Newton's Laws in Everyday Life

Newton's laws explain why objects start, stop and change direction.

First Law — Inertia

An object stays at rest, or keeps moving at constant speed in a straight line, unless a resultant force acts on it. This tendency is inertia. A bus passenger lurches forward when the bus brakes because their body keeps moving.

Second Law — F = ma

The acceleration of an object is directly proportional to the resultant force and inversely proportional to its mass: force = mass × acceleration. The same push accelerates an empty trolley faster than a full one.

Third Law — Action and Reaction

For every action there is an equal and opposite reaction. When you push a wall, the wall pushes back on you. A rocket pushes gas downwards; the gas pushes the rocket upwards.

Practice

1. Why do passengers wear seatbelts? Relate your answer to inertia.
2. A force of 20 N acts on a 5 kg mass. Find the acceleration.
3. Give one example of Newton's third law from sport.

Recap

Newton's laws describe inertia, F = ma, and action-reaction pairs. They explain motion all around us.