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LESSON NOTES

Buoyancy & Buoyant Force
Force applied by the fluid on a solid which is partially or fully submerged in liquid, is
called the buoyant force and this phenomenon is named as buoyancy.
Buoyant force acts in upward direction and it depends on the density of the fluid.
Factors affecting the Buoyant Force
Magnitude of the buoyant force depends on two factors:

1. Volume of the object immersed in liquid
2. Density of the liquid.
3. Acceleration due to gravity.
Buoyant force is directly proportional to volume of the object and density of the liquid.

Formula of Buoyant force
Fb = ρ x g x V
Where,

 Fb is the buoyant force
 ρ is the density the fluid

 V is the submerged volume
 g is the acceleration due to gravity
Why does an object sink or float over water?
When an object is immersed in water, it exerts pressure over water due to its weight. At
the same time water also exerts upward thrust, i.e., buoyant force over the object.

 If the force exerted by the object is greater than the buoyant force of water, the
object sinks in water.
 If the force exerted by the object is less than the buoyant force of water, the
object floats over water.

Archimedes Principle
When we go swimming, we feel a little weightless in the water. The reason for this is
that liquids exert an upward force to objects submerged in them. This is known as thrust
and is a consequence of the difference in pressure a liquid exerts at different heights.
As we submerge an object (considering it is fully submerged) deeper into a liquid, the
pressure exerted by the liquid keeps on increasing but the thrust force remains the
same.

What is Archimedes Principle?

It states that when a body is immersed fully or partially in a fluid, it experiences an
upward force that is equal to the weight of the fluid displaced by it.