Why hot air comes out when we breathe and somtimes cold air comes out?
Answers
Earl Zwicker, a retired physicist who taught at the Illinois Institute of Technology, conducted informal experiments with fellow scientists to solve the mystery. Their conclusion: It's all about evaporation.
Blow through pursed lips, and your jet of streaming breath -- a bit of dry room air "entrained" along the way -- loses some of its own moisture. As with a blowing fan, the rushing air lowers the humidity at the surface of the skin. The result: Moisture evaporates like sweat on a dry day, and the skin feels cooler.But yawn out a breath, and the warm, moist air from our lungs emerges in a kind of cloud, with little mixing-in of dry room air. Humidity near the skin's surface rises. Evaporation from the skin temporarily decreases, and heat loss drops. And our skin feels warmer, like on a steamy day.