In a gas, the molecules are far apart and in constant motion. They bounce off each other with no loss of energy.
A gas always fills up the container it is in, because the molecules will get farther and farther apart from each other in order to fill the available space.
However, the number of molecules in a gas does not change as it fills up the container it is in. The amount of pressure that the gas exerts is related to how many molecules of gas are in the container. The more molecules, the higher the pressure.
Assume you are filling a basketball or a bicycle tire with air. If you double the amount of air inside, you are doubling the number of molecules while the available volume remains the same. The ball or tire will feel harder on the outside as you double the pressure. This is one way to change pressure; you are increasing the pressure of the gas by adding more gas to the container.
Another way to increase the pressure of a gas is to decrease the size of the container and keep the same amount of gas molecules inside. If we reduce the size of the container by half and the amount of gas (the number of molecules) inside is unchanged, the amount of pressure exerted on the walls of the container will double.
Air Pressure
What is one way to change the pressure of a gas?
One way to change the pressure of a gas is to decrease the size of the container or add molecules of gas to the container.
