# Buoyancy and Archimedes' Principle

A mug filled with water appears to be heavier when it is lifted from bottom of the bucket to above the surface of water than the mug within the water in the bucket.

The upward force exerted by the water is known as the force of buoyancy or buoyant force. This force is also known as upthrust. All bodies experience a buoyant force when they are immersed in a fluid that is a liquid or a gas.

### Archimedes' Principle

Archimedes discovered a principle to determine the magnitude of the force of buoyancy. Archimedes' principle is stated as follows:

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.

From Archimedes' principle, the magnitude of the buoyant force acting on a body at a given place depends on

• density of the fluid
• volume of the body immersed in the fluid

Archimedes' principle has many applications. It is used in designing ships and submarines. Hydrometers which are used to determine the density of liquids are based on Archimedes' principle. Lactometers, which are used for determining the purity of milk, are also based on this principle.