MDCAT Physics · Physics · Force and motion. The idea in plain words, the rules to remember, the mistake to avoid and a worked example, written and checked by Mega Lecture.
Newton's laws link force and motion. A body keeps its state of rest or uniform velocity unless a net force acts on it. This resistance to change is inertia, and it depends only on mass. A net force gives an acceleration in its own direction. Forces always come in equal and opposite pairs that act on two different bodies.
Momentum is mass × velocity and is a vector. A force acting for a time changes the momentum; force × time is called impulse. A longer time for the same change of momentum means a smaller force.
When no external force acts on a system, its total momentum stays the same in every collision. Kinetic energy is conserved only in an elastic collision.
Students forget that momentum is a vector. When a body reverses direction, one velocity must be negative, so the change in momentum is larger than either momentum alone.
Answer: 750 N, in the direction the ball leaves the bat.
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