Physics experiment: Time for balls of different mass to fall through water?

[scarlettjazz]

So, I have a bucket of water (60cm deep) and I'm releasing balls from the surface. The balls are all the same size and shape but are of different masses (about 10g difference between each). I did some sample tests and got results around 1 second for the balls to sink 60cm. The very short time makes it difficult to get accurate results, but I can see that the heavier balls fall faster.

My question is:

What results should I expect to see? i.e. what is the relationship between the mass of the ball and the time taken to fall through water? Inversely propotional?

I can't figure it out. Mass doesn't affect buoyancy. I'm thinking maybe it has something to do with terminal velocity. Or maybe the distance they fall is too short for terminal velocity to come into play. Is there a simple calculation I can do to try to show what the relationship should be? If terminal velocity is not reached, does the heavier one fall faster because mg is bigger and drag hasn't caught up yet (is it still called drag in water??). If this is the case, would I see an inversely proportional relationship or something more complicated?

Thanks for your help

Density of balls (between approx 1.5-2.5 g/cm^3)

Edited March 17, 2012 by scarlettjazz