Gravity is a force that pulls things toward each other. You pull on Earth with the same force that Earth pulls on you. Earth's gravity keeps you on the ground, and it makes things fall. It is why things fall when you drop them or throw them. A dropped thing falls faster and faster.

Anything that has mass also has gravity. Things with more mass have more gravity. Gravity gets weaker with distance, so the closer two things are, the stronger their pull.

Galileo showed how things fall when you leave out the air. Then heavy things and light things speed up at the same rate as they fall. A falling apple is said to have inspired Isaac Newton. He linked it to how the Moon moves. Gravity keeps the Moon moving around Earth. His theory of gravity came out in 1687.

The Moon's gravity pulls on the sea. It helps make ocean tides. The Moon's pull is the main cause of them. The Sun's gravity keeps Earth moving around the Sun. Planets travel around the Sun on oval paths. Those paths are called ellipses.

Words to know

• gravity: a pulling force
• mass: amount of stuff
• ellipses: oval paths
• tides: sea rising, falling