Toss a ball into the air and it always comes back down. Jump as high as you can, and the ground pulls you back. That downward pull is called gravity, and it comes from the Earth.

Gravity is an invisible force that pulls every object toward the center of the Earth. You cannot see it or hold it, but you feel it all the time. It is the reason things fall down instead of floating up.

The bigger and heavier an object is, the stronger its gravity pulls. The Earth is huge, so its gravity is strong enough to hold you, the oceans, and the whole sky of air right onto the ground.

Long ago a scientist named Isaac Newton wondered why an apple fell from a tree instead of drifting sideways. His big idea was that the same pull that drops an apple also keeps the Moon circling the Earth.

Gravity does not only pull light things. A feather and a heavy rock are both pulled down, but the feather floats slowly because the air pushes back on its wide, light shape. Drop them where there is no air and they fall together.

Gravity is at work every second of your life. It keeps your feet on the floor, makes rivers flow downhill, and lets you pour milk into a bowl instead of watching it float away.