Ice is put into a tumbler containing water at room temperature. To cool water quickly, should the ice be allowed to float naturally in water or be pushed to the bottom of the tumbler with spoon and held there? Justify your answer.

Explanation

To cool water quickly, ice should be allowed to float naturally in water.
Justification:
When ice melts, water in the vicinity gets cooled and becomes denser. If ice is made to stay at the bottom of the tumbler, water at bottom becomes cold. But, colder water being denser remains at bottom. As a result, cooling occurs slowly. On the contrary, if ice is allowed to float naturally in the water i.e., at the surface, water at surface becomes cold. It becomes denser and goes down and warmer water from bottom being less dense rises up to replace it. This mixing causes water to cool quickly.