Newton's Laws of Motion

Before we start

Who was Isaac Newton?

Over 300 years ago, a scientist named Isaac Newton figured out three simple rules that describe how objects move and how forces push and pull on them. We still use them today to build cars, bridges, roller coasters, and the rockets that fly to the Moon.

A force is just a push or a pull. Kicking a ball, gravity pulling you down, a magnet tugging on metal — those are all forces. Newton's laws tell us what forces do to the stuff they act on.

Newton's First Law

The Law of Inertia

"An object stays still, or keeps moving in a straight line at the same speed, unless a force acts on it."

Everything is a little bit lazy — it wants to keep doing whatever it's already doing. This "laziness" is called inertia. A resting object won't suddenly zoom off on its own, and a moving object won't speed up, slow down, or turn unless something pushes it.

On Earth a rolling ball stops — but only because friction and air are secretly pushing back on it. Remove those forces, like in space, and it would roll forever.

Newton's Second Law

Force, Mass & Acceleration

"The bigger the force, the faster something speeds up — but the heavier it is, the harder it is to move."

This law is famous as an equation:

That means Force = mass × acceleration. Flip it around and you get a = F ÷ m: acceleration is how fast the speed changes. Push the same cart harder and it accelerates more. Load it with bricks (more mass) and the same push barely moves it.

Newton's Third Law

Action & Reaction

"For every action, there is an equal and opposite reaction."

Forces always come in pairs. When you push on something, it pushes back on you just as hard, in the opposite direction. Jump off a skateboard and it rolls backward. This is exactly how a rocket flies: it throws hot gas downward, and the gas pushes the rocket upward.