Compressed air gets cold due to the process of adiabatic expansion. Adiabatic expansion occurs when a gas expands without exchanging heat with its surroundings.

When a gas is compressed, the molecules are forced closer together, resulting in an increase in the temperature of the gas. This is due to the increase in kinetic energy of the molecules as they collide more frequently with each other and the walls of the container.

However, when the compressed gas is then allowed to expand, the molecules spread out and the temperature of the gas decreases. This is because the molecules lose kinetic energy as they move farther apart, resulting in a decrease in temperature.

This process of adiabatic expansion is what causes compressed air to get cold. The expansion of the gas results in a drop in temperature, making the air feel colder when it is released from the compressor.

The amount of cooling that occurs during adiabatic expansion depends on the initial temperature and pressure of the gas, as well as the final temperature and pressure. The greater the difference between the initial and final conditions, the more cooling that will occur.

Compressed air is often used as a refrigerant in air conditioning systems, where it is used to cool the air in a building or vehicle. The compressed air is allowed to expand through a nozzle, which causes it to cool and absorb heat from the surrounding air. The cooled air is then circulated through the building or vehicle to provide a comfortable environment.

In summary, compressed air gets cold due to the process of adiabatic expansion, which occurs when a gas expands and loses kinetic energy, resulting in a decrease in temperature. This process is used in air conditioning systems to cool the air in a building or vehicle.