• Question: Why are some objects bouncy?

    Asked by anon-267549 on 16 Nov 2020.
    • Photo: Bradley Young

      Bradley Young answered on 16 Nov 2020:

      This could be for 2 reasons:
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      For something squashy like a tennis ball or a rubber ball, it’s because of a property called elasticity. The force of dropping it elastically deforms the atoms or molecules in the object. These atoms/molecules then want to return to their original position and this produces a force pushing the object away from the floor.
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      The other reason is when something isn’t squashy (like a ping pong ball) and then we use newton’s 3rd law of motion. This tells us that the floor must exert a force on the object and so if the floor doesn’t move then the object must bounce.
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      There’s a great experiment for this where you can cool a squash ball down really cold and it transforms from the first explanation to the second explanation.

    • Photo: Jesse Dykes

      Jesse Dykes answered on 17 Nov 2020:

      What an excellent question! I’ve discussed with some colleagues and we’ve gotten an answer.

      So materials are made up of atoms, as you know. These atoms are joined together into molecules. In some materials like metals and rocks, all of the atoms are bonded together into one big molecule and it’s hard to break that molecule up. In others like plastics, they’re joined together into long chains of atoms, which are tangled together, and if you apply force the chains can slide over each other and shift around and move out of the way. In some plastics like rubbers, there is an equilibrium position for the molecules to be in where they have the least energy. So if you put in energy by applying force, the rubber will release that energy again afterwards as it returns to equilibrium. It will do that by applying force to whatever pushed it

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