Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Momentum has to be conserved

  1. Aug 23, 2005 #1
    I suppose this sounds a little silly, but:

    Momentum has to be conserved, but often at the cost of some kinetic energy. For example, if someone throws a 1kg mass at 50kg person at 10 m/s, he catches it:

    Heat is thus created, but my question is: where? I suppose in this situation it would be in the glove... but how exactly does that heat come about? Heat is, I guess, kinetic energy on a smaller scale (moving particles). How do these particles begin to move?
  2. jcsd
  3. Aug 23, 2005 #2
    Think about friction, sound all other waves that have some energy
  4. Aug 23, 2005 #3

    Meir Achuz

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    There is not much friction here. The ball striking the glove causes it to vibrate. This vibration quickly degrades into a random vibration of the molecules in the glove, which raises their internal energy
    (U in thermodynamics). This increase in U raises the temperature of the glove. Heat is the transfer of this internal energy from the glove to your hand, which gives you a warm feeling because the batter is out.
  5. Aug 23, 2005 #4


    User Avatar
    Gold Member

    I would propose further that some of the muscular effort used to maintain the glove in position when the ball hits it produces heat in the catcher and could be considered part of the system.
  6. Aug 23, 2005 #5
    Friction - i meant air resistance, no distances were given
  7. Aug 24, 2005 #6
    Ok, I see. Makes sense...

    Oh and thanks :)
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook