Gravity is the invisible force that pulls objects toward each other. Right now, gravity is pulling you toward the Earth, which is why you stay firmly on the ground instead of floating away into space. Drop a ball and gravity pulls it down. Jump in the air and gravity brings you back.

Every object with mass creates gravity, but you only notice it with really massive objects like planets, moons, and stars. Earth's gravity is strong enough to hold the atmosphere around us, keep the oceans in place, and make water flow downhill. The Moon's gravity is weaker because it's smaller, which is why astronauts can bounce around up there in giant leaps.

Gravity also reaches across vast distances of space. The Sun's gravity keeps Earth and all the other planets orbiting around it, like an invisible rope swinging us in a huge circle. Without gravity, the universe would be chaos: planets would drift away from their stars, stars wouldn't clump together into galaxies, and you'd float helplessly through your classroom.

Scientists still study gravity because it's stranger than it seems. Isaac Newton described how gravity affects all objects the same way, which is why a bowling ball and a feather fall at the same speed in a vacuum. Later, Albert Einstein showed that gravity actually bends space itself, like a heavy ball pressing down on a stretched rubber sheet.