Hot air balloons have three main parts (see How a Hot Air Balloon Floats). The pilot and passengers ride in the basket. The colorful balloon that fills with air is called the envelope. Attached to the bottom of the envelope are burners powered by tanks of propane, a type of gas.
To take off, the pilot lights the burners, which produce a 12-foot flame. As the air inside the envelope warms, its molecules move faster and farther apart. Soon, the air becomes less dense than the air outside. The balloon lifts off! The upward force that allows the balloon to float is called buoyancy.
Making the flame larger causes the balloon to rise. It can soar as high as 3,000 feet! To travel back to the ground, the pilot opens a vent. This releases hot air through the balloon’s top.