Quickie Questions - Physics - Gravity/Light/Magnetism
|Date Answered||Questioner (age, location)||Question||Answer|
|February 21, 2011||George(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.]|
|April 20, 2010||Albie (India)||What is a Light-year||A light-year is a unit of distance. It is the distance that the light travels in a year (assuming it is moving in a vaccum). 1 light year = 9.4605284 ◊ 1015 meters or 9 460 528 400 000 km.|
|March 19, 2010||Marcus (U.S,A)||Is the earth's rotation related to its magnetic field?||I would say the opposite, that the earth's magnetic field is related to its rotation. Magnetic fields are generated by circulating currents of charged particles in a medium that is electrically-conducting. Parker Dynamo Model (developed in the 1960's) describes how the fields are generated and makes possible the calculation of the strength of the field and of how rapidly the field would reverse its polarity. The results obtained from the models match studies of terrestrial paleomagnetism.|
|February 23, 2010||MARY (CA)||falling marbles|
will they fall at the same speed?
put 10 marbles in a plastic bag n seal it,
and 5 marbles in another plastic bag n seal it.
|They would fall at the same rate of change of velocity (same acceleration), if they were falling in a vacuum. In our planet, at sea level, this value is 9.8 m/s2. This means that at any give instant of time they would have the same speed. This fact was first established by Isaac Newton, and has been exhaustively proved many times.|
|January 11, 2010||nishakumari (india)||there is no magnet inside the earth.yet magnetic lines of force exist.how?||In a very simple way, the Earth is a giant magnet. Its hot liquid core contains iron, and as it moves, it creates an electric curent that causes a magnetic field around the planet.|
|January 8, 2010||Jeeva (india)||I think long distance planet have high gravitational force than other planets like earth.my imagine correct or folse tell me sir/madem||The gravitational force that a given mass m1 exerts on an object of mass m2 is proportional to the product of the masses (m1 * m2) and inversely proportional to the square of the distance between the objects.|
|January 6, 2010||Junyi (Australia)||why doesn't earth have no gravity?||It does! It is the force that keep us on its surface!|
|December 16, 2009||terry (suffolk)||the sun moves round the galaxy,|
earth moves round the sun all caused by gravity so is the gravitational pull on earth constant and is it affected by centrifugal force.
|The gravitational force is proportional to the interacting masses (for example, the pair Sun-Earth) and inversely proportional to the square of the distance between them. Because the orbital path is not circular but elliptical, the distance that separates the masses changes with time, and so does the gravitational force.|
|October 19, 2009||cya (india)||if every object has its own gravitation force and small objects attract to objects of greater mass so why doesn't an ant attract towards us (even if our mass is thousand times greater to that of the ant). and will the ant attract towards us if we are in space????||Because our mass is insignificant respect to the mass of our planet, therefore, our gravitational pull on the ant is also insignificant.|
|October 16, 2009||Achal (Karanataka,India)||what is the value of the gravitational constant full [not 6.67*10to the power of -11] i want the simplified value||The value of the gravitational constant = 6.67300 ◊ 10-11 m3 kg-1 s-2 or 0.00000000006673 m3 kg-1 s-2|
|September 30, 2009||Sunil (Madhya pradesh/india)||Does the magnetism of a pole,quantized as electro static charge?||From Maxwell theory, a variable electric field will induce a variable magnetic field, and since static charge are prone to change, so does the magnetic field.|
|September 16, 2009||Raymond (Australia)||My Physics Teacher said as an example "The closer I get the more attracted I become"|
Does it have anything to do with gravity?
|Actually, yes. The gravitational force acts beteween two (or more) objects as a function of the masses of the objects, and the distance between them. The gravitational force is proporcional to the masses, and inversely proportional to the square of the distance between such masses.|
|August 20, 2009||tyler (california)||If a planet were split into identical portions and remained touching but no longer "fused" together, would their combined gravity have the same force on outside objects prior to splitting?||Yes, the center of mass of the system formed by the two halves would stay in the same place, and the combined gravitational force on an external object would remain the same.|
|August 18, 2009||Keith (Florida)||Is there a simple (or even not so simple) equation for finding the gravitational pull on an object based upon its distance from the earths core? such that an object at the equator(roughly 6378.16km from the core) would be pulled down at 9.8m/s(squared) while something in a plane 2km higher (6380.16km) would be pulled down some calculable amount less.||Indeed, the gravitational force exerted by Earth on a given object is calculated by:|
Fg = G [(Me*M)/r2]
G = 6.67300 ◊ 10-11 m3 kg-1 s-2/
Me (Earth mass) = 5.9742 ◊ 1024 kilograms
M = mass of the given object (in kg)
R = Distance, from the center of the Earth, to the object.
|August 18, 2009||Kaitlyn||Is there any other reason about why you donít always see the same stars besides that where you are isnít facing those stars? Does it have anything to do with gravity?||Not really, even the visible stars are very far from us (the closest star is Proxima Centauri, at "just" 4.2 lightyears). Because the gravitational force between two objects is proportional to the product of the masses, and inversely proportional to the square of the distance separating them, it decreases exponencially. At the distances that other stars are, the Sun gravitational field will be very near zero.|
|July 28, 2009||Machabe (SA)||Where does the force of gravity ends?||The force of gravity is proportional to the product of the interacting masses and inversely proportional to the square of the distance between them. So, theoretically, the force of gravity will be zero when the distance between the masses is infinite. In fact, where the force of gravity could be considered zero will depend on the value of the masses.|
|February 25, 2009||Marshall (US)||Does all matter have it's own gravity like cars,me,a computer....etc|
(please note the name of responder)
|Absolutely, all objects have a gravitational field around. The gravitational force between 2 objects is poroportional to the product of the masses of the objects and inversely proportional to the square of the distance between them.|
|February 24, 2009||Vignesh (INDIA)||Earth attracts a body and the body attracts the earth with an equal force. Why then does the body fall towards the earth?||This is explained by one of Newton's formulas: Force = mass * acceleration. If the same force is applied to two bodies with different masses, the acceleration each one obtains is inversely proportional to their masses. Applying this to your question: the acceleration that earth obtains is immensely low due to its huge mass.|
|February 8, 2009||chris (USA)||What is the Suns gravitational pull compared to the Earths?||Your question is way too open to answer. The gravitational force is proportional to the interacting masses, and inversely proportional to the square of the distance between them. To answer your question it would be necessary to know the mass of the second object and the distance to both the sun and the earth.|
|January 20, 2009||Evelyn (AU,NSW)||Why doesn't water fall off earth?||Due to the same reason we walk on Earth: gravity.|
|September 26, 2008||Daniel (Massachusetts)||Do comets have gravitational fields? On the SOHO spacecrafts NASA website video image of the comet McNaught, it appeared to be gigantic, and it seemed to almost collide with Mercury. It was so big compared to Mercury that Mercury looked like a speck of dust next to it. Yet Mercury was undisturbed. Shouldn't Mercury's orbit have been affected by a body so enormous passing so close to it in space?||This is just a perspective appreciation. Mercury is significant more massive that the comet. To answer your question: all bodies of any mass have a gravitational field that is proportional to the product of the interacting masses, and inversely proportional to the square of the distance between them.|
|September 19, 2008||Zhang (Singapore)||will magnetic object lose it magneti power when it is old?||There are two types of magnets, temporal and permanent. Permanent magnets (both natural and artificial) will keep the magnetism for a very long time.|
|September 17, 2008||Toby (Victoria)||Why can't we feel gravity?||We do! That is the force that makes you fall back to the surface after you jump.|
|September 15, 2008||Tim||If the force of gravity on earth is magnetically charged, could these forces be repelled at a small scale. Could there be a polar opposite to these forces at a small scale, like two positivly charged magnets repel each other?||The magnetic and electric fields have poles, but this is not the case for the gravitational field. Gravity forces are always atractive forces.|
|September 10, 2008||Aashita (Punjab, India)||why does earth acts as magnet? for class 7. please atleast give information for 2 pages.||The origin of the Earth's magnetic field is not completely understood, but is thought to be associated with electrical currents produced by the coupling of convective effects and rotation in the spinning liquid metallic outer core of iron and nickel. This mechanism is termed the dynamo effect. Much more information here.|
|September 4, 2008||Sachin (New Delhi, India)||What is the gravitational force in the centre of the earth.||Form the definition of gravitational force we know that it is proportional to the product of the interacting masses and inversely proportional to the square of the distance between them. To calculate the actual value of the force we need to know the value of the masses and the distance between them, and we can plug these values in to the corresponding expression: 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 attraction between two small objects.|
|August 25, 2008||Sisodiya (India)||Gravitational force between earth and moon is F=G*M1*M2/r2 remains same for both i.e. F earth=F moon. then why moon revolves around the earth and not the earth revolves around the moon?||Here you have to keep in mind Newton's 2nd Law of Mechanics (F = m*a). The acceleration a body gets from a force is inversely proportional to its mass. Because the gravitational force between Earth and the Moon is the same, the Moon will get an higher acceleration due to its lower mass, so spinning around the Earth.|
|August 21, 2008||Crystal (CA)||If the distance between the star and planet were three times as great, what effect would this have on their gravitational attraction for each other?||The gravitational force is calculated from: F = G (m1m2/r2) Where: -- F is the magnitude of the gravitational force between the two point masses, -- G is the gravitational constant (6.67 ◊ 10−11 N m2 kg−2), -- m1 is the mass of the first point mass, -- m2 is the mass of the second point mass, -- r is the distance between the two point masses. From this expression we obtain that the gravitational force diminishes with the square of the distance, so, in this particular case, the gravitational force will be 9 times weaker.|
|July 3, 2008||Adam (USA)||A material is magnetized if its magnetic fields face in the _______direction. Would the answer be same or opposite? Thanks||This question is not clear. For example, stroking a magnet over a steel pin from one end to the other will weakly magnetize the steel pin. This is because very large numbers of iron atoms (domains) of the steel become aligned in the same direction.|
|June 30, 2008||eric (Indiana)||if you took a marble and threw it off a cliff would it slow down to the rate of gravity or not||No, it would not slow down. Its downward velocity will increase in about 9.8 m/s every second, which is the value of our planet gravitational acceleration.|
|March 4, 2008||Cathy (United States/Alabama)||Describe how gravity is related to how the world works?||Gravity is the attraction force acting between two bodies. Our solar system is held together by this force.|
|February 4, 2008||sarah (USA)||I heard from my science teacher that according to einstein gravity isn't a force. Is this true?||The concept of gravity field is widely used in physics, and all object inside this field will be under the action of a gravity force proportional to the product of the intearcting masses, and inversely proportional to the square of the distance between them.|
|December 21, 2007||Brandon (CA/US)||Who is the founder of acceleration due to gravity theory and formula?||Isaac Newton's theory of universal gravitation was first publised in 1687, in his book Philosophiae Naturalis Principia Mathematica. The gravitational force can be calculated from: F = G (m1m2/r2) Where: -- F is the magnitude of the gravitational force between the two point masses, -- -- G is the gravitational constant (= 6.67 ◊ 10−11 N m2 kg−2), -- m1 is the mass of the first point mass, -- m2 is the mass of the second point mass, -- r is the distance between the two point masses.|
|July 10, 2007||Ruben (America)||what is lightspeed||Lightspeed is the speed of light. Its value in a vacuum (299 792 458 m/s), is considered the limit speed.|
|July 3, 2007||Meenal (NJ USA)||would Earth loose its gravity if it lost its atmosphere||No. Gravity is a function of the masses and the distance between two objects. Because the mass of the atmosphere is just a minor part of the mass of our planet, the effect on the gravitation would be minimal.|
|June 28, 2007||Heather (?????)||What is the percentage of the earths gravity?????||A free-falling object, i.e. an object which is falling under the sole influence of gravity; has an acceleration of 9.8 m/s2, downward (on Earth). It is known as the acceleration of gravity - the acceleration for any object moving under the sole influence of gravity, and is identified by g = 9.8 m/s2.|
|May 30, 2007||nathan (ohio usa)||how fast does light travel in a nano second?||The light travels in a vaccuum always with the same speed = 299 792 458 meters per second (1 079 252 848.8 km/h). Now, if you want to know how FAR the light travels in 1 nanosecond (one billionth of a second = 0.000 000 001), then it is easy to obtain from the simple expression distance = velocity x time = (299 792 458 m/s) x (0.000 000 001 s) = 0.299 m.|
|January 16, 2007||Gabriella (Jamaica)||can a magnet be used to make another magnet||Yes! it is called "induced magnetism", and it happens when a piece of unmagnetised magnetic material is touched or brought near to the pole of a permanent magnet, becoming a magnet itself.|
|January 10, 2007||Justin (CA)||As you travel through space away from earth, what does the universal law of gravitation say about objects you may encounter that have huge masses?||Because the Universal Law of Gravitation establish that the force of gravity is proportional to the interacting masses and inversely proportional to the square of the distance between them, a close encounter with a huge mass would result in a strong gravitational force.|
|December 20, 2006||Hudson (Texas)||Is light affected by gravity?||Yes, and this effect is used to observe black holes and other massive bodies.|
|November 10, 2006||Kelsey (NY , USA)||What exactly is a light-year and what does it measure?||A light-year is a unit of length used by astronomers. A light-year is defined as the distance that light will travel in a year. If the speed of light is 299,792,458 m/sec (186,282.4 miles/sec) in a vacuum, the distance that light will travel in one year will be:
299,792,458 m/sec x 60 sec/min x 60 min/hr x 24 hr/day x 365 days/yr = 9.454 x 10^15 m/yr (9 454 000 000 000 000 m/yr)
Or expressed in miles:
186,282.4 mi/sec x 60 sec/min x 60 min/hr x 24 hr/day x 365 days/yr = 5.875 x 10^12 mi/yr (5,876,000,000,000 mi/yr)
|January 30, 2004||Elizabeth K.(Ohio, U.S.)||Well, my brother said that there is no gravity in space. I was wondering if this is true or instead of nogravity, there's just micro gravity, because what keeps satllites etc. from flying off into space?||Hi Elizabeth - Good question! There certainly is gravity in space - it's just not as strong as it is on Earth. The force of gravity exists between any two masses, and depends on how massive they are are how far apart they are. The force of gravity is strong close to Earth (or near any other massive body, such as the Sun or other planets), but gets weaker as you go out in space. Gravity is the force that keeps the relatively tiny mass of a satellite from leaving the orbit of Earth. See this page for lots of information about satellites, orbits, and gravity. Thanks for this good question!|
|January 5, 2004||Arunkumar(India)||Does a rocket have to fly with a speed greater than the escape velocity of Earth?||For any object (a rocket, the space shuttle, or satellite being launched to another planet) to escape the Earth's gravitational pull, it must be flying at or above the Earth's escape velocity. Escape velocity is the velocity an object needs to achieve to escape the gravitational pull of another object (like the Earth). Earthís escape velocity is about 11 km/s. This means that if you could throw a baseball at 11 km/s, it could enter into Earth's orbit! One example of this is the recent launch of the Mars rovers. Click here to view the launch sequence that got one of the Mars rovers into space onboard a Delta II rocket.|
|May 9, 2000||Garnet (Canada)||The accepted speed of light is 300 000 km/sec in a vacuum. Considering that it has never been measured anywhere but on Earth, how do we know for absolute sure that the speed of light is in fact a universal constant as opposed to a variable with a constant rate of acceleration.||Scientists have done their best to simulate the conditions in space when doing their experiments. Regardless of the conditions, the speed of light has always been measured at the same speed.
Of course, nothing is absolutely certain. However, there is no proof that we are wrong in our assumption that the speed of light is constant.
|March 6, 2000||Mellisa (New Jersey, USA)||why is the earth not falling out of the sky and could that happen?||The Sun pulls on the Earth: if this were the only thing that were happening, we would have crashed into the Sun long ago! However, something else is happening: the Earth is moving. Since it's moving, the Earth is pulling, away from the Sun. The pul l of the Sun towards itself is the same as the pull away from the Sun that the Earth makes. So, nobody wins, and the Earth stays the same distance away from the Sun!|
|January 20, 2000||Andrew (Pennsylvania, USA)||How do I get two positive magnetic poles to stick together?||Hmmmm, depending on the strength of the magnets you might want to try super glue. Magnetism is a force, and like any other force it is governed by certain laws. One of them is that like poles will always repel each other. Of course, magnets can be demagnetized, and magnetic field reversals on the scale of the Earth have been discovered, but two positive poles will never attract each other.|
|August 27, 1999||Sky (Pennsylvania)||Please explain the difference, if any, between the vibrational frequency and the wavelength of colors. Also, understanding that red has the longest wavelength and purple the shortest, does it take longer for the eye to perceive one color over another and if so would this be the longest or shortest wavelength?||All light has a frequency and wavelength. The two terms are closely related. First, you have to know that light travels in waves, with many "hills", called crests, and "valleys".
The wavelength is the distance between two wave crests of light. The frequency is the number of crests that pass over a given point per second. The two are inversely proportional, which means that as one gets larger, the other gets smaller.
The equation used to relate these two terms is v=c/&, where v is the frequency, c is the speed of light, and & is the wavelength.
From the equation, you may realize that the speed of the color you see doesn't change. All light travels at the same speed, 300,000,000 meters per second!
|July 20, 1999||Saikat (India)||What are gravitational waves? How are they generated?||A gravitational wave (also known as gravitational radiation) is a ripple in the overall geometry (shape) of space and time. All changes in the distribution of mass cause the shape of space and time to adjust. These adjustments show up as ripples which spread out from their source at the speed of light. Gravitational waves are difficult to detect because they carry very little energy.|
|July 9, 1999||Amy (California)||How do scientist measure the speed of light and what is the speed of light?||The first accurate experimental measurement of the speed of light was preformed by Albert A. Michelson early in the 20th century. He used a complex system of rotating mirrors on one mountain and fixed mirrors on another mountain a known distance away. The most accurate modern measurements have been done using lasers in a vacuum. The speed of light is known as c and has a value of 2.997924*10^8 m/s.|
|July 7, 1999||Kevin (California)||Why doesn't the Moon fall down?||Good question Kevin! The moon is actually falling all the time. It's just going so fast it never catches up to the Earth. This never ending falling is called orbital motion.|
|July 1, 1999||Joe (Florida)||What is the maximum velocity a person can reach while falling?||Terminal velocity for a sky diver on Earth is about 190km/hr (118mi/hr). Objects that have lots of air resistance in relation to their mass (like a feather) have a much lower terminal velocity.|
|June 22, 1999||Teressa (Alaska)||If light is not made of matter, how can gravity effect it? How can it be sucked into black holes if it has no mass?||Photons of light are affected by gravity because gravitational fields change the shape of space-time. The curvature of space-time causes a beam of photons to bend. A black hole is very dense, and has a very strong gravitational field. This warps space-time greatly, bending the light inward. In fact, the light is bent so severely that it cannot escape.|
|May 25, 1999||Heather (Malaysia)||I wanted to know how a concave mirror works. When I stand away from the mirror, the object in it looks upside-down. But if I'm really close to the mirror, the object is upright. Why?||A concave mirror works by converging light. This means that all the light that hits the mirror is angled towards one common point, called the convergence point. At this point, the path of light intersects, which means that the "reflection" of the bottom part of the letter crosses the "reflection" of the top of the letter. This makes the letter appear upside-down. However, if you are standing really close to the mirror, you may be in between the point and the mirror. In this case, the light hasn't had time to intersect, so the object appears right-side up.|
|March 17, 1999||Angela (Alabama, USA)||How does a light year measure to our year? Is a light year equal to one of our years? If not what is the difference?||A light year is not actually a measurement of time, it's a measurement of distance. A light year is the distance light travels in one year. Since light travels at the speed of 186,000 miles per second, that means that in one year, light travels a distance of approximately 5,870,000,000,000 miles.|
|January 22, 1999||Tyler (Ontario, Canada)||How does a magnet work?||This page should help.|
|January 6, 1999||Michael||What is the effect of temperature on magnetism?||An increase in temperature will give a decrease in magnetism. This is because the magnetic particles vibrate more as the temperature increases, and this destroys their alignment.|
|December 21, 1998||Cary||Is it true that if you drop a magnet it will lose its power? I am afraid to put my magnet down now.||Objects are made of little tiny magnetized areas called domains. In a magnet, these little areas are nearly all lined up to point in the same direction. The reason knocking a magnet very hard decreases its magnetism is because you knock some of the domains out of alignment, causing them to point in other directions. This weakens the magnetic field of the magnet. However, you would have to drop the magnet very, very hard to cause a noticeable difference in the strength of your magnet. So, there's no need to worry about putting it down for a while!|
|December 21, 1998||Lyn||Does magnetism work in space?||Yes, magnetism does work in space. The Earth's magnetic field extends into space a long way, and Jupiter's is absolutely huge! In order to measure the planetary fields, Voyager had instruments calledmagnetometers onboard.|
|October 28, 1998||Becky (Auckland, New Zealand)||Why is there no gravity in space ?||There is gravity in space. However, the amount of gravity you feel depends on how far away from the object you are. Since when you are in outer space you are far away from any large object, you don't feel as much of a gravitational pull from it.|
|October 21, 1998||Cody (South Carolina, USA)||My question is since light goes at a set speed then if we made an object that would go faster than light and had the capability to look back upon the earth, wouldn't it be able to look back into the past since the recent light hadn't reached it yet?||Theoretically, yes! This is the primary principle of time travel. The closer to the speed of light we are moving the slower time slows. So theoretically, someone traveling at the speed of light would experience time stopping, and someone traveling faster than the speed of light would experience time moving backwards.|
|October 13, 1998||Will (California, USA)||Are gravity and light (energy), two sides of the same thing? is gravities pull as fast as lights push? are there mathematical relationships?||Close. But light is a form of energy. This means that all light is energy but not all energy is light. Energy can also be in the form of mass. Both light and gravity have a gravitational pull, which is currently thought to move at the speed of light .|
|October 13, 1998||Peter (Vancouver, Canada and Arizona, USA)||When the Shuttles were first launched there were references to ZERO Gravity. Now it is usually termed MICRO gravity. Why ?||Microgravity is the condition of near weightlessness that occurs when an object undergoes free fall,or is placed at a very great distance from massive objects like the Earth. It is now called microgravity because it is not really zero gravity, just ve ry small. (You would have to be infinitely far from other objects in order to experience zero gravity.)|
|June 22, 1998||Sunshine (Michigan, USA)||What keeps the planets in orbit?||The Sun's gravity is what keeps the planets in orbit. Without gravity acting as the centripetal force (the pull toward the center of the Sun), the planets would move off in a st raight line into outer space!|
|June 22, 1998||Robert (Michigan, USA)||If there was ever a space wheel (large space station shaped like a wheel) in the future will it have its own gravity? Does it matter if an object in space be turning in order to have gravity such as the moon?||I've often heard the estimate that in order for a space wheel to 'create its own gravity', it would have to be over two miles in length. The 'gravity' would actually just be centrifugal force created by the wheel spinning. The centrifugal force would push humans and all other objects outward, so that the outward walls of the wheel would become the down direction (simulating gravity). However, this type of space wheel is not very practical because it has to be so huge to work!|
The Moon, and the Earth for that matter, do not have to be spinning for them to have gravitational pull on other objects. It is their mass, not their spinning that creates this force.
|April 14, 1998||Julian (Victoria, Australia)||I read recently that light travels slower through water, is this true?||No. The speed of light is constant (186,282 mi/s), and never varies. The reason it takes longer to pass through some physical mediums is because of refraction. This occurs when light is absorbed, then re-emitted, which takes time. This causes the speed of light to seem slower.|
|April 7, 1998||Cara (Rhode Island, U.S.A.)||Why is there less gravity in space?||The amount of gravity you feel depends on how far away from the object you are. Since when you are in outer space you are far away from any large object, you don't feel as much of a gravitational pull from it.|
|April 7, 1998||D (Singapore)||Are gravitational forces instantaneous? or nearly so?||The current belief about gravity is that it moves at the speed of light, or nearly so. So, it is not instantaneous, but it is very fast.|
|April 2, 1998||Greg (U.K.)||If the sun 'magically' disappeared would the Earth continue in its orbit around where the sun was for another 8.5 minutes: does gravity travel at the speed of light?||The current theory is that gravity does travel at the speed of light, although it has never been proven, so I suppose the Earth would continue in its orbit for 8.5 minutes. However, for the Sun to "magically" disappear it would have to violate all pr incipals of physics, so this will never happen.|
|March 27, 1998||Antonio (Florida, USA)||Are photons a kind of energy or of matter?||Photons are the particles which make up light. They are very strange. When they are not moving, they have no mass. However, usually they are moving at the speed of light. When they are moving, they have kinetic energy--the energy of movement. Hav ing this energy means they can feel the effects of gravity. Photons are particles which have all of their mass converted to energy. So, photons are sort of both energy and matter.|
|March 24, 1998||Giulio (Italy)||What would happen if an object goes faster than light?||We have no evidence of anything ever being able to go faster than the speed of light, and so through predictions and observations, it appears that Einstein was correct, and nothing can go faster than the speed of light.|
|March 19, 1998||Dima (USA)||Is thought faster than light?||The speed of thought is very hard to measure. However, although thought moves very fast, it is moving very small distances (just around your brain). This makes it seem extremely fast. Light, on the other hand, moves millions of miles per second. So, light is still the fastest object.|
|March 3, 1998||Connor||Why doesn't the moon keep on going in a straight line into the universe? And can you tell me how it was proven(if it has) that the earth doesn't orbit around the moon.||The reason the moon doesn't continue out into the universe is that the Earth exerts a pull on the moon, which keeps it orbiting the Earth. Since the Earth is so big compared to the moon, it pulls the moon toward it. In a sense, the moon is falling towards the Earth, but since the moon is also moving forwards, it ends up going around and around the Earth.|
The reason we know the Earth doesn't orbit the moon is that the Earth is so much bigger than the moon. The gravitational pull of the moon isn't enough to pull the Earth into its orbit.
|February 6, 1998||Joe (Alabama, USA)||Is everything in space weigthless, if so, then could it be possible to move a planet with a certain device from Earth? Thus you can move planets from orbit to orbit by breaking their gravitional pull. Is this possible?||I don't think it is possible! You see, everything in space isn't weightless! The planets don't just float out in space, drifting here and there. Because of the Sun's strong gravitational pull, the planets have been in fixed orbits for a long time...and it would take something unusual to move a planet out of its orbit! Take Mars for example. Its mass is 6.42e23 kg (that's about a tenth of the mass of the Earth). It would take something pretty big to move Mars out of its orbit (bigger than anything we could build here on Earth). Perhaps if another planet crashed into Mars, then it would get thrown out of its orbit...|
|January 30, 1998||Lacey (Iowa, USA)||When you spin in circles, you can't seem to keep your arms to the side of your body. So why don't we float off the Earth into space since it is spinning too?||The spinning of the Earth is not actually what causes us to stick to it. Gravity is the attractive force that keeps us from flying off into space. This attraction is present between all things which have mass. Since the mass of your body and arms is small (compared to astronomical objects), you don't notice this attraction. However, since the Earth is so huge compared to your body, it attracts you very strongly. This is why we are not little satellites orbiting Earth!|
|January 21, 1998||Antonio (Florida, USA)||Do all objects in space have mass?||No. You can think of light as a particle (or object) and light is massless. That's what allows it to move at the speed of light!|
|January 20, 1998||Ed||I recently saw a PBS show about the space station to be built, and cannot understand why, with all the knowledge about how weightlessness adversely affecting the body, it is not designed to spin to create false gravity?||I've heard the idea mentioned before...if you could get the space station to spin, then the centrifugal force created by the spinning (the same force that pulls you outwards on a merry-go-round) could be used to simulate gravity. Gosh, from what I remember of the idea, the space station would have to be a least two miles long for this to work. And right now, that's just not feasible because of the money it would take to get that much hardware into space!|
|January 20, 1998||Russ (Tennessee, USA)||I recently saw a PBS show about the space station to be built, and cannot understand why, with all the knowledge about how weightlessness adversely affecting the body, it is not designed to spin to create false gravity?||Why is the speed of light constant regardless of the frame of reference (even if you're moving at half the speed of light and I'm standing still, and you shine a flashlight my way...)? Well, it just is. It is an experimental fact of life that we have to deal with. You see, movement on our behalf (or changes in the frame of reference), don't change the speed of the electromagnetic disturbance we call light. The only thing that does affect the speed of light is the refractive index of a material which could "slow" down the light. For example, in glass, light travels 1.3333 times slower than through empty space or the speed of light is 225,000 km/s through glass.|
|January 8, 1998||Andrew (Iowa, USA)||Why does pop fizz when you shake it?||The bubbles in soda pop are caused by a gas called carbon dioxide, which is bubbled through the drink. When you shake it, you release some of the bubbles, which causes the drink to fizz. When pop goes flat, it is because all the bubbles have escaped the drink, leaving only the flavored liquid.|
|January 5, 1998||Jackson (Melbourne, Australia)||How does gravity work?||We are not sure exactly what gravity is, or how it works. We can, however, observe its effects. Gravity is the attractive force between two objects. The bigger the object, the harder it pulls. Also, the farther away it is, the smaller the pull.|
|December 30, 1997||Antonio (Florida, USA)||I've heard some people say photons don't have mass, but if they wouldn't have mass how could they interact with matter. Do they? How about neutrinos?||Not all objects have mass. Photons of light, for example, do not have mass.Neutrinos are also believed to be massless. But just because something doesn't have mass doesn't mean that it cannot interact with other objects. Gravity, which depends on the mass of an object, is only one force through which matter interacts. There are three other known forces, including electromagnetism, the weak force and the strong force. For example, light can interact with other particles through the electromagnetic force. Neutrinos are involved in interactions where the weak force is important, such as the decay of atomic nuclei.|
|December 8, 1997||Carole (New Jersey, USA)||How many miles are in a light year?||Since light travels at the speed of 186,000 miles per second, that means that in one year, light would travel a distance of approximately 5,870,000,000,000 miles. That's roughly 6 million million miles!|