Heat rises. Hot air rises. It goes up. When you see a bowl of hot soup, you can hold your hand above the bowl and feel the heat going up into the air. Heat rises.

Have you ever stood near a campfire and felt heat rising from the flames. Sometimes little pieces of ash float up into the air. The smoke also rises with the hot air. You can toast your marshmallow in the rising heat.

The air around us is made up of molecules. Tiny bits of oxygen, carbon, hydrogen, and other chemicals join together to form molecules. When the air is cold, the molecules move slowly and stay close together. The air is dense. When the air is hot, the molecules spread out and move around quickly. The air is less dense. It weighs less. When the air weighs less, it floats up. When you heat the air that is inside the balloon, it makes the balloon float up into the sky.

In the bottom of the basket of the balloon are two propane tanks. You might use propane in a gas stove if you go camping. There are hoses that run from the tanks to the burners above the basket. When the pilot wants to go up, he uses the burner to heat the air inside the balloon. Then the balloon goes up into the air and floats with the wind. The hot air makes the balloon go up. As the air cools, the balloon will come down. The wind direction controls which way the balloon goes, and how fast it moves.