Hot Air Balloon

How do hot air balloons work?

The science behind hot air balloon flight is the same science that makes you float in a pool. It's DENSITY! If you are less dense than water, you float; if you are more dense, you sink. Density is calculated by taking the mass of an object and dividing it by the volume of the object. Air has mass and volume. We usually talk about the volume of air in cubic feet or meters. 

So, if there is air inside a hot air balloon and air outside of the balloon, how can they have different densities? It all has to do with temperature. Temperature is a measure of the average kinetic energy (energy of motion) of the atoms in a substance. The warmer a substance gets, the faster its atoms move, and the higher the temperature is! When we heat the atoms inside of the hot air balloon they move much faster than the atoms on the outside. This means there can be fewer atoms inside the balloon and still have the same air pressure as the surrounding air. This means the balloon is less dense and it floats.

For more information about balloons, check out the link below. To build your own hot air balloon click on the directions below.

http://www.howstuffworks.com/transport/flight/modern/hot-air-balloon.htm