Characteristics of Fluids

The study of rigid bodies is limited to solids, as liquids and gases do not have a definite shape and conform to the available space around them. Because of this, they are collectively called fluids.

Forces applied tangentially to a surface are called shearing forces. Solids resist shearing forces, but fluids deform continuously when a shearing force is applied.

In solids, the molecules are close together, and the strong forces between the molecules make them incompressible.

Fluids have large intermolecular distances and weak intermolecular forces that allow the molecules to move freely.

Among fluids, liquids have a definite volume and are incompressible. However, the separation between molecules is much larger in gases. For this reason, gases do not have a definite volume and are highly compressible.

Fluid mechanics is the study of the behavior of fluids, which can broadly be classified under two branches. Fluid statics is the study of the properties of fluids at rest, and fluid dynamics deals with the study of fluids in motion.