Have you ever wondered why some surfaces, such as glass or metal, sometimes fog up?

This is caused by condensation.

Condensation

When liquid water is heated, it turns into a gas called water vapour.

water vapour

When this vapour hits a cold surface, like this glass tube, it cools down.

It turns back, or condenses, into tiny drops of liquid water.

Condensation is the process of a gas changing state to become a liquid.

0°C

But what do you think happens if water is cooled down even further?

Its molecules lose energy and start to slow down.

Eventually they can no longer move freely and can only vibrate.

The molecules now form a fixed shape.

The water freezes into solid ice.

freezing
liquid changes to solid

The temperature at which a liquid freezes is known as its freezing point.

freezing point
temperature a liquid freezes at

Water has a freezing point of 0 degrees Celsius.

0°C

Different liquids have different freezing points.

Shampoo will freeze at minus 3 degrees Celsius.

–3°C

And perfume will still be liquid at temperatures below minus 80 degrees Celsius.

below –80°C

Petrol has a freezing point of around minus 60 degrees Celsius.

–60°C

That means it won't freeze in your car even if it's cold enough for water to freeze into snow.

condensation
freezing
freezing point