves the rotation of the Earths on its axis is the Foucault's pendulum. A very detailed explanation of this experiment can be seen at
December 20, 2006TAYLOR (LA/U.S)WHAT SHOULD I PUT IN A PAPER TN THE STATES OF MATTER?The four states of matter are solid, liquid, gas, and plasma. If we use water as an example, the first three states would be as follows: ice (solid), water (liquid), steam (gaseous). The plasma state for water would be made up of hydrogen nuclei and electrons. Stars are made of plasma, so plasma is the most abundant form of matter in the universe.
December 13, 2006Mikayla (Idaho)I am trying to find infromation on convection but every website I go to just is way over my level answers, can you help?Convection is the internal movement of currents within fluids (liquids and gases). The most common cause is a variation in density due to transfer of heat. For more information: href="http://en.wikipedia.org/wiki/Convection"
December 9, 2006Jessica (uk)why does light from far away galaxies take longer to reach us than light from the sun?Because the speed of light is a finite number, about 300 000 km/sec (exactly 299 792 458 m/s).
December 9, 2006Paul (texas)For science fair project: How does infrared radiation compare to visible light?Infrared (IR) radiation is electromagnetic radiation of a wavelength longer than that of visible light, but shorter than that of radio waves. For more information, please visit http://en.wikipedia.org/wiki/Infrared
December 9, 2006Melyna (Michigan)Who was Archimedes and how did he use density to slove a problem?Archimedes (c. 287 BC – 212 BC) was a Hellenistic mathematician, physicist, engineer, astronomer, and philosopher, born on the seaport colony of Syracuse, Magna Graecia, what is now Sicily. Many consider him one of the greatest, if not the greatest, mathematicians in antiquity. Legend has it that Archimedes discovered his principle of buoyancy, which states that the buoyancy force is equal to the weight of the liquid displaced, while taking a bath, upon which he is supposed to have run naked through the streets of Syracuse shouting "Eureka!" (I have found it!). He was tasked with determining if a craftsman had defrauded the King of Syracuse by replacing some of the gold in the King’s crown with silver. When taking a bath he realized that the amount of water spilled was equal in volume to the space that his body occupied, and used this to solve the task. The same amount of silver and gold, because their different densities, occupy different volumes, and displaced different amounts of water.
December 6, 2006Shravya (INDIA)what is light?Light is electromagnetic radiation with a wavelength that is visible to the eye (visible light) or in a scientific context, electromagnetic radiation of any wavelength. For more information, visit: http://en.wikipedia.org/wiki/Light
December 6, 2006Jessica (U.S)Will magnetism be lost or gained in different tempertures?Absolutely, a ferromagnetic material loses its characteristic ferromagnetic ability when its Curie temperature point is reached. For this type of magnets (iron-based) there are not important changes at very cold temperatures. Another type of magnets, electromagnets, is improved by low temperature. Low temperatures make the resistance of the copper wire lower, and a stronger field can be obtained by applying higher currents, without overheating the wire.
December 1, 2006deontae (kansas city missouri)what are the states of matterThe four states of matter are solid, liquid, gas, and plasma. If you think of water as an example material, the first three states would be as follows: ice (solid), water (liquid), steam (gaseous). The plasma state for water would be made up of hydrogen nuclei and electrons. Stars are made of plasma, so plasma is the most abundant form of matter in the universe.
November 30, 2006DEDEEPYASINH (INDIA)WHAT DOES PLASMA CONTAIN AND WHERE IS IT FOUND?Plasma is known as the fourth state of matter. Under normal conditions the electrons (which have a negative charge) are attracted to the nucleus (positive charge), but sometimes there are conditions under which the electrons escape the attraction of the nucleus. One possible cause is extremely high temperatures. Most of the matter in the universe is found in the plasma state. That is because stars contain so much of the matter in the universe (stars are so hot that their matter can only exist in the plasma state). For more information visit our page The Plasma State
September 24, 2004Tammi (Ohio)What is a unit of electromotive force?Electromotive force or emf is the measure of the difference in electric potential, or voltage, between the terminals of a source of electricity. It is measured in volts.
July 31, 2001Anthony (New York, USA)What would happen if you were to hit a ball while in outer space with a baseball bat?Assuming you could actually hit the ball (a spacesuit might make swinging a bat pretty hard), the ball would keep flying until it hit something else or passed near enough to a celestial body (something with a lot of mass) to be attracted by gravity and fall toward that body.

Since the ball would basically never stop until it hit something, it would mean a game of baseball would use up a lot of balls if you didn't have good outfielders!

March 27, 2000---How many molecules are in a single drop of water?My best estimate is that there are 10^21 molecules of water in a single drop of water. That's a thousand times a billion times a billion molecules of water in one single drop!
March 22, 2000Doug (Florida, USA)What percentage of the sun is helium?25% of the Sun's mass is helium. 73.4% of the Sun's mass is hydrogen. The next most abundant atoms are carbon, nitrogen, oxygen, neon, and magnesium. They make up about 1% of the Sun by mass.
March 9, 2000Michael (Ohio, USA)Can you explain the process by which an electrical current is converted into heat for a toaster ovenWhen you pass an electric current through a material that doesn't conduct electricity very well, you generate a lot of heat (the material resists the flow of electrons). A toaster has filaments of resisting material, and to toast bread all you have t o do is pass a current through these resistors and put your bread close to them for a few minutes.
March 9, 2000Lakreshia (Michigan, USA)How do preservatives keep bacteria from growing?Most preservatives are antibiotics (in a way). They're chemicals that poison the bacteria around them, so the food never spoils. Unfortunately, they're also not the greatest things for us to eat either, which is why a lot of people try to eat "natu ral" or "organic" foods.
March 9, 2000Raikeisha (Michigan, USA)Will vitamin c help keep a banana from turning brown? Why?Vitamin C should help keep bananas from looking brown, though it depends on which Vit. C you're trying this with. A lot of Vit. C is sold in a form that's easier for people to digest (sometimes called esterified Vitamin C), and this form won't work ( or at least not nearly as well as the natural kind). A better thing to use for this is citrus juice, because it's very acidic. The process that turns fruit (like bananas or apples) brown is called oxidation, and things that are acidic (like citrus juice) or things called "reducing agents" (Vitamin C is one of these) prevent oxidation from happening.
March 9, 2000Carl (Montana, USA)Why does hot water freeze faster than cold?Newton's law of cooling says that a body of water changes temperature at a rate proportional to the difference between it and its surroundings. Put another way, hot water thrown on a cold surface changes temperature faster than cold water dumped on t he same surface, but the cold water will actually become ice (freeze!) first.
March 8, 2000Coby (Tennessee, USA)I need to why mineral rock salt, rubbing acohol, sand Cat litter, and sodium cloride melts ice.Rock salt, rubbing alcohol, and sodium chloride all disrupt the crystalline structure of the ice, weakening it and promoting melting. Sand and cat litter don't do much to melt ice-they're mostly used in the winter to give traction.
March 8, 2000Chris (Colorado, USA)Why does water taste so sweet after you eat an artichoke?I've never done this, but I think the answer is because your tongue sometimes senses how much sugar something has relative to the last thing you tasted. If an artichoke is sour or bitter, then the next thing you taste (whatever it may be) will be swe et, because there wasn't much sugar in the artichoke. This is the same reason orange juice can taste pretty sweet early in the morning, but after a bowl of Fruity Pebbles, it tastes pretty sour! Your tongue is used to all the sugar in the cereal, and that makes the OJ taste low in sugar.
March 2, 2000Curtis (California, USA)How do light bulbs work?In a common incandescent light bulb, an electric current flows through a double-spiral coil of very thin tungsten wire. As the electric charges in the current flow through this tungsten filament, they collide periodically with the tungsten atoms and transfer energy to those tungsten atoms, heating the tungsten filament to about 2500° C.

Very hot objects emit some of their thermal radiation as visible light. A 2500° C object emits about 12% of its heat as visible light and this is the light that you see coming from the bulb. Most of the remaining heat emerges from the bulb as invisible infrared light or "heat" light. The glass enclosure shields the filament from oxygen because tungsten burns in air.

January 11, 2000Natalie (Canada)If an astronaut had a thermometer in space, would it work? if so, what would the temperature be?Well, if it went low enough it would work! Most normal thermometers would freeze. The temperature in outer space is 2.7 Kelvin, or -270.5 degrees Celcius.
November 17, 1999Katie (Washington, USA)Why after you take a bath and pull the plug in the northern hemisphere the water forms a little water cyclone and the water flows clockwise, and in the southern hemisphere it flows counter clockwise?Try looking here!
November 1, 1999Joe (Michigan, USA)Imagine a very large box, sealed on all sides, with a bird flying around inside of it and the box sitting on a very large scale measuring its weight. If the bird lands will the scale register a higher weight, the same weight, or less weight?The scale will register a higher weight. Do you know why?

When the bird is flying around, it is not part of the box's mass. The bird is supporting its own weight, so the scale does not register the bird's mass.

However, when the bird lands on the box, it is no longer supporting its own weight. The box is now holding up the bird, so the bird's mass is added to the mass of the box. The registered weight will then increase.

October 23, 1999Nell (Oman)How does a yo yo work?A yoyo stores energy. As it is thrown to the ground, the string unwinds. A quick jerk on the string while the yoyo is still spinning allows the string to bunch up and cause extra friction between the string and the axle, which causes the yoyo to win d up.
October 18, 1999Lauren (Texas, USA)Why is diamond a mineral, since it is formed from coal, which is a rock?Many people know what a rock is, but they don't know what they are made of. Rocks are actually made of minerals! A rock is made of tightly packed minerals. Rock may be made of a single mineral or several minerals mixed together.
Minerals are made of chemical elements. Both diamond and coal are made of the element carbon. When plants and animals die, they produce carbon in the ground. Over time, the carbon becomes coal.
If the temperature increases enough, the coal can become graphite, which is used in pencils. And if it gets even hotter, the graphite will become diamond!
Even though there is a lot of carbon in the earth, don't try to dig up diamonds. You'll have to dig at least 100 kilometers down before it is hot enough to make them!
September 21, 1999Melecio (California, USA)I was told that you can approximate the distance of near stars by using some kind of triangular formula, what is the formula?There is a very simple formula you can use to find the distance to stars. The distance is equal to one divided by the parallax, or d=1/p, where p is the parallax.

This equation is based on geometry. If you look at an object close to you as you walk by, it appears to move! For example, look at a tree close by while looking at the scenery behind it. As you move, the tree seems to move relative to the background.

This is also used to measure distances to stars. As the Earth moves around the Sun, the star you are measuring appears to move relative to the stars behind it. To find the distance, first look up the parallax in a book. The parallax is the angle between the Sun and Earth, from the star's point of view.

Divide 1 by the parallax, and you will have the distance in parsecs! (One parsec is 3.26 light years, or 100,000,000,000,000 kilometers!)

August 9, 1999Phil (Australia) How high can a balloon go?How high a balloon can fly depends on two important concepts, pressure and density. When you are holding onto a balloon, it wants to fly up because the gas inside it is less dense than the air around it. To better understand density, poor some oil and water into a glass. The water is less dense, so it floats on top of the oil!

As long as the gas inside the balloon is less dense, it will fly higher and higher. Soon it will run into a problem! Lower to the ground, the pressure is very high. Think of pressure as the weight of all the air on the balloon. As the balloon floats higher, the pressure outside gets lower, because less air is above the balloon.

Eventually, the pressure outside is less than the pressure inside. This makes the balloon expand. Expanding makes the air less dense, so the balloon keeps going higher! Eventually, the balloon can't expand anymore, and it pops!

May 24, 1999Jenni (Minnesota, USA)Why do shiny pans get hotter than colored or dark pans when they are put in the oven?Theoretically, dark pans bake hotter than shiny pans do. This is because the shiny pan reflects the heat, while the dark pan absorbs more heat, making a hotter baking surface.
May 20, 1999Julia (Cumbria, United Kingdom)I know that energy converts into different forms, but when fuel is burned and the energy is converted into heat, the heat then rises... and then what? Surely as the heat cools the energy is lost, if not where does it go and into what form of energy?This is the right idea. However, instead of thinking of 'heat cooling', think of a gas first being heated and then cooled. It is correct to say that energy is converted into heat. When a gas molecule cools, it also loses energy. That energy is released into the surrounding air and is absorbed. This in turn raises the temperature of the surrounding air!
April 30, 1999Bob (British Columbia, Canada)How many colors are thought to be in the spectrum?There are said to be seven colors in the sunlight spectrum: red, orange, yellow, green, blue, indigo, and violet.
April 12, 1999Jake (Wisconsin, USA)How fast does rain fall?The average raindrop falls at a speed of seven miles per hour.
April 8, 1999Edward (Florida, USA)How does salt water affect bouyancy?Objects float because the liquid pushes them up with a force equal to the weight of the liquid displaced by the object. Salt water weighs more per unit volume because of the minerals dissolved in it. This means it is denser, and holds the object up with a greater force than fresh water does. So, salt water makes things more bouyant.
April 8, 1999Sam (Australia)Does a person inside a plane travelling at the speed of sound hear the sonic boom?No. The sonic boom forms a cone over the nose of the plane, which travels with the plane--sort of pushed along by it. Only people on the ground hear the boom when it passes over them.
February 11, 1999Btb Why is it quiet after a snowfall?The snow covers everything and absorbs and muffles the sound. The effect is similar to walking through an empty room with no carpeting. Every noise is loud and it echos. Then when carpeting and curtains are added, the sound level returns to what we are used to.
February 6, 1999Paul Does cold fusion leave any traces of raditaion and how close are we to reaching it?Cold fusion does not produce radiation. This is one of the unsolved mysteries about cold fusion. Cold fusion is considered by mainstream scientists to be highly theoretical, and is a controversial subject. However, there are a few laboratories and wealthy scientists still researching it, so perhaps in the future a definite conclusion can be reached on the matter.
January 6, 1999--Would it be possible to create a short beam of pure energy about a meter or so long? Kind of like those lightsabers on the Star Wars movies.It is possible to make a fairly stable plasma cord which will burn for a while. However, it can only be created in an extremely high vacuum. Also, large complicated magnet systems are needed to make them.
December 22, 1998Jamey What are the odds that a person's eyes will be closed in a photograph? Assume the subject is not aware of being photographed, so won't be holding the eyes open on purpose. I'm having trouble finding out how many times a normal person blinks per minute.People blink on average every 5 seconds and each blink lasts about 1/3 of a second. So, a person's eyes will be closed about four seconds out of every minute. That means there's about 7% chance that their eyes will be closed in the photograph!
November 21, 1998Dana (North Carolina, USA)Is toothpaste a liquid or a solid??Toothpaste is a non-Newtonian fluid. It has a yield stress, which means that below this stress it acts like a solid, and above this stress it flows like a liquid.
November 19, 1998Rodney (California, USA)If two people of the same exact strength arm wrestle, one with forearm measured from elbow to finger tip as 18", and the other person a measure of elbow to fingertip of 15", who has the advantage? Keep in mind that each has the same muscular strength,-- that is each can bench press the same amount of weight.That depends on how theoretical you want to be. In a text book manner, the important idea here is leverage. For example, if you had to change a tire on your car, you would prefer a longer wrench over a short one because it would give you more leverage around the pivot point, the lug nut. For the same reason, the person with the longer arm would have an advantage as their arm pivots around the elbow.
However, arm wrestling is an organized sport, with rules and techniques, and the arm itself is a complicated mechanism. As I don't know the exact rules of arm wrestling, it is hard to give a definite answer.
November 2, 1998Thomas (New Jersey, USA)How do you find the 'sweet spot' on a baseball bat?There are three different "sweet spots" on a bat. When the bat hits the ball, if the impact is at the end or on the handle, the bat will vibrate. At a spot about 15 centimeters from the barrel end of a typical bat, the wavelike motion is zero (hitti ng the ball here would be like trying to rotate a seesaw by pushing on its axis). This is the "node" sweet spot. There is a second "rotational" sweet spot where the bat will pivot around the hands (not disturbing them) as the ball strikes. At the third sweet spot, the "center of percussion", your hand won't feel any force pushing against it. You can find it fairly easily.
October 30, 1998Somerville HS. Calc Class(New Jersey, USA)Do you know the application for the fourth derivative (jounce?). Also do you have any information on Jerk, the application of the 3rd derivative. I don't think there is an application for the 5th 6th 7th etc. but if i'm wrong, please tell me about those too! The rate of change of acceleration - or the third derivative of position with respect to time - is known as jerk. Jerk is important when looking at the destructive effect of motion on an object. The movement of delicate objects has to be within limit s of jerk as well as acceleration to prevent damage. Train engineers, for example, keep the jerk less than 2 metres/sec^3 to avoid passenger discomfort.

In the case of the Hubble space telescope, the engineers are said to have gone as far as setting limits on the magnitude of the fourth derivative, often called jounce. There is no official term for the 4th derivative.

One suggestion has been to use snap, crackle, and pop for the 4th, 5th and 6th derivatives respectively. Dork has also been suggested for the sixth derivative.

October 28, 1998Carolina (Gibraltar)How do you find the mass of a planet?The mass of a planet is found by determining the orbital period of one of its satellites, and the distance of the satellite from the planet. The period and distance are related to the mass by Kepler's third law, which says that mass = 4*Pi^2*distance^ 3/(G*period^2), where G is the gravitational constant 6.67x10^-11 m^3/(kg*s^2) and Pi is 3.142.

Some planets such as Mercury and Venus don't have satellites, so NASA sent manmade ones and measured how the planet perturbed the trajectory. The idea is the same. You can also approximate the mass by knowing the size of the planet and assuming a typical density for its composition.

September 10, 1998Michael (North Carolina, USA)By definition what is an electric charge?Charge is an intrinsic characteristic of fundamental particles. This means it is a characteristic which accompanies those particles wherever they exist. Charge is one of the four dimensions. Mass, length, time, and charge can be combined to measure all other properties, such as volume(length^3), density(mass/length^3), velocity(length/time), and current(charge/time), as well as many others.
August 20, 1998Derek (Canada)What is space made of? If there is no air in space as I have heard someone say, then how can spaceships' thrusters control where the spaceship goes?Space is pretty much just that...empty space! There are a few particles floating around, but not even as much as would be contained in a gaseous nebula. The movement of rockets has to do with Newton's third law, which says that for every action, there is an equal and opposite reaction. Rockets work by releasing matter backwards into space. This provides thrust, which moves the rocket forward. It's kind of like blowing up a balloon, then letting it go to fly around the room. That's thrust!
May 16, 1998Deana (Missouri, USA) What substance(s) can neither be melted by extreme heat or frozen beyond use in the coldest temperatures, and is also lightweight? Can this substance withstand without being crushed by extreme pressure? NASA is still experimenting with a truly remarkable material called aerogel. It is the closest material I have heard of that fits your description. Aerogel is the world's lightest solid made principally from silica. It also is the strongest, lightest and only transparent building material. Weighing as little as 3 times that of air, a single inch thickness of this silica-based material has the internal surface area of a basketball court and can protect a human hand from the heat of a blowtorch! Check out some more info on aerogel...
May 5, 1998Theresa
Abbie (Spain)
Azael (Texas, U.S.A.)
Why is space black?
If the sun is like a torch shining its light on the Earth, why is space dark? If the sun is shining its light all the way to Earth and beyond, shouldn't it light up space?
Why does the space in the universe look dark if the sun is always there?
The reason the sky is bright on Earth during the day is that all the molecules of air reflect the light of the Sun like a bunch of little mirrors. In space, however, there are very few molecules, and so the light is not reflected back to us. So, even very close to the Sun, space is black.
April 30, 1998Maggie (Taipei, Taiwan) What is a halation ring?A halation ring is that sort of halo effect that sometimes surrounds objects in photographs or on tv when the light of a bright object extends beyond its boundaries.
April 7, 1998Julian (Victoria, Australia) If we hover above the ground in a helicopter, why don't we see the earth rotate below us?When this happens, the helicopter is actually rotating at the same speed as the Earth, with the atmosphere. This is just like the fact that we don't see the Earth moving under our feet when we are standing on the Earth, or when we jump. Because we are moving at the same speed as the Earth, the Earth appears to be still beneath us.
March 27, 1998Ronaldo (Brasil) I wonder why the outer space is black, at night, and it is not at day ?During the day, the sun emits many light rays toward the Earth. When the light hits the atmosphere, some of the rays come straight through the atmosphere and we see this as the white light from the Sun. Some rays slant through the atmosphere. These rays hit lots of air molecules. The molecules absorb the light, then emit blue light. This is what makes the sky look blue during the day.
At night, very little light is absorbed and re-emitted by the atmosphere, so we see the sky as black, just as we would all the time from space.
March 19, 1998David (Michigan, USA) Why is there no sound in outer space?Humans hear sound when the eardrum vibrates. This vibration is caused by the motion of the air, or the sound waves which are sent from one object and recieved by others. Since the air is necessary to carry sound, and there is no air in space, sound cannot be heard in space.
March 17, 1998Adrienne (Florida, USA) I've heard that glass is actually a liquid, and that this is why the windows in very old houses are thicker at the bottom than the top and why they look warped. Is this true, if not what is the real cause of this phenomenon.This is true. Glass is a very firm sort of liquid and can only be found to flow when a lot of time has past. After a long time, the glass in windows starts to be pulled toward to the bottom by gravity, making the top very thin, and the bottom very thick.
March 4, 1998Michael (New York, USA) Is it true that if you dropped a penny off the Empire State Building and it landed on someone, that it would go straight through them?Well, the penny isn't likely to go all the way through them, but since it would be going about 80 meters per second, it could cause serious injury or death if it were to hit a person on the head.
March 3, 1998Kyle (California, USA) What kind/state of matter is fire? Or is it energy?When an object burns, a chemical reaction is taking place. What we see and feel is the heat and light given off by this reaction, which is releasing energy. Thus heat and light, or fire, is a form of energy.
March 3, 1998Ahuva (Rhode Island, USA) How do you get water from a rock?Rocks usually do not hold any water at all. But, I think this might work with some types of rock if the rock were very porous, meaning it had lots and lots of tiny holes. Then there might be a little bit of water trapped inside those holes. Maybe you could heat the rock until the water inside evaporated and excaped from the rock. This would not produce very much water, though!
March 3, 1998Tawepol (Thailand) What is nuclear fusion? What is osmosis?Nuclear fusion is when atoms fuse together forming a single atom, releasing tremendous heat and light in the process.
Osmosis is the movement of a liquid through a membrane from an area of high concentration to an area of low concentration.
February 11, 1998Jeff (Oklahoma, USA)Does an egg really balance on its end during the vernal equinox or the summer solstice? I'm not sure which time of the year, but I remember an experiment in High School that demonstrated this phenomenon.Many sources will say that at the vernal equinox and the summer solstice, it's possible to stand an egg on its end. Well, this is true for raw eggs (not for hard-boiled ones). However, it is also possible to stand an egg on its end at any other time of the year. Although this feat is not exactly easy, a persistent person can usually succeed given enough time! The only connection between success in standing eggs upright and the equinox/solstice, to my knowledge, is that because of the superstition, many more people try at that time of the year!
February 10, 1998Micah (Washington State, USA)When you blow on the top of a piece of paper, why does the paper go up?When you blow across the top of a piece of paper, you increase the air speed across the top. This has the effect of decreasing the air pressure just above the paper. Since the air pressure just below the paper is now higher than that above, the paper will rise. This is an application of Bernoulli's principle,the same concept behind airplanes! An airplane wing is curved on top and flat on the bottom. This means that the air moving across the top has to travel a longer distance than that moving across the bottom, and therefore must be moving faster. The Bernoulli principle is actually a statement of the conservation of energy.
February 2, 1998Antonio (Florida, USA)One thing I've heard is that there is nothing greater than infinity in the real world, but when we look at numbers we have an infinity of numbers just between 0 and 1, right? But if we count from 0 to 2 we still get an infinite amount of numbers, AND we say the distance is even greater. So there is something greater than infinity in mathematics, infinity itself, right? So, is any object that is traveling at whatever the speed, (in mathematics), going at an infinity speed?This is 'Zeno's Paradox', which says that nature is infinitely divisible. However, this is probably not true. Mathematically, there is an infinity of points between one point and another, no matter how close those two may be. However, physicists believe that Planck's length, which is 1.6x10^-33 cm, is the smallest size possible in our universe of space-time. So, since there really is not an infinite amount of points between two points in nature, it is possible to measure (a finite) speed.
January 8, 1998Micah (Washingon, USA)When a car is traveling at 700 miles per hour, why could it begin to fly?The force of the flow of air underneath the car would be so strong at high speeds that it would completely lift the car off the ground. This is one of the principles behind airplane flight. The Thrust Super Sonic Car (SSC) was designed to break the sound barrier on land. It had to be specially designed to keep it from lifting off the ground as it reached the speed of 764 mph, setting the World Land Speed Record.
December 9, 1997Great (Kentucky, USA)When was the Keck telescope invented?Today Caltech and the University of California operate two Keck telescopes. They premiered in 1995. Both are located in Hawaii. It took 14.4 tons of glass to make the mirrors within just one telescope! These things are big!
December 8, 1997Martin (Michigan, USA)What is a picobar?"Picobar" actually comes from two words. A "bar" is a unit of pressure equal to 14.5 pounds per square inch (imagine 14.5 pounds on an area 1 inch by 1 inch square). "Atmospheres" are a more standard way of measuring pressure--1 bar equals .987 atmospheres. An atmosphere is roughly the atmospheric pressure you'd experience at sea level.

"Pico" is a prefix used in measurements to represent 1 trillionth of something. Therefore, a "picobar" means 1 trillionth of a bar of pressure, or .000000000001 bar. In other words--a very small amount of pressure!

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