Experiment with rolling balls-Why were results different at different heights?

[Blou]

Experiment with rolling balls--Why were results different at different heights?

1. My son's science fair data is hard to understand. In a speed test rolling four balls down a ramp at 10" and 21" height the results were not consistent between the two heights. At the 10" height the balls with the most density had faster times down the ten foot ramp. (pool ball, gulf ball, basketball, foam ball) At the 21" height the balls won according to their mass. (basketball, pool ball, gulf ball, foam ball) We figured that the 10" data was due to the moment of inertia but we are not able to figure out the reason it switched at the 21" height.

2. We are not able to work with many equations at his level.


3.We are researching and wondering if the height change made such a difference because of the critical angle or because of the change in slipping or rolling? We are over our heads but it would be great to explain his findings in some way.

 

[genericusrnme]

Is this a question for a book or are we talking about an irl son here?

I'm going to go out on a limb here and say friction of some kind is behind your problems..
If there's a problem it's almost always friction