Question

Buoyant force exerted on an object immersed in a liquid arises due to

• A. Repulsion of molecules of the liquid
• B. Force exerted by the liquid on sides of the object
• C. Difference between pressures exerted by the liquid at top the and at the bottom of the object
• D. None of these

Answer 1

The correct option is C Difference between pressures exerted by the liquid at top the and at the bottom of the object

When a mug filled with water is immersed in a bucket containing water as shown in the figure given below, water exerts force on the sides of the mug as well as on its top and bottom (shown by arrows). The sideways force exerted by water on the mug being equal and opposite cancel out. The force of water acting on the top of the mug acts in downward direction and a force of water acting on the bottom of the mug acts in upward direction. As we know the pressure exerted by liquid in depth is greater than that on the surface of liquid. As the top A of the mug is at a lower depth in water, it experiences less downward force. The bottom B of the mug is at a greater depth in water, so it experiences greater force at B in upward direction. Thus, there is a net upward force on the mug. This net force acting on the mug in upward direction is called buoyant force which reduces the effective weight of the mug and it seems lighter.