Buoyant Force:
When a body is immersed party or wholly in a liquid, a force acts on the body
by the liquid in the upward direction. This force is called buoyant force or
force of buoyancy or up thrust. It is equal to the weight of liquid displaced
by the body and acts at the centre of gravity of displaced liquid. Its study
was first made by Archimedes.
Archimedes Principle:
when a body is immersed partly or wholly in a liquid, there is an apparent loss
in the weight of the body which is equal to the weight of liquid displaced by
the body.
Law of Floatation
A body floats in a
liquid if
(i)
Density of material of body is less than or
equal to the density of liquid.
(ii)
If density of material of body is equal to
density of liquid, the body floats fully submerged in liquid in neutral equilibrium.
(iii)
When body floats in neutral equilibrium, the
weight of the body is equal to the weight
of displaced liquid.
(iv)
The centre of gravity of the body and centre of
gravity of the displaced liquid should be in one vertical line.
Centre of Buoyancy: The centre of gravity of the liquid displaced
by body is called centre of buoyancy.
Meta centre: When
a floating body is slight tilted from equilibrium position, the centre of
buoyancy shifts. The point at which the vertical line passing through the new
position of centre of buoyancy meets with the initial line is called Meta
centre.
Conditions for stable
equilibrium of Floating body
(i)
The Meta centre must always be higher than the
centre gravity of the body.
(ii)
The line joining the centre of gravity of the
body and centre of flotation should be vertical.
Density: Density is defined as mass per unit volume.
Density = mass
/ volume. It s Si unit is kg/ m³.
Relative density = density of
material /
Density of
water at 4˚ C
Since relative density is ratio, it is unites.
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