Here's how it works:
* Gases are made of molecules that move freely. They have a lot of space between them and are constantly moving around.
* When you cool down a gas, the molecules slow down. They have less energy and start to move closer together.
* If you cool the gas enough, the molecules will get close enough that they start to attract each other. This attraction holds the molecules together, and the gas becomes a liquid.
It doesn't *have* to become a liquid, though. If you continue cooling the gas even further, it can become a solid. This is called freezing.
Here are some examples of gas turning into liquid:
* Water vapor in the air condensing into water droplets on a cold glass.
* Propane gas in a tank turning into liquid propane.
* The formation of clouds when water vapor in the air condenses.
The temperature at which a gas turns into a liquid is called its boiling point. This temperature is different for every type of gas.
