Why do things fall down?
A first look at gravity: the invisible pull of the Earth, and a drop race you can do in class.
Read
Drop a ball. Down it goes! It never falls up, and it never floats away. Something pulls it down. That pull is called gravity.[1]
Gravity is an invisible pull. The Earth pulls everything towards its middle: you, your shoes, the rain and the apples on a tree. That is why you always come back down when you jump.[1]
Big things pull harder. The Earth is very, very big, so its pull is strong. The Moon is much smaller, so its pull is about six times weaker. On the Moon you could jump much higher![1][2]
What falls faster, a hammer or a feather? On Earth the feather floats down slowly, because the air pushes against it. The Moon has no air. In 1971 the astronaut David Scott dropped a hammer and a feather on the Moon, and they landed at the same time![3]
Gravity also keeps the Moon going round and round the Earth.[1]
Try it: The drop race
You need
- A hard-cover book
- A sheet of paper, smaller than the book
- A soft place to land (a rug or a cushion)
Safety
Drop onto a soft surface and keep feet out of the way. Grown-ups hold anything heavy.
What to do
- Hold the book in one hand and the flat sheet of paper in the other, at the same height.
- Guess: which one lands first? Then let go of both at the same moment.
- Now crumple the paper into a ball. Drop the book and the paper ball together. What happens now?
- Put the flat paper on top of the book. Drop them together. Does the paper stay on the book?
What happens, and why?
The Earth pulls on the book and the paper. The flat paper is slow because the air pushes up against it, like a little parachute. When you crumple it, less air can push on it, so it falls faster. On top of the book, the book pushes the air out of the way, so the paper falls with the book.[3][6]
Play: Drop race
Two things are dropped together. Guess which one lands first, or tap 'Same time'. Watch out: is there air or not?
Your best score is kept only on this device. Nothing is sent anywhere.
Quiz
Other ages: Ages 10–11 · Ages 15–16