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.
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science