Newton's Laws of Motion
Why bodies stay still, speed up, or push back — the three rules that run all of mechanics
Big idea: In grades 7–8 you learned to describe motion — position, velocity, acceleration. Newton's three laws tell you the cause of motion: a body changes its velocity only when a net force acts on it, the change is set by F = ma, and every push comes with an equal push back. Everything from a falling apple to a rocket over Baikonur obeys these same three rules.
By the end of this topic you will be able to:
- state Newton's first, second and third laws precisely;
- use F = ma to link force, mass and acceleration;
- draw a free-body diagram and find the net force on a body;
- tell the difference between mass and weight;
- identify the two bodies in an action–reaction pair;
- solve simple numeric problems in newtons, kilograms and m/s2.