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Grade 11Thermal Physics

How can you best use a spoon to cool a cup of coffee? Stirring – which involves doing work – would seem to heat the coffee rather than cool it.

Simran Bhatia

11 Years agoGrade 11

1 Answer

Mihir

11 Years ago

Whenever we dip the spoon to stir the coffee, it is at a lower temperature than the coffee. Now, here the spoon acts as a cold reservoir so heat flows from coffee to spoon. Hence the temperature tends to lower down a bit.
Secondly, stirring doesn’t heat up the coffee. The concept involved here is convection. Here, while stirring, the heat currents rise up to the surface and cool due to the temperature difference between atmosphere and coffee. If you were to stir a cup of coffee in a room having temperature same as that of the coffee (though you yourself won’t survive!!), this phenomenon wouldn’t take place.

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