Air flow is the movement of air from one area to another. It is the result of pressure differences between two areas. Air flow can be either natural or forced. Natural air flow occurs when air is pushed or pulled by differences in air pressure. For example, when air is heated, it rises and is replaced by cooler air. Forced air flow is created by mechanical means, such as fans or blowers. Forced air flow is used to move air through heating, ventilation, and air conditioning (HVAC) systems. Air flow is measured in terms of velocity, which is the speed of the air, and volume, which is the amount of air moved. The direction of air flow is also important, as it can affect the efficiency of HVAC systems. Air flow is an important factor in many industries, from aeronautics to industrial processes. Understanding air flow is essential for creating efficient and safe environments.