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B Why is it quieter to lower your hand when you catch a falling ball?

  1. Jun 7, 2017 #1
    If there is a ball falling from a height due to gravity, and you keep your hand still and let the ball fall onto it, it stops suddenly and makes a loud noise. However, if you lower your hand as you catch the ball, like when a cricketer catches a fast moving ball, the catch is almost silent. I understand that in the second scenario, the force exerted is lower because the change in momentum of the ball occurs in a longer time. However, since there is the same amount of GPE being transferred during the collision, why does the second one have a lot less sound energy being released than the first?
     
  2. jcsd
  3. Jun 7, 2017 #2

    davenn

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    you answered your own question
    what don't you like about that answer ?
     
  4. Jun 7, 2017 #3

    russ_watters

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    What causes the release of sound energy? It kind of looks to me like you answered your own question when describing its background!
     
  5. Jun 7, 2017 #4
    I can't seem to understand the relationship between the force and the energy. How can the second one have a lesser force and therefore less sound, but then the same amount of energy still get lost? Where does the energy go if it isn't sound or kinetic or GPE, and I can't imagine it being heat or anything else?
     
  6. Jun 7, 2017 #5

    russ_watters

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    You still answered that, though didn't go into the details:
     
  7. Jun 7, 2017 #6
    Is it stored in your arm as if it were a spring, and if so, why doesn't it stretch back afterwards?
     
  8. Jun 7, 2017 #7

    russ_watters

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    Well, kind of, but no; you dont let it. You have control over your muscles and making them do stuff consumes energy.
     
  9. Jun 7, 2017 #8
    So isn't the energy used even more then... Why do you have to use energy to catch it but then less energy is released afterwards?
     
  10. Jun 7, 2017 #9

    russ_watters

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    All of the kinetic energy of the ball is absorbed by one thing or another (almost all by your arm) in both cases. How much energy you need to apply to your arm to make that happen is a matter of biology, not physics. It isnt actually clear to me which requires more.
     
  11. Jun 7, 2017 #10
    OK, so to sum up, the force when moving your hand down is lower which makes a quieter sound, but the work done in both situations is equal and the loss of kinetic energy into the arm is biology so not part of the problem. Thanks.
     
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