MECHANICAL PROPERTIES OF FLUIDS

Introduction
Fluid is that which can flow. Liquids and gases are fluids. A fluid has no definite shape. It assumes the shape of container. Fluid can not withstand tangential stress or shearing stress on its surface. That is why they flow. The shearing stress of fluids is about one millionth of solids. The compressibility of solids and liquids are much lower when compared with gases.
The main differences between the liquids and gases
1)Liquid is incompressible, while a gas is compressible
2)Liquid has  a free surface, while a gas has no free surface
Common properties of liquids and gases
1) Liquids and gases can flow and 2) Liquids and gases can exert pressure on walls of container
Thrust and pressure
The force acting perpendicular to surface is called thrust. The trust per unit area is called pressure.
BUOYANCY
Consider a body immersed in a liquid. The thrust acting on bottom surface will be greater than thrust on top side. Thrust in upper surface is downwards and thrust on bottom surface is upwards. Hnce body experiences a resultant upward thrust. The resultant upward thrust is called buoyant force or force of buoyancy. Because of this up thrust the body experiences a loss of weight. The buoyancy acts through the CG of displaced liquid. The center of gravity of displaced liquid is called the centre of buoyancy 

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