Buoyant Force | Class IX

When an object is immersed in a liquid, it experiences an upward force due to the liquid due to this is looses weight. This upward force is called Buoyant force. Buoyant force is also known as upthrust.
1. When a piece of cork is held below the surface of water and then released, the cork immediately rises to the surface. It means some upward force is exerted by water on the cork which pushes it to the surface.
2. When a stone lying at the bottom of a pond is lifted up, it appears to be light as long as it is being lifted inside water. But as soon as the stone is lifted out of water into air. one feels it to be much heavier. It means some upward force acts on the stone when it is immersed in water and makes us feel lighter.

Factors Affecting Buoyant Force
The magnitude of Buoyant force acting on an object immersed in a liquid depends on two factors:
(i) Volume of the Solid object immersed in the liquid:As the volume of object immersed inside the liquid increases. the upward buoyant force increases. When the object is completely immersed in the liquid, the buoyant force becomes maximum.

(ii) Density of the liquid in which the object is immersed:As the density of liquid increases. the buoyant force exerted by the liquid also increases.
e.g. sea-water has higher density than fresh water, therefore sea-water will exert more buoyant  force on an object immersed in it than the fresh water.