➥ **Defination of Fluid Mechanics:**

Fluid Mechanics is that Branch of science which deals with the behaviour of the fluids (liquid or gases) at rest as well as in motion. Thus this branch of science deals with the static, kinematics and dynamic aspects of fluids.

**Density or Mass Density:**– it is defined as the ratio of the mass of a fluid to its volume. Thus mass per unit volume of a fluid is called density. It is denoted by ρ (rho). SI unit is kg/m^{3}. The density of liquids may be considered as constant while that of gases changes changes with the variation of pressure and temperature.**Specific Weight or Weight Density:**– it is the ratio between the weight of a fluis to its volume. Thus weight per unit volume of a fluid is called weight density.**Specific Volume:**– it is defined as the volume of a fluid occupied by a unit mass or volume per unit mass of a fluid. It is expressed as m^{3}/kg.

**"Scientists dream about doing great things. Engineers do them."**