We normally see,whenever a body is placed over a Liquid,either it sinks or floats on the Liquid.
The body placed over the Liquid is subjected to the following two forces.
02)Upthrust of the Liquid.
These two forces acts opposite to each other.If the Gravitational Force is more than the Upthrust of the Liquid,the Body will sink down,if the Gravitational Force is less than the Upthrust of the Liquid,the Body will float.
This will best understood by the Archimede's Principle.
It states that "Whenever a body is immersed wholly or partially in a Fluid,it is lifted up by a force equal to a Weight of Fluid Displaced by the Body".
The tendency of a Fluid to uplift a submerged body,because of upward thrust of the Fluid,is known as Buoyancy.It is always equal to the Weight of Fluid Displaced by the Body.
If the Force of the Buoyancy is less than the Weight of the Body,it will sink down.When the Force of the Buoyancy is more than the Weight of the Body,it will pushed up till the Weight of the Fluid Displaced is equal to the Weight of the Body.
03)Centre Of Buoyancy:-
It is the point,through which the force of the Buoyancy is supposed to act.It is always the Centre of Gravity of the Volume of the Liquid Displaced.
Whenever a body,floating in a Liquid,is given a small angular Displacement,it starts Oscillating about some point.This point,about which Body starts Oscillating,is known as "Metacentre".
The distance between the centre of Gravity of a floating Body,and the Metacentre is called "Metacentric Height".More the Metacentric Height of floating Body,more it will be stable.