Newton's Three Laws of Motion, Explained Simply
Almost all everyday motion — a kicked ball, a braking car, a rocket — is explained by Isaac Newton's three laws. Here is each one in plain language with an example.
First law: inertia
An object stays at rest, or keeps moving at a constant speed in a straight line, unless a force acts on it. A ball on the floor does not move until you kick it; a moving car keeps going until friction and brakes slow it.
Second law: F = ma
The force on an object equals its mass times its acceleration. Heavier objects need more force to speed up the same amount. Push a shopping cart that is empty vs. full with the same force — the full one accelerates less.
Third law: action and reaction
For every action there is an equal and opposite reaction. When you jump, your legs push down on the ground and the ground pushes you up. A rocket pushes gas down; the gas pushes the rocket up.
Frequently asked questions
What is inertia?
Inertia is an object's resistance to changes in its motion. More mass means more inertia.
What does F = ma mean?
Force equals mass times acceleration. It tells you how much an object speeds up when a force is applied — bigger mass, smaller acceleration for the same force.