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Can you explain gravity? How come two balls hit the ground at the same time? - Windows to the Universe

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# Can you explain gravity? How come two balls hit the ground at the same time?If you hang a one liter bag of formula from a six foot pole and another one liter bag of formula from a three foot pole. Will the bags empty at the same rate ??

#### Gravity is defined as an attraction between two objects. Everything in the Universe with mass has gravity, but only large objects like planets or moons have a gravity strong enough to affect other things. Everything falls to Earth at the same speed, regardless of the mass. Isaac Newton developed his Second Law, which states that the force exerted on an object is equal to its mass multiplied by its acceleration. In the case of Earth's gravity, we say that the amount of force the Earth uses to pull an object down is equal to the object's mass times its acceleration. So why don't heavier objects fall faster? Imagine a car and a rock falling to Earth. The car has a greater mass, so it has a greater attraction to Earth than the rock. However, because it is so large, the Earth has to pull harder to get it down. Basically, this means that all objects fall at the same speed, because the mass the object and the force applied by Earth change at the same rate. Scientists discovered that the acceleration of gravity is about 9.81 meters per squared seconds. Unfortunately, it is difficult to test this theory at home because other influences like air can affect the speed of the object. Although if you drop a ball and a feather in an air tight tube, you will see that both fall to the ground at the same time! In the case of two bags of formula, there will actually be a very slight difference in the emptying speed. The farther away an object is from Earth, the smaller the gravitational pull. However, a small distance such as 3 feet is too small to make a difference. If one bag was at 3 feet and another at 3 miles, the bag at 3 miles would not empty as quickly!

Submitted by Danielle (California, USA), Matthew (Ontario, Canada), Adrienne (Michigan, USA), G.S.(New Jersey, USA), K(Chennai, India)
(May 18, 1999)

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Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part is sponsored in part through grants from federal agencies (NASA and NOAA), and partnerships with affiliated organizations, including the American Geophysical Union, the Howard Hughes Medical Institute, the Earth System Information Partnership, the American Meteorological Society, the National Center for Science Education, and TERC. The American Geophysical Union and the American Geosciences Institute are Windows to the Universe Founding Partners. NESTA welcomes new Institutional Affiliates in support of our ongoing programs, as well as collaborations on new projects. Contact NESTA for more information.