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Why do balls bounce?



While I was throwing bricks at the neighbor's cat the other day, a strange thought occurred to me: why is it that a rubber ball will bounce when it hits the ground bu these bricks do not. To answer that question I turned to my trusty frenemy physics. The reason a rubber ball bounces is because it is made out of an elastic material. This means that, like an elastic band, it can be bent and stretched but still return to its normal shape. When a ball hits the ground (or the neighbor's cat), the surface exerts a force on the ball that deforms it. The kinetic energy of the ball is transformed into elastic energy that is stored in the ball as it is deformed (this process occurs faster than the human eye can perceive). Like a spring, the ball must return to equilibrium, so the elastic energy is converted back into kinetic that translates into upward motion. Of course some energy is lost to air resistance, heat, and sound. Bricks do not have this elastic principle, and if too great a force is exerted on them, the brick will shatter. Their propensity to bounce back to you is why elastic objects are a much better choice for pelting that nefarious cat.


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