Conservation of Momentum

Discussion

start

Start with Newton's third law of motion, toss in the impulse-momentum theorem, and see what happens.

+F1 =  F2
+F1Δt =  F2Δt
+m1Δv1 =  m2Δv2
p1 =  −Δp2
+(p1 − p10) =  −(p2 − p20)
p1 + p2 =  p10 + p20
p =  p0

Momentum is conserved. The total momentum of a closed system is constant.

1668: John Wallis suggests the law of conservation of momentum

recoil

The symbol p may be used for momentum because it is the mirror image of the letter q. Some people use p to represent the momentum of one object and q to represent the momentum of the other object in a recoil situation. A clever way to write Newton's third law of motion is like this…

+p = −q

action is equal and opposite reaction

collisions

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