Why is momentum conserved in collisions?

Question

please only answer if you know what you are talking about.
=]

Answer 1

The conservation of momentum can be shown to be a mathematical consequence of Newton's 2nd Law (F=ma).

So you could say that momentums is conserved "because" F = ma.

On the other hand, you could also ask, "Why does F = ma?". In fact, the modern interpretation is that conservation of momentum is more "fundamental" than Newtons' 2nd law; that is, nowadays physicists say that Newtons' 2nd Law is a mathematical consequence of the conservation of momentum, rather than the other way around.

So, the "why" is kind of a philosophical question. Momentum is conserved because that's the way the world works.

Answer 2

this is actually one of the fundamental facts of nature - some things are conserved... momentum, angular momentum, mass-energy, charge. (maybe some others that don't spring immediately to mind.)

so if you are working in a closed system - which means there's no interaction with the outside world - momentum must be conserved in your system.

which means it will be conserved in collisions

hth