question_answer

When you whistle out air on to your palm held close to your mouth, the air feels cold; but when you blow out air from your mouth, keeping it wide open, the air feels hot. Why?

Answer:

                During whistling, we blow out air through a small opening between the lips. This is an adiabatic expansion, so there is a fall in temperature. But when we keep our mouth wide open, hot air of the mouth blows on to the palm which feels hot.