Fami
Rainbow rain clouds
A foam cloud on a glass of water fills up with colouring until it rains colour.
Materials
- 1Tall glassor A glass jar
- 200 mlWater
- 1 canShaving foamor Squirty cream (safe to touch)
- 2 coloursRed and blue food colouringor Watered-down poster paint
- 1Dinner plate
Step by step
- 1
Pour 200 ml of water into the tall glass
A little over half: that's the sky
- 2
Put a cloud of shaving foam on top
Let it poke out over the rim
- 3
Add 10 drops of red to the cloud
At first the foam holds it all
- 4
Then 10 drops of blue next to it
Wait a minute and watch under the cloud
Result
It's raining colour!
Why does it happen?
The foam is like a cloud: it keeps the colouring in its bubbles. When it can't hold any more, the coloured water, which is heavier than clear water, drips out underneath and sinks in coloured threads. Real clouds do the same: they gather tiny drops of water until they are too heavy, and it rains.
For parents
The science, so you can answer
A cloud holds water until it can't hold any more; then it rains. The foam does the same with the colouring.
Shaving foam is air trapped in soap bubbles. The coloured water first stays between those bubbles, like in a sponge. When the foam is saturated (it can't hold any more), the coloured water seeps out underneath. Because coloured water is slightly heavier than clear water, it sinks in threads before mixing; in the end the colour spreads through the whole glass by itself (diffusion). Real clouds are made of tiny floating droplets of water; when they bump into each other and join, the drops grow until they are too heavy and fall: that is rain.
What they will ask you
«Why doesn't the colour fall straight away?»
The foam keeps it between its bubbles, like a sponge. Only when it is full does it start to drip.
«Why does it fall in threads?»
Coloured water is a tiny bit heavier than clear water, so it sinks in little streams before it mixes.
«What are real clouds made of?»
Millions of water droplets (or tiny ice crystals) so small they float in the air. Not smoke, not cotton wool.
«Why are some clouds grey?»
Because they are packed with water and sunlight hardly gets through. They are usually the ones about to rain.
In real life: Look at the sky on a stormy day: clouds darken as they fill with water just before it rains. And if the water ends up purple, that is the red and blue mixing by themselves.
Animated step by step
Follow it with your phone on the table: it pauses at the end of each step.