Question

Define ‘buoyant force’. What is the cause of buoyant force? Explain an activity to show how buoyant force changes as the volume of an object immersed in water changes.

Answer 1

Buoyant force:

1. When an object is immersed in water or any other fluid, we observe that the object experiences a force from the downward direction opposite to the gravitational pull, which is responsible for the decrease in its weight.
2. It is an upward force opposite to gravitational pull.

Cause of buoyant force:

1. This upward force exerted by the fluid opposes the weight of an object immersed in a fluid. As we know, the pressure in a fluid column increases with depth. Thus, the pressure at the bottom of an object submerged in the fluid is greater than that at the top.
2. The difference in this pressure results in a net upward force on the object which we define as buoyancy.

Hence, buoyant force act upward on an object submerged in water.

Activity to show how buoyant force changes as the volume of an object immersed in water changes:

1. Take a nail made of iron and place it on the water surface it will sink.
2. Take a small boat of iron of the same weight as that of an iron nail and place it on the water, it will float.
3. Buoyant force increases as the volume increases or when volume increases then the weight of a volume of water displaced by the body also increases. Thus, the buoyant force increases with volume.

Hence, the buoyant force is an upward force that is responsible for the loss in weight of the body.