A brick suspended from a spring balance is lowered, gradually, into water. The reading of spring balance decreases, gradually, till it has a certain constant value. Explain the reason.

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Solution

When the brick is immersed in water, an upward buoyant force or the upthrust acts on the body.
The upthrust depends upon the volume of the body immersed or the volume of water displaced.
As more and more volume of the body is immersed, the upthrust acting on the brick will also increase gradually.
This gradual increase in upthrust causes a gradual decrease in the apparent weight shown by the spring balance.
The increase in upthrust will be there till the point the brick is fully immersed in the water. After which the spring balance will show a constant value.

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