Isaac Newton was a tiny man in real life. But he was a giant in the world of science.

Newton created the theory of gravity around 1665 or 1666. He came up with the idea that every physical object, whether it’s a person, an apple or a planet, exerts a force on other physical objects. A force is a push or pull in a certain direction. The bigger the body, the stronger the force. There are different types of forces, but this one is called gravitational.

Some say that Newton came up with his ideas about gravity after watching an apple fall. He wondered why the apple fell straight down. Why didn’t it fall sideways, or even up toward the sky?

Gravity does not just make apples fall from trees. It also holds us on the ground. Newton showed that gravity even makes the moon circle around Earth, and Earth around the sun, Martin Rees says. He was president of Britain’s Royal Society. The Royal Society is the United Kingdom’s national academy of science.

Newton Changes Science Forever

The theory of gravity was just one of Newton’s discoveries. He also loved calculus. This is a mathematical subject that studies rates. A rate is the measurement of how much something changes. Newton’s ideas in calculus are still used today.

Newton also studied optics, the science of light. He found out that white light is not just white. It is actually a mix of all the colors of the rainbow. Newton used his knowledge of light to make better telescopes.

Following his apple idea, Newton wrote three laws of motion. These laws changed all of science, and are still used by scientists today.

First Law of Motion: Inertia

An object that sits still will remain still unless a force is applied to it. An object that is moving will keep moving along a straight line unless an outside force is applied to it.

Second Law of Motion: Acceleration

An object will accelerate if force is applied to it.

Acceleration is the change of an object’s speed. The acceleration will happen in the same direction as the force.

This idea can also be written as force equals mass times acceleration, or F = ma.

Third Law of Motion: Action and Reaction

For every action there is always an equal and opposite reaction.