Science
What is gravity?
Quick answer
Gravity is the force that pulls objects towards each other. Earth's gravity pulls everything towards its centre, which is why things fall down and why the Moon orbits Earth.
In one sentence
Gravity is the invisible pulling force between objects, and Earth's gravity is what keeps your feet on the ground and makes dropped things fall.
Explained
Drop a ball and it falls. Throw it up and it comes back. That is gravity, a non-contact force that pulls objects towards each other.
Everything that has mass has gravity, even you and a pencil. But the pull is only strong when something is huge, like a planet or a star. Earth is so massive that its gravity pulls everything towards its centre. That is why people in Australia, Nigeria and Canada all feel "down" as towards the ground, even though they are on different sides of the planet.
Gravity also holds space together. The Sun's gravity keeps the planets moving in their orbits around it. Earth's gravity keeps the Moon circling us. Think of swinging a ball on a string around your head: the string pulls it inwards and keeps it going round. Gravity is like an invisible string.
The pull of gravity on you is your weight, measured in newtons. Your mass, the amount of stuff you are made of, stays the same everywhere. On the Moon, where gravity is about one sixth as strong, you would weigh much less, but your mass would be the same.
Isaac Newton described gravity mathematically in the 1680s. The famous story says a falling apple got him thinking, but there is no evidence it ever hit him on the head.
Examples
- A ball rolling down a slide.
- Rain falling from clouds.
- Ocean tides, caused mostly by the Moon's gravity pulling on Earth's water.
- A skydiver falling until the parachute opens and air resistance slows them.
Common mistakes
- "Heavier things fall faster." Without air, a hammer and a feather fall together. On Earth, air resistance slows light, spread-out things like feathers.
- "There is no gravity in space." Gravity reaches far into space. Astronauts float because they are in free fall around Earth.
- "Mass and weight are the same." Mass is how much stuff; weight is the pull of gravity on it.
Quick quiz
Gravity
Check what you know with 4 quick questions.
Question 1 of 4
Which way does Earth's gravity pull?
Practise it
Try it
Drop a crumpled ball of paper and a flat sheet at the same time, then two balls of different weight. Which land together? Then try more physics activities.
Gravity and forces activities
For grown-ups
Related topics
Forces
A force is a push or a pull. Forces can make things start moving, speed up, slow down, change direction or change shape. They are measured in newtons.
The Moon
The Moon is Earth's natural satellite, a rocky ball about a quarter of Earth's width that orbits us roughly once a month. It shines by reflecting sunlight.
The solar system
The solar system is the Sun and everything that orbits it, including eight planets, their moons, dwarf planets such as Pluto, asteroids and comets.
Mass and weight
Mass is how much stuff is in an object, measured in grams and kilograms. Weight is the pull of gravity on that mass. In everyday life people say weight for both.
Friction
Friction is a force that acts when two surfaces rub or slide against each other. It slows things down and turns movement into heat, and it also stops us slipping.
Electric circuits
An electric circuit is a complete loop that electricity flows around. A simple circuit has a battery, wires and a component like a bulb. If the loop is broken, the electricity stops.