When we stir a liquid vigorously, it becomes warm. Is it a reversible process?

No, it is not a reversible process.

Explanation


1. When we stir a liquid vigorously, it becomes warm because we do work on the liquid and it increases its temperature.


2. To make it a reversible process, would require it to bring the temperature to its initial value by stirring the liquid in opposite direction. Only then we can call it a reversible process.


3. But we know that this is not possible. The only way we can decrease the temperature is by extracting heat from the liquid and not by stirring it in opposite direction.


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