- #1
Veni2K
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Hi everyone!
I recently read a problem in a university textbook that read about an inelastic collision. There are two pucks (hockey?) on the ice, one at rest. Both the same mass, one approaches the other at a velocity and when they collide they stick together and both move off with a velocity of v/2 as the conservation of momentum predicts. When you calculate the Kinetic energy of the resulting body, it seems that half the energy has been lost somewhere.
The answers I've seen are the energy has been lost to heat and thermal energy in the surroundings. I was just wondering how an equation based on mass and velocity (conservation of momentum) could predict energy being lost as heat, how does the equation have knowledge of those concepts? Perhaps there's a flaw in the way I'm asking the question but I think my brain is primarily looking for an explanation as to the mechanism of this energy loss and once examined, how it occurs so that it's always in keeping with the conservation of momentum. Am I making sense at all? I guess I'm looking for the cause... for the effect :)
I did in my thinking come up with a nice analogy for some people who may be struggling to understand how momentum is conserved in some collisions when kinetic energy is not, even though they both are dependant on velocity. The way I reasoned it is like this, Imagine you have a whole vase or other such object. Imagine you smash it to pieces. Even though you have smashed it up, you've still got all the pieces of the whole, you've not really lost it, you can account for them all. In my head this analogy helped me to at least get a handle on viewing the conservation of momentum as a collective process, rather than just focussing on the changes on a particular particle.
Maybe all or some of this logic is wrong, just thought i'd share where I'm at in case someone has any insight into why I might be stuck, or how I can conceptualise what really happens in a collision where energy is lost and how this magic conservation of momentum can predict heat energy transfer when it doesn't seem to know of anything apart from mass and velocity of the objects involved.
Thanks! (Sorry for the long post)
Veni
I recently read a problem in a university textbook that read about an inelastic collision. There are two pucks (hockey?) on the ice, one at rest. Both the same mass, one approaches the other at a velocity and when they collide they stick together and both move off with a velocity of v/2 as the conservation of momentum predicts. When you calculate the Kinetic energy of the resulting body, it seems that half the energy has been lost somewhere.
The answers I've seen are the energy has been lost to heat and thermal energy in the surroundings. I was just wondering how an equation based on mass and velocity (conservation of momentum) could predict energy being lost as heat, how does the equation have knowledge of those concepts? Perhaps there's a flaw in the way I'm asking the question but I think my brain is primarily looking for an explanation as to the mechanism of this energy loss and once examined, how it occurs so that it's always in keeping with the conservation of momentum. Am I making sense at all? I guess I'm looking for the cause... for the effect :)
I did in my thinking come up with a nice analogy for some people who may be struggling to understand how momentum is conserved in some collisions when kinetic energy is not, even though they both are dependant on velocity. The way I reasoned it is like this, Imagine you have a whole vase or other such object. Imagine you smash it to pieces. Even though you have smashed it up, you've still got all the pieces of the whole, you've not really lost it, you can account for them all. In my head this analogy helped me to at least get a handle on viewing the conservation of momentum as a collective process, rather than just focussing on the changes on a particular particle.
Maybe all or some of this logic is wrong, just thought i'd share where I'm at in case someone has any insight into why I might be stuck, or how I can conceptualise what really happens in a collision where energy is lost and how this magic conservation of momentum can predict heat energy transfer when it doesn't seem to know of anything apart from mass and velocity of the objects involved.
Thanks! (Sorry for the long post)
Veni