Gravity is the invisible force that pulls every object with mass towards every other object with mass. It is the weakest of the four basic forces of nature, but it has unlimited reach and works on everything that has mass, so it shapes the entire universe. Gravity holds you on the ground, holds the Moon in orbit around Earth, holds the planets in orbit around the Sun, and holds the galaxies together. Without gravity, nothing in the universe would ever clump together. There would be no stars, no planets, no us.
- What it doesPulls masses togetherAlways attracts, never repels
- Earths surface pull9.8 m/s2Speeds up falling things
- Moons gravity1/6 of EarthsAstronauts bounce
- Sun gravity holds8 planets + many small bodiesAcross billions of km
- Causes tidesMainly the Moons pullSea rises and falls
- Extreme gravityBlack holesEven light cannot escape
What you will learn here
- What is gravity: the basic idea.
- Why dont we float away: how Earths gravity keeps us down.
- Gravity in space: orbits, moons and planets.
- Weightlessness: why astronauts float in orbit.
- The tides: how the Moon pulls the sea.
- Black holes and extreme gravity: where space itself is bent.
Why it matters
Without gravity, the Earth would fly off into space and so would you. The Sun would not exist (gas clouds need gravity to clump into stars). The Moon would not orbit. The tides would not happen. Engineers also have to fight gravity every day: every building, bridge and aeroplane is designed to handle Earths constant pull. Understanding gravity helps us launch satellites, predict eclipses, study galaxies and even imagine the start of the universe.