What is Fluids?

A fluid is a substance that can flow when external force is applied on it. The term fluids include both liquids and gases. Though liquids and gases are termed as fluids, there are marked differences between them.

For example, gases are compressible whereas liquids are nearly in compressible. We only use those properties of liquids and gases, which are linked with their ability to flow, while discussing the mechanics of fluids.