Imagine putting a cloud on a scale
How much does a cloud weigh? It looks like the lightest thing in the whole world — soft, white, and fluffy, like cotton drifting past the window. You can almost see straight through its edges. So how could something that airy weigh anything at all?
Here is the strange part: that puffy white shape on a summer day is hiding a secret. It is not light at all. In fact, it is so heavy you may not believe it — and yet it hangs up there, perfectly calm.
What is a cloud actually made of?
A cloud is built from millions upon millions of tiny water droplets. Each droplet is smaller than a grain of sand — so small that a hundred in a row would barely fill the dot at the end of this sentence.
When the sun warms oceans, lakes, and wet grass, invisible water vapour rises into the sky. High up, where the air is colder, the vapour gathers into droplets around even tinier specks of dust. Billions of droplets together make a cloud.
And now the surprise: add up all the droplets in an ordinary summer cloud, and they weigh about 500 tonnes. That is roughly the weight of a hundred elephants, gathered high in the sky.
Did you know? A single cloud can weigh as much as a hundred elephants — and still it floats silently above your head.
Why doesn't the cloud fall on us?
If a cloud weighs a hundred elephants, why doesn't it drop straight down? The answer lies in how small the droplets are. When something is tiny, it falls incredibly slowly — think of a feather, or a speck of dust drifting in a sunbeam by the window.
Warm air also rises from the ground all the time, gently pushing the droplets upward, the way wind holds a kite aloft. The weight is spread across such a huge space that it never piles up in one spot. Only when many droplets squeeze together into big, heavy drops do they finally fall — and that is rain.
Try it at home: Weigh the invisible water
We can't weigh a whole cloud, but we can feel how heavy invisible water really is — with a sponge.
You'll need: a kitchen scale, a sponge or rolled-up cloth, a bowl of water.
- Weigh the dry sponge and write down the number.
- Soak the sponge until it is full.
- Lift it, squeeze gently so it doesn't drip.
- Weigh it again and subtract the first number — that is the hidden water!
What happens if you use a bigger sponge?
Questions to wonder about
- Where does all the water go when a cloud disappears from the sky?
- If a cloud is so heavy, why can't we feel its weight when a plane flies through it?
- Can a cloud become too heavy to hold all its water — and what happens then?
Every child is made of good atoms — and some of them look upward and wonder.