Why if I blow air on my hand I can get it to be either hot or cold, depending on how open my mouth is?

Question

For instance, if I open my mouth as wide as the dentist tells me to and blow, it's hot. But if I keep my mouth pursed, as if I were going to whistle, it's cool air that I feel on my hand.

Answer 1

I think it just comes out faster while your mouth is nearly closed and it causes the heat flow away making it seem cooler. I would think the air should always be warm and at the same temperature having been inside your body.

Answer 2

I'll answer in reverse order:

1. When you purse your lips you are able to force the air out at greater pressure. Think of a garden hose where you can reduce the size of the nozzle. This increases the pressure at which the water comes out.

This air flowing at higher pressure evaporates sweat on your hand, making you feel cool. Same principle as a fan blowing air against your skin.

2. In contrast, opening your mouth wide does not permit you to force the air out at higher speed. Since the low-speed air is now no longer capable of evaporating sweat, you experience it at near body temperature.

Answer 3

Great question! There are two things going on here, and whichever one is dominant will control what your hand feels. One is the fact that your breath is at internal body temperature, but the skin of your hand is cooler than that, so if enough of your breath stays close enough to your hand soon after your breath leaves your body, your hand feels that warmth. A more open mouth means your breath is moving more slowly, so it stays close enough to your hand long enough for you to feel the warmth. If you close your mouth and blow quickly, the other process dominates. Your skin has moisture on it which gets colder as it evaporates (this is a major reason for the existence of sweat). With your mouth more closed, you get less breath moving over the skin of your hand more quickly, and the evaporation dominates the warming effect.

Answer 4

in case you park it very on the factor of your place or on a driveway then you certainly can use a much less costly 2kW fan heater on the top of a mains extension lead. you may get warmers for greater or less £15 from supermarkets and a suited extension lead isn't costly. Run the lead from a handy socket interior the domicile (with the aid of your letterbox if the plug will in good shape) and out to the motor vehicle. bypass the extension lead with the aid of a automobile window (partly open). sit down it on the back window shelf or front passenger seat. confirm that the air vent slots interior the fan heater are thoroughly unobstructed. Set it to no greater advantageous than 0.5 potential (it relatively is important for protection) and activate. Then bypass and have your breakfast. After frequently 20-25 minutes the motor vehicle would be thoroughly defrosted and the interior would be very pleasantly heat. this technique would not contain working the chilly engine at a quickly idle, that's undesirable for the engine, generates nasty fumes and likewise wastes extensive quantities of petrol. The mains electrical energy is plenty greater low priced than working a automobile engine and you in addition to mght get a heat cabin too.

Answer 5

Have'nt the slightest,but it schweet though hey. Lol