Physicopoeia

φυσικοποιΐα
THINGS I WISH I'D KNOWN WHEN I STARTED TEACHING PHYSICS

Deriving Conservation of Momentum

As far as I can remember, I spent my schooldays in unconscious ignorance of the fact that the law of conservation of momentum can be derived quite easily from Newton's Laws of motion. I suppose I must have assumed it was a separate piece of Physics, probably empirically derived like Conservation of Energy was, though I doubt I gave it much thought. Since conservation of momentum can be conceptually demanding for pupils who are less intuitively mathematical, I often find it helps to show exactly where we get conservation of momentum from. Added to that is the importance of showing more capable pupils that rules like this don't just spring out of thin air. Here's a derivation: