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# TNPSC Free Notes Physics In English – Properties of Fluids

இந்தக் கட்டுரையில், TNPSC குரூப் 1, குரூப் 2, குரூப் 2A, குரூப் 4 மாநிலப் போட்டித் தேர்வுகளான TNUSRB, TRB, TET, TNEB போன்றவற்றுக்கான  முறைகள் இலவசக் குறிப்புகளைப் பெறுவீர்கள்.தேர்வுக்கு தயாராவோர் இங்குள்ள பாடக்குறிப்புகளை படித்து பயன்பெற வாழ்த்துகிறோம்.

### Properties of Fluids

Density:
 It is the ratio of mass of the liquid by its volume.It is denoted by ρ.The S.I unit density is
Kg/m 3
 ρ = m / v
Pressure:
 It is the product Density ,Acceleration due to gravity and Pressure head
 P = ρgh
 1 atm = 1.013 x 10 5 Pa or N m -2
Pascal law:
If the pressure in a liquid is changed at a particular point, the change is transmitted to the entire
liquid without being diminished in magnitude.

Application – Hydraulic lift
Relative density or Specific gravity:
It is ratio of the density of a substance to the density of water at 4 ºC.
Buoyancy:
Up thrust or buoyant force is a force exerted by a liquid when a body falls in it

Law of Floatation:
The weight of the liquid displaced by the immersed part of the body equals the weight of the
body.
Properties of fluids:
Viscosity:
The property of a fluid to oppose the relative motion between its layers.Its unit is Ns/m 2 .
Co-efficient of viscosity:
 F ∝ A and F ∝ dv/dx
 F = -ƞ A (dv/dx)
 η is called the coefficient of viscosity of the liquid
 F is viscous force
 A is area of the liquid
 dv/dx is velocity gradient
Applications of viscosity:
 The oil used as a lubricant for heavy machinery parts should have a high viscous
coefficient.
 The highly viscous liquid is used to damp the motion of some instruments and is used as
brake oil in hydraulic brakes.
 Blood circulation through arteries and veins depends upon the viscosity of fluids
 Millikan conducted the oil drop experiment to determine the charge of an electron. He
used the knowledge of viscosity to determine the charge.

Reynolds number:
 It is used to find the type of flow of a liquid.
 R c = (ρvD) / η
 R c = Reynolds number
 ρ = Density of the Liquid
 η = coefficient of viscosity
 v = Velocity of the liquid
 D = Diameter of the tube

Surface Tension:
The Property of a liquid to act as membrane in its surface due to cohesive force, J m -2 or N m -1
Examples for surface tension:
Water bugs and water striders walk on the surface of water.

The hairs of the painting brush cling together when taken out of water. This is because the water
films formed on them tends to contract to a minimum area.

Factors affecting the surface tension of a liquid:
 The presence of any contamination or impurities
 The presence of dissolved substances
 Electrification
 Temperature
Capillarity:
The rise or fall of a liquid in a narrow tube is called capillarity or capillary action. Depending on
the diameter of the capillary tube, liquid rises or falls to different heights

Bernoulli’s Theorem:
The sum of pressure energy, kinetic energy, and potential energy per unit mass of an
incompressible, non-viscous fluid in a streamlined flow remains a constant.

Applications of Bernoulli’s Theorem:
Blowing off roofs during wind storm:

P/ρ + (1/2) v 2 + gh = constant

Aerofoil lift:

Bunsen burner:

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