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Pressure

Gases are made up of atoms and molecules, which are in constant and rapid motion. The atoms and molecules are constantly hitting the walls of the gas container. In doing so they exert pressure on the walls.

Gases have no definite shape or volume. The shape and volume of a gas depend on its container. Compared with solids and liquids, the molecules of a gas are relatively far apart. Hence they can be compressed, or forced into a smaller space. But if the volume of a gas is decreased, its pressure increases, because the molecules hit the walls more often and more rapidly.

The more a gas is compressed, the greater its resistance to compression. If a large amount of gas is forced into a small space, it becomes difficult to compress further. Under very high pressure, compressed gas can be used for transmitting power.

As gas pressure is increased, the molecules are forced closer together. If this continues, the molecules eventually become attached to one another. At this point, the gas changes into a liquid.

The pressure of a gas varies with temperature. Pressure is in direct proportion to absolute temperature, since the higher the temperature, the more rapid the motion of the molecules, and consequently the greater the pressure exerted on the walls of the container. Conversely, the higher the pressure of a gas, the higher its temperature. When a gas is compressed, it becomes hotter.

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