ABSTRACT
Engineers always seem to have definitions for just about anything and everything (most of which cannot be easily understood by many of us). An engineer might refer to air as a fluid, because it is. Like water, air is fluid and it can be poured. Engineers are primarily interested in air as a fluid because they deal with fluid mechanics, the study of the behavior of fluids (including air) at rest or in motion. Fluids may be either gases or liquids. You are probably familiar with the physical difference between gases and liquids, as exhibited by air and water, but for the study of fluid mechanics (and the purposes of this text) it is convenient to classify fluids according to their compressibility.
