OVER VIEW OF HYDRO STATICS - Thrust and Pressure -Density and specific gravity- Principle of Archimedes - Laws of Flotation

HYDRO STATICS

Hydrostatics is one of the branches of physics which deals with the properties of fluids at rest. The term fluids is generally applied to both liquids and gases.

Thrust and Pressure

          Thrust is a force exerted by a liquid on any surface with which it is in contact. In a liquid at rest, this thrust is normal to the surface. If the thrust is the same at all points on the surface it is said to be uniform.

Pressure    =   Thrust/Area

The pressure at a point increases as the depth of the point below the free surface of the liquid is increased. It depends on the depth of the point and the density of the liquid. Hence the pressure at all points in the same horizontal level in a liquid at rest are the same.

Density and specific gravity

The density of a substance is its mass per unit volume.

Density = mass/volume

The specific gravity or relative density of a substance is the ratio of the mass of the substance to the mass of an equal volume of water.

Specific gravity = Density of substance/Density of water

Principle of Archimedes

         

        When a body is immersed fully or partially in a liquid at rest, It experiences a resultant upward thrust equal to the weight of the liquid displaced by it.

Since the resultant thrust is in the upward direction it opposes the weight of the body. So the weight of a body immersed in a liquid at rest will appear to be less than its weight in air. The principle of Archimedes can also be stated thus.

          When a body is immersed in a liquid at rest it experiences an apparent loss of weight equal to the weight of the liquid displaced by it.

Properties of fluids

  ü  The free surface of a liquid at rest is horizontal.

  ü  The pressure is the same at all points in the same horizontal level in a liquid.

  

  ü  The pressure at any point inside a liquid at rest is the same in all directions.

  ü A liquid always tends to flow from a point of higher pressure to one of lower pressure.

  ü  The increase of pressure at any point in a liquid is equally transmitted to all the points in all the directions in the liquid. This is called Pascal’s law.

LAWS OF FLOTATION 

 o  The weight of the floating body is equal to the weight of the liquid displaced by it.

 o  The centre of gravity of the floating body and the centre of gravity of the liquid displaced are in the same vertical line.

Surface tension

Surface tension is defined as the force acting normally on the unit length of a line imagined on the surface of a liquid.

Viscosity

The internal friction in a liquid that opposes the relative motion between its different layers is called viscosity.

Barometer

A barometer is an instrument used to measure the atmospheric pressure.

Manometer

A manometer is a simple instrument used for measuring the pressure of a gas or liquid contained in a vessel. There are different types of manometers, depending on the pressure to be measured.