Question

Will a lake freeze faster on a windy day than a calm day?

Asked by: Ken Morgan

Answer

Evaporative cooling could cause the overall temperature of a lake to cool faster on a windy day than on a still one of the same temperature.

Any liquid has a thin layer of vapor over its surface, including water. This layer of gas is made up of a transient population of molecules with enough kinetic energy to separate from the rest of the molecules in the liquid and enter the gas phase. At any given temperature, the molecules in this layer will reach an equilibrium pressure, with a higher pressure for higher temperatures due to the higher average energy of the particles.

A windy day can pull can strip away some of the molecules in this vapor layer, thereby reducing the overall average energy of all particles. This is because the particles in the layer is made up of the molecules with a higher average energy than those in the liquid state, and so removing them lowers the overall average. Thus wind will speed energy loss from the lake. This is essentially the same reason you will feel cooler on a breezy day compared to a still one.

Answered by: Rob Landolfi, Science Teacher, Washington, DC

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