Q: Why can there be frost on a car on a night when the air temperature stays above 32?F or 0?C?

A: The short answer is that objects can radiatively transfer heat to the very cold night sky on a clear night.
The longer answer includes consideration of conductive and convective heat transfer from other materials in contact with the water, and energy changes associated with condensation/evaporation and freezing/thawing.

You may find Dr. David Kilty’s discussion of radiative heat transfer, “How to Freeze to Death in Wyoming in the Summertime,”  informative and entertaining. 

Tags: Black Body, Freezing, Radiative Heat Transfer

Q: Why can there be frost on a car on a night when the air temperature stays above 32?F or 0?C?

A: The short answer is that objects can radiatively transfer heat to the very cold night sky on a clear night.

The longer answer includes consideration of conductive and convective heat transfer from other materials in contact with the water, and energy changes associated with condensation/evaporation and freezing/thawing.

You may find Dr. David Kilty’s discussion of radiative heat transfer, “How to Freeze to Death in Wyoming in the Summertime,” informative and entertaining. 

Tags: Black Body, Freezing, Radiative Heat Transfer

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