# Conservation of Momentum v.s. Conservation of Energy

by 012anonymousx
Tags: conservation, energy, momentum
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P: 6,929
 Quote by Hetware When you hit the wall, the wall experiences a force equal and opposite to the one the car experiences. That force is communicated to the ground. F=ma for the car. Earth get's -F=MA. Or ma=-MA -> A=ma/M. M is huge compared to to you car, so A is tiny. Earth does get a little change in momentum, it's just too small to perceive.
The earth gains all of the momentum lost by the car, but since the earth is massive the change in earth's velocity (angular and linear) is tiny. The total momentum of what can be considered a closed system consisting of the earth and the car remains constant, ignoring any external forces (like gravity from the moon or sun).

As for the loss in kinetic energy with in-elastic collisions, in most situations, it's converted into heat during the deformation process. The relative amount of loss depends on how in-elastic the collision is.

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