Conservation of Momentum

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Things change. If you are willing to wait long enough, just about everything changes. Physicists have found, however, that there are a very few quantities that, under the right conditions, don't change. They have also found that an understanding of these conserved quantities can be very powerful. Momentum is one of these quantities. Under the right conditions, the amount of momentum in a system does not change.

What conditions? If you look carefully at the impulse-momentum equation,

Impulse-momentum equation

it becomes apparent that:

Conservation of Momentum

This is one way to state the Law of Conservation of Momentum. It follows directly from the impulse-momentum equation, which is, essentially, Newton's Second Law. (Here is a more direct way to get the Law of Conservation of Momentum from Newton's Second Law.) However, the Law of Conservation of Momentum is much more powerful than Newton's Second Law. No experiment to date has shown a violation of the Law of Conservation of Momentum. It applies to objects moving very fast or to objects inside the atom - both places where Newton's Second Law fails.

In addition to its universal applicability, the Law of Conservation of Momentum is a very powerful, and maybe even better, simple and straightforward way to explain the physics of many situations.

last update November 28, 2007 by JL Stanbrough