GCSE Science/Newton's second law

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Newton's Second Law[edit]

Momentum[edit]

A motion of a body is described by its momentum. Momentum is the product of a body's mass and its velocity. Momentum has both magnitude and direction. Newton showed that bodies only change their motion when a force is applied, Newtons first law. The change in the momentum is equal to the applied force.

Derivation of Newton's second law[edit]

Consider a snooker ball of mass m moving with a velocity v1. The ball hits the cushion and bounces off, it now has a velocity v2. The change in momentum is mv1mv2 = m(v1v2). The change in velocity is the acceleration, and so the change in momentum and hence force F is mass times acceleration, F = ma. Thus Action and Reaction are equal but opposite in direction.