Free fall. ball vs lead

Can someone explain why a tennis ball will fall slower then a lead piece of the same size?

my idea is that it has more air resistance because of the shape, but is that right?

I know mass doesnt affect the acceleration so thats not the reason right?

thanks in advance for any help given. :smile:

Reply 1

teachercol

Mass has no effect if air resistance is negligible - but that is not the case here.

The air resistance of the two is the same - but the weight of the lead is much greater.

This means that the resultant force downward is much bigger for the lead - so its acceleration will be bigger. (and its terminal velocity is higher if they fall far enough)

Reply 2

James

I'm not convinced. Could you go over that in more detail please?

Reply 3

Robob

jamesgurung

I'm not convinced. Could you go over that in more detail please?

Right, in order to find the acceleration, you resolve downwards:

mg - F = ma

a = g - F/m

Where m is the mass, F is the force of air resistance and a is the acceleration.

Since they are the same shape, F is the same for both.

However since the mass of the lead ball is greater, F/m is smaller, hence a is greater and so it falls 'faster' than the tennis ball.