Q:

which ball falls fastest, a basketball, or tennis ball??? heavy ball vs. lighter ball

- alan (age 9)

citrus heights

- alan (age 9)

citrus heights

A:

Alan,

Great question. As it turns out, the force of gravity tries to make everything accelerate downward at EXACTLY the same rate, no matter how light or heavy it is. This means that if you dropped a basketball and a tennis ball at the same time (from the same height) they will hit the ground at the same time (try it!).

Is this true for all objects? If you drop a feather and a rock at the same time, you know the rock will hit the ground first and the feather will fall much slower.

This does NOT mean that what I said above is wrong. The problem with dropping stuff near the surface of the earth is that gravity is not the only force acting…there is also air resistance. Air tends to make stuff fall slower, especially light objects, which is why the feather hits the ground last. Since tennis balls and basketballs are quite heavy, at least compared to feathers, we don't easily notice the effect of air resistance on these (although it's still there).

If there were no air, all objects would fall at exactly the same rate. In other words, if you went to the moon (where there is no atmosphere) and dropped a feather, a rock, a tennis ball and a basketball, they would all hit the ground at the same time.

Hope this helps.

MS

Great question. As it turns out, the force of gravity tries to make everything accelerate downward at EXACTLY the same rate, no matter how light or heavy it is. This means that if you dropped a basketball and a tennis ball at the same time (from the same height) they will hit the ground at the same time (try it!).

Is this true for all objects? If you drop a feather and a rock at the same time, you know the rock will hit the ground first and the feather will fall much slower.

This does NOT mean that what I said above is wrong. The problem with dropping stuff near the surface of the earth is that gravity is not the only force acting…there is also air resistance. Air tends to make stuff fall slower, especially light objects, which is why the feather hits the ground last. Since tennis balls and basketballs are quite heavy, at least compared to feathers, we don't easily notice the effect of air resistance on these (although it's still there).

If there were no air, all objects would fall at exactly the same rate. In other words, if you went to the moon (where there is no atmosphere) and dropped a feather, a rock, a tennis ball and a basketball, they would all hit the ground at the same time.

Hope this helps.

MS

*(published on 10/22/2007)*