State Archimedes principle.

Explanation

Archimedes principle is the consequence of Pascal.s law. It states that a body immersed in a fluid experiences a vertical upward buoyant force equal to the weight of the liquid it displaces.
When a body is partially or completely immersed in a fluid at rest, it experiences an upthrust which is equal to the weight of the fluid displaced by it. Due to the upthrust acting on the body, it apparently loses a part of its weight and the apparent loss of weight is equal to upthrust.
Thus for a body either partially or completely immersed in a fluid,
upthrust = weight of the fluid displaced
= apparent loss of body weight
Apparent weight of an object = True weight of an object in air-upthrust (weight of water displaced)
Devices based on Archimedes principle are-hydrometers, lactometers, balloons, boats and ships, submarines, etc.