Write short notes on:

(1) Applications of Archimedes’ principle.

(2) Buoyant force.

<sub>(1) Applications of Archimedes’ principle:

(i) It is used to find the purity of gold.</sub>

Suppose we have a gold crown and we need to determine its purity. We also have a block of pure gold as a reference. The block and the crown have the same mass (as shown in the figure). Using Archimedes’ principle, we can compare the densities of the crown and the block. If the crown is less dense than the block, it will displace more water - owing to its greater volume. Consequently, the crown will experience a greater buoyant force than the block (as shown in the figure). This will indicate that the gold used in making the crown is not pure, but has some other metal or alloy mixed in it.

(ii) This principle is used in the working of ships, a lactometer and a hydrometer. A ship floats on the water very easily due to its design. Also a lactometer is used to find the purity of milk, and a hydrometer is used to find the density of liquid in early time.

₍₂₎Buoyant force:

The upward force exerted by a liquid on an object immersed in it is called a buoyant force. When you try to immerse an object in water, you can feel an upward force exerted on the object, which increases as you push the object deeper into the water.

If the density of an object is more than the density of the liquid, then it sinks in the liquid. This is because the buoyant force acting on the object is less than the force of gravity. On the other hand, if the density of the object is less than the density of the liquid, then it floats on the surface of the liquid. This is because the buoyant force acting on the object is greater than the force of gravity.