Digital Dimdima
Blowing Out

If I hold my hand in front of my open mouth and blow, the air feels warm but if I blow through pursed lips the air is cooler. Why?

Air coming out of the open mouth is more or less at the temperature of the inside of the body, so it is warm.
When air is blown in a thin stream through the lips, it feels cooler because whenever a gas expands, it cools. When the air is forced through pursed lips, it is compressed slightly and when it is released from the mouth it expands and cools.
Another reason for its coldness is that the fast-moving stream of air draws in cold air from the surroundings.

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