Conservation of Momentum

Consider two objects that "interact" or collide or have some effect on each other:

From Newton's Third Law of motion, we know

F₁₂ = - F₂₁

In terms of momentum, this means

F₁₂ = dp₁/dt

F₂₁ = dp₂/dt

so that

dp₁/dt = - dp₂/dt

or

dp₁/dt + dp₂/dt = 0

d ( p₁ + p₂) /dt = 0

dp_Tot/dt = 0

where

p_Tot = p₁ + p₂

That is, the total momentum of the system remains constant. This is Conservation of Momentum

Conservation of Momentum is essentially a restatement of Newton's Third Law of Motion.

Linear Momentum			Impulse
Return to ToC, Ch9, Linear Momentum

(c) Doug Davis, 2001; all rights reserved