Air is all around us, but because it is difficult to see it is often hard to understand. You have probably heard that hot air rises and cool air falls. You may have even noticed that the air is warmer on the top floor of a two story building. However, have you ever wondered about the reason that hot air rises? Keep reading to find the answer.
What causes hot air to rise?
Firstly, it is important to know that the air all around us consists of molecules that are constantly in motion (moving). When the air begins to heat these molecules start to move faster and bump into each other. This causes more space between the molecules and the air expands to become lighter (less dense). This causes the hot air to rise. Once this hot air begins to cool it begins to move more slowly and becomes heavier again (more dense) and it slowly sinks back to the ground. This principle is used to keep hot air balloons in the air (and to bring them down again).
There are a number of experiments to demonstrate the fact that hot air rises. One of my favorites is the teabag rocket experiment. The following video demonstrates how to do this. Remember that you should ask an adult to help you to do this!