Or how any fast moving object also provides cold air
In: Other
There are two reasons for this.
^
The first thing to understand is that most of the time, your skin is hotter than the surrounding air, because the chemical processes in your body are always heating it up. Thus when you blow air on yourself, you accelerate the speed of heat transfers from your skin to the air (through convection), and thus you feel a “cold” breeze.
Indeed, what you feel is heat leaving your body, not the true air temperature, so if moving hot air makes your body cool down as fast as colder still air, your subjective perception of both will be the same.
^
But what about when the air is actually hotter than your skin? When you get past the 30°C and get to the 40°C? Well, here comes the second – and more important – thing to understand : your most efficient way to cool your body down is not pure convection, but the evaporation of good old sweat.
To transform from a liquid to a gas, water needs a lot of energy, energy that it will then keep with itself on its merry gaseous way. Thus when your sweat evaporates, it will suck up a lot of heat from its surroundings – including your body – thus lowering your skin temperature and cooling you. And when you swat air on yourself, you accelerate the evaporation speed, thus you cool down faster, thus you feel like the air itself was cold.
This is the same reason a hot day in a humid country feels much hotter than in a dry country (something that can be measured using for example the [heat index](https://en.wikipedia.org/wiki/Heat_index)), as evaporation works faster when the air is dryer. This is also the main reason why throwing water on regular fires will extinguish them. There’s a few more things I would like to add, but for the sake of brevity, I’ll stop : however don’t hesitate to ask any further questions.
Latest Answers