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Asked by Bethyboo to Alice, Bose, Christian, Emma, Steve on 16 Mar 2016.
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Steve Marsden answered on 16 Mar 2016:
The heavier an object is, the larger a force you need in order to accelerate it. Also, the heavier an object, the more gravity pulls it down. These two concepts cancel out, and make all objects fall at the same rate… in a vacuum.
In air, air resistance must be considered. This resistance applies a force based on the shape of the object. So a light and heavy object of the same shape will be subject to the same force trying to slow them down. But this force is smaller compared to the mass of the heavy object, so has a smaller effect. Thus the heavier object isn’t slowed down as much, and so falls quicker.
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Emma Dean answered on 17 Mar 2016:
They don’t! Everything on earth falls at the same rate. This is because gravity is the same everywhere on earth. Gravity is the only downwards acting force, so if the same force acts on everything in the same way, then everything falls at the same speed.
On earth we have an atmosphere. When objects fall through the air there is a force that acts in the opposite direction called air resistance. An example of this is if you drop two A4 sheets of paper at the same time, except one is scrunched up into a ball. The scrunched up ball will fall in pretty much a straight line to the ground first. The flat sheet of paper will drift down slowly because it has a larger surface area than the ball, so more air stops it from falling down. If you were to do the same experiment in a vacuum (where there isn’t any air) then both pieces of paper would fall at the same time. A feather and a bowling ball would also fall together and hit the ground at the same time in a vacuum.
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