What you do:
• Open your mouth wide and blow air into your palm. Observe.
• Then purse your lips and blow air into your palm. Observe.
What you find:
The air is warmer when you blow with your mouth wide open.
Why?
The temperature of the air coming out of the open mouth is more or less the same as that of the body, and hence it is warm. When you purse your lips, the air gets compressed and comes out in a thin stream but once, outside, it expands and cools. Another reason for the difference is that the fast moving stream of air draws in cool air from the surroundings.
Picture Credit : Google
