In this exhibit, the principle behind a hot air balloon is illustrated.
Hot air balloons are the oldest successful human flight technology, dating back to 1783. Today’s hot air balloons use heaters or burners fueled by propane, a liquified gas stored in pressure vessels, similar to high-pressure forklift cylinders. The amount of lift (or buoyancy) provided by a hot air balloon depends primarily upon the difference between the temperature of the air inside the balloon and the temperature of the air outside the balloon. When raising the air temperature inside the balloon, the volume expands and the balloon is made lighter than the surrounding (ambient) air. As a result the balloon and its payload is forced into the air.
Observe how the balloon begins to surge upwards at a certain temperature.