Charles' Law Lesson for Kids

Instructor: Erin Noxon
Did you know that gases, like oxygen, nitrogen, helium, and others, are made of atoms and are matter, too? Well they are, and there are laws that can help us understand how these gases behave. This lesson is going to go over one of the laws, named Charles' Law.

Charles' Law

You know how we have laws... like traffic laws. Well gases have laws too! One particular law we are going to look at today is Charles' Law.

Charles' Law was named for scientist Jacques Charles, who came up with the idea for the law around 1780. The law says that when temperature increases, the volume of a gas increases, and it increases at the same rate. What this means is, as a gas gets hotter, and its atoms move faster, the amount of space it takes up, or its volume, gets bigger, too.


In the animated image, notice that as the flame heats the yellow gas in the chamber, the atoms that make it up spread out and the gas expands, gets bigger, filling up more space. When the flame goes away, the atoms in the gas slow down and come back together, the gases volume gets smaller and smaller.

Helium Balloon

One easy example of Charles' Law is a helium balloon. If you fill a helium balloon in a warm or hot room, and then take it into a cold room, it shrinks up and looks like it has lost some of the air inside. But if you take it back to a warm or hot place, it fills back up and seems to be full again.

Basically, the helium inside spreads out and takes up more space, or volume, when it is warmer. This is because atoms move faster when they are warmer. When it cools down, it contracts, or pulls in, and takes up less space, and the atoms slow down.

Mylar Balloons Deflating

Car Tires

Another example is car tires. It is important to fill the tires with air to keep the air pressure inside the tires at a good level to keep the car driving well. However, you should always measure the tire pressure before you drive the car, when the car is cooled down. Why?

Flat tire on pavement

The reason relates to Charles' Law. As you drive around during the day, the tires get hot from all of the friction rubbing against the road. The air inside the car tires expands, so the volume of air in the tire increases. Because the tire isn't completely sealed, this can affect the pressure as well. This can change the measurement of how much air pressure is in the tire. So you should always measure the pressure when the tires are cold, and fill them to the right pressure then.

Try It Yourself

If you want to do your own experiment with Charles' Law, do this simple experiment at home.

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