Jump as high as you can. Go on, try it. No matter how hard you jump, you always come back down. You never float away. You never drift up toward the ceiling. Something always pulls you back. That something has a name, and it is one of the most important forces in the entire universe. It is called gravity, and without it, nothing about life on Earth, or anywhere else in the universe, would work the way it does.
Gravity is an invisible pulling force. You cannot see it, touch it, or smell it, but you feel it every single second of every day. It is the reason your pencil falls when you drop it. It is the reason rain falls downward. It is the reason you can pour water into a glass instead of watching it float away. Gravity is the Earth pulling everything toward its centre, and it does this with everything, all the time, without ever stopping.
The story of how we figured this out is one of the best in science. In the 1660s, a scientist named Isaac Newton was sitting near an apple tree when he saw an apple fall to the ground. Most people would have just picked it up and eaten it. But Newton asked a question that nobody had properly asked before: why did it fall down? Why not sideways? Why not upward? He realised that something must be pulling the apple toward the Earth. He called that pulling force gravity. Then he asked an even bigger question: if the Earth can pull on an apple, can it also pull on the Moon? The answer turned out to be yes, and that one curious thought changed science forever.
Newton worked out that every single object in the universe pulls on every other object. A big rock pulls on a small rock. The Moon pulls on the Earth. The Earth pulls on the Moon. Even you pull on everything around you, though you are not heavy enough for anyone to notice! The heavier something is, the stronger its pull. Earth is enormously heavy, which is why its gravity is strong enough to hold you firmly on the ground and keep the atmosphere in place so you have air to breathe.
Here is something that surprises a lot of people: there is gravity in space too. It does not just disappear once you leave Earth. Astronauts on the International Space Station are actually still being pulled by Earth's gravity. They float not because there is no gravity, but because the space station is constantly falling around the Earth at exactly the right speed, like a ball thrown so fast and so far that it keeps missing the ground. That floating feeling is actually falling, just sideways, forever.
Gravity also explains why you would feel much lighter on the Moon. The Moon is smaller and less heavy than Earth, so its gravity is about six times weaker. If you weigh 30 kilograms on Earth, you would weigh only about 5 kilograms on the Moon. You could jump much higher, and things would fall much more slowly. On a planet bigger than Earth, like Jupiter, you would feel so heavy you probably could not even lift your arms.
The same gravity that makes your mango fall off the tree is the same force holding the Moon in orbit around Earth, holding Earth in orbit around the Sun, and holding the Sun inside the Milky Way. One force, working across the entire universe, holding everything in its place. It started with a falling apple and a scientist who refused to stop asking why.