What physical states are covered under fluid mechanics?

Fluid mechanics is the branch of physics that studies the behavior of fluids, which include both liquids and gases, when they are at rest and in motion. The key characteristic of fluids is that they are substances that flow and can take the shape of their container.

Liquids and gases are both considered fluids because they share similar properties that govern their behavior, such as viscosity and density, although they have different states of matter. Liquids have a definite volume but take the shape of their container, while gases have neither a definite shape nor a definite volume, expanding to fill the entire space available.

Understanding fluid mechanics requires an examination of the principles governing the behavior of both states. These principles are crucial in various applications, including engineering, meteorology, and even biology, where the movement of fluids plays a significant role.

Therefore, the inclusion of both liquids and gases in the study of fluid mechanics makes this option the most comprehensive and accurate in representing what is covered within this field.