What is compressed air?

Compressed air is defined as air that has been squeezed into a smaller space, leading to an increase in pressure. This process involves reducing the volume of the air while maintaining its mass, resulting in a higher density of air molecules within a confined area. This increase in pressure is crucial for various applications, especially in air brake systems where it is used to activate and control the braking mechanism. The efficiency and effectiveness of air brakes rely heavily on this principle, as the pressurized air is essential for creating the necessary force to engage the brakes on vehicles.

In contrast, heated air can cause expansion rather than compression, and mixing air with hydraulic fluid or filtering air are unrelated to the fundamental concept of compressed air. This makes the correct choice pivotal in understanding the basic principles behind air brake systems and their operation.