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Mechanical Properties of Fluids

Question

A balloon filled with gas is made to just float on the surface of water. What will happen to it if it is submerged a certain distance below the surface and released?

Answer

The weight of the balloon is just balanced by upward thrust on the surface. When it is pushed inside, due to additional pressure of water column, the gas in the balloon gets compressed as a result of which the upward thrust decreases. Now the weight of the balloon is greater than the upward thrust and the balloon will sink as the equilibrium is disturbed.