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Q & A: steel and rubber balls

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Most recent answer: 10/22/2007
Q:
Will a steel ball or a rubber ball rebounce more on a metal platform? and why?
- mini (age 25)
IIT, Chennai, India
A:
Well, I'd expect them to be very similar in bounciness, as long as the platform is thick and strong (a thin piece of sheet metal may dissipate energy to whatever it is sitting on), and there aren't defects in the balls (like cracks in the steel ball, which can also deform and dissipate energy).

The question becomes which ball will give a larger fraction of the energy needed to squeeze it back when it returns to its original shape on the bounce. Some rubber balls do not give you all your energy back. Squash balls in particular are really bad at bouncing. They deform, but do not return to their original shape quickly enough. Some balls make a big sound when hitting the ground (like a badly inflated basketball). If the steel ball dents or cracks itself or the platform, it can be less bouncy. Little steel balls on big, solid platforms tend to be highly bouncy.

Tom

(published on 10/22/2007)

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