Why does “Hoo” produce cold air but “Haa” produces hot air ?


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 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.

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.

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)

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.

There’s two things to note here:


The human body doesn’t feel absolute temperature, what you feel is how much heat is entering (hot) or leaving (cold) your body (That’s why metals always feel a lot hotter or colder than their surrounding, high heat conductivity).

So in the case of your breath, the air comes out faster on the “Hoo” sound. A faster flow of air will carry more heat away from your hand via convection. As someone else pointed out, it is the same reason a fan cools you down even though the air doesn’t get any colder.


The reason the “Hoo” sound produces a faster airflow than the “Haa” sound for the same effort has to do with the opening size in your throat. If your lungs are pushing the same amount of air in both instances, the air will have to come out faster if the opening is smaller.

Think of a garden hose when partially block the opening with your thumb, the water comes out faster!

I disagree with the answers referring to drop in pressure (adiabatic effect), since the pressure difference just isn’t sufficient.

Instead, the answers around speed are more accurate. The body is pretty warm, and the more contact that the air gets with us, the warmer it gets. Even then, rapid air over the surfaces (like our mouths and throats) tends to cool them, so the slower the air is, the more chance the body can keep those surfaces warm with circulating blood.

Also, while “hoo” moves air faster, “haa” has greater turbidity around the vocal chords, which means that the air gets more stirred up and more of it gets in contact with the warm surfaces.

How many of you, (like myself) tested the temps for yourself after reading the headline?

The temperature should be close to the same, but fast moving air wicks away more heat than slow moving air.

The “hoo” motion involves pursing ones lips closer together so the air coming out moves faster because of the higher pressure inside the mouth.

The “haa” motion involves leaving ones mouth more open, the air coming out moves slower because of the low pressure inside the mouth.

If there was anything more to it, I think its possible that the temperature of the air is coming from the lungs, and when you say “haa”, that the total volume of air comes out more quickly and so does not have a chance to cool down.

When you say “hoo”, the total volume of air comes out more slowly, and probably cools down as it passes over your lips, which are much cooler than the core of your body

Well also compressing air through a small opening will cool the air, look up Pop bottle air conditioning