Define fluid mechanics.

Fluid mechanics is the branch of physics that studies fluids (liquids, gases, and plasmas) and the forces on them. It deals with fluid flow and the forces that act on them.

Units.

• Density ($\rho$): It is defined as the mass per unit volume of a fluid.

Its S.I. unit is $\text{kg/m}^3$.

• Viscosity ($\mu$): It is a measure of a fluid's resistance to flow. It describes the internal friction of a moving fluid. Its S.I. unit is $\text{Pa} \cdot \text{s}$ (Pascal-second) or $\text{N} \cdot \text{s/m}^2$.

• Specific Weight ($\gamma$): It is defined as the weight per unit volume of a fluid. It is also the product of density and acceleration due to gravity ($\gamma = \rho g$).

Its S.I. unit is $\text{N/m}^3$.