Momentum has to be conserved

  • Thread starter HiPPiE
  • Start date
  • #1
20
0

Main Question or Discussion Point

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:
mv=mv
(1)10=v(51)
v=10/51
KE1=.5(1)(10)^2=50j
KE2=.5(51)(10/51)^2=.98j

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?
 

Answers and Replies

  • #2
167
0
Think about friction, sound all other waves that have some energy
 
  • #3
Meir Achuz
Science Advisor
Homework Helper
Gold Member
2,177
69
HiPPiE said:
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:
mv=mv
(1)10=v(51)
v=10/51
KE1=.5(1)(10)^2=50j
KE2=.5(51)(10/51)^2=.98j

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?
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.
 
  • #4
Danger
Gold Member
9,607
244
Meir Achuz said:
which gives you a warm feeling because the batter is out.
:rofl:
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.
 
  • #5
167
0
Friction - i meant air resistance, no distances were given
 
  • #6
20
0
Ok, I see. Makes sense...

Oh and thanks :)
 

Related Threads on Momentum has to be conserved

  • Last Post
Replies
2
Views
1K
Replies
23
Views
3K
Replies
12
Views
3K
Replies
48
Views
7K
  • Last Post
Replies
8
Views
2K
  • Last Post
Replies
2
Views
540
Replies
5
Views
3K
  • Last Post
Replies
5
Views
2K
Top