Tried to figure it out in public and ended up looking like an absolute fool so imma need someone to explain this to me
In: Biology
When air moves fast out of the mouth, it sucks in ambient air, which is colder. To test this, blow (“hoo”) on the palm of your hand through a “tube” made of the other palm (make sure it’s tight), or a toilet paper tube.
It has nothing to do with “compression” or Bernoulli principle.
What you go “hoo” the air your pushing out of your lungs increases in pressure as it moves through the smaller opening in your lips and then quickly decreases in pressure after it’s left. This decrease in pressure reduces its temperature because the air particles are moving further away from each other, dissipating their energy into kinetic rather than thermal.
When you go “Haa” there is less of a pressure difference between your lip opening and the outside air than when you go “hoo” so the pressure change is lower so more thermal energy is kept in the air. Therefore, when you go “Haa” the temperature of the air is closer to the temperature in your lungs.
Its the same reason that you can feel your deoderant can getting cold when you hold the nozzle down for a while. The pressure in the can is decreasing as you let the gas out.
Edit: This affect is known as Gay-Lussac’s Law (aka The pressure temperature law)
[deleted]
When you do a “hoo”, the air is coming out from a very small opening which gives it a higher chance to mix with the air around it and cool down.
When you do a “haa”, the air is coming out at a larger volume and needs more time to cool down.
**Edit**
Put your finger right in front your mouth when doing a “hoo” and you will sense that it’s actually just as hot as a “haa”, but cools much faster a few cms away.
Latest Answers