Fluid Mechanics (Part-3) (General Engineering) (SSC JE)

Surface tension is defined as the tensile force acting on the surface of a liquid in contact with a gas or on the surface between two immiscible liquids such that the contact surface behaves like a membrane under tension.

Surface tension–The energy required per unit area of the fluid to maintain its surface is called as surface tension due to this energy the fluid surface has tendency to shrink into the minimum surface area that is possible therefore the falling drops of water become sphere because it has minimum surface area as compare to other geometry.

The ratio between inertia force /viscous force is Reynolds's number.
• The ratio of the inertia force and the pressure force is called as the Euler number
• The ratio of the inertia force and the gravity force is called as the Froude's number
Reynold's number– The ratio of the inertia force to viscous force is called reynold's number.

Archimedes principle- When a body is wholly or partially submerged in a liquid , then the vertical upward force acting on the body known as buoyant force is equal to the weight of the liquid displaced by the immersed part of the body . Buoyant force = Net upward force = weight of liquid displaced.

Venturimeter is a rate of flow or discharge measurement device of the large diameter containing three section as.
(i) Convergent cone
(ii) Throat
(iii) Divergent cone
It is most accurate discharge measuring device based on Euler's equation.
Head loss in Venturimeter is so small.
Coefficient of Discharge 0.94 - 0.98
A venturimeter has a differential mercury water manometer connected to its inlet and throat for a given discharge in the pipe is independent of the orientation of venturimeter.

Spherical shape of droplets of mercury is due to high surface tension because it has very high cohesion between molecules of mercury.

Poise–It is the C.G.S unit of dynamic viscosity.

A substance in liquid or gaseous phase is referred to as fluid. They are capable of deforming continuously under the action of shear stress, however small the shear stress may be.
• It has no definite shape of its own, but conforms to the shape of the containing vessel.

Due to decreasing the temperature of water will be decrease the vapour pressure of water contained in a sealed tube.

The capillary depression in mercury is on account of cohesion being greater than the adhesion between molecules of mercury. If cohesion is less than adhesion then capillary rise takes place. e.g. H₂O