| Is our air from our breath hot or cold? If the
air that comes out from our breath is hot then why
we try to blow the hot food to make it cooler?
But if it is cold, so why then when we feel cold
we start to blow our hands to get warmer?|
|Question Date: 2016-09-07|
The air that leaves our bodies is about 98
Fahrenheit, or 37 o Centigrade. If we’re
food that is hotter than that, our breath will
cool it. If we’re blowing on food that is colder
than that, our breath will warm it. Here’s a
question for you. Make a guess, then actually test
it. Put cups of hot and cold water in front of a
regular fan (not a heater or air conditioner).
Leave them there for a long time. Will the fan
keep making them colder or hotter, or just get
them to room temperature? You can have
controls by putting the same kind of cups with the
same amount of water in a place away from the fan.
Thanks for asking,
The temperature of our breath is the
temperature of our bodies. This is warmer than
most things, but cooler than really hot food.
Air from human lungs is a little below body
temperature. So if the food is hotter than
body temperature, blowing body temperature air on
it will cool it off. The blowing speed will has
have an effect. even warm air can capture some of
the heat from the food that is a little warmer
than the air and move on the air quickly will
allow the cooling to happen faster.
Since our breath is close to our body
temperature, this is why it is effective to warm
our hands with our breath.
Good question! Hot and cold are relative terms,
what temperatures are considered hot? Your
breath is pretty close to the same temperature as
your body, 98.6 Fahrenheit. So if the temperature
outside is a lot colder than 98 Fahrenheit, your
breath will feel much warmer. Although I don't
recommend blowing on your hands to warm them, it's
more efficient to create heat from friction by
rubbing your hands together. Cooling your food
with your breath is actually not related to the
temperature of your breath, but the fact that the
wind your breath creates changes the surface
tension of the water in the food you're blowing on
so that more water evaporates, and more heat is
lost in the process of changing liquid water into
steam, thus cooling liquid water and the food.
Our breath is hot, since it comes from our
lungs which are at body temperature (about
98°Fahrenheit). In fact, we lose water every
time we breathe out because our lungs make the
water humid because of the high temperature and
then we breathe out the wet water. Hot food is
still way hotter than human breath. Most hot food
is steaming and steam has a temperature of
212°Fahrenheit so the food could potentially be
100° hotter than your breath. Whenever there is
a temperature difference between two substances,
heat flows from the hotter object to the colder
object. In this case, even if our breath is
hot, it will be cold compared to the food we are
eating. But even if our breath was close to the
temperature of the food, it would still cool due
to “convective cooling.”
Convective cooling just means when air is
moving, it transfers heat faster than if it’s not
moving. That’s why a fan can make you feel cooler
even though the air is not cooler. As the air
passes by you, since it’s moving it transfers heat
away much faster than if the air is still. As
for breathing on your hands when they’re cold,
your breath will be significantly hotter than your
Let's assume that by saying "our breath" you
mean the air that comes out of our lungs and our
mouth or nose. Since it is in our body, it has the
temperature of our body 36.6 Centigrade. So, no
matter if it is cold outside or hot outside, the
air coming out of us has very very similar
That's why, if you go to a cold place (like
skiing in the mountain, or in New York in the
winter) your breath will be warmer than the
outside air and will be effective to warm your
hands for a little.
If your soup or hot chocolate is too hot, it
probably is at a temperature higher than 40
Centigrade. Therefore your breath will cool it.
However! That's not all! You can cool down your
soup just by waving the air above it. What happens
is that when your food is hot, the air aboves it
gets hot. That air *slowly* moves up and allows
cooler air to replace it above our food, so our
food will eventually get cooler. But if we blow,
then we remove that hot air above our food more
efficiently, so it gets replaced by cooler air
faster! Finally, as we blow our breath, the
faster we blow, the cooler our breath gets.
You can try that with a baloon. Blow it to fill it
and then hold it and let it deflate suddenly while
holding it. Feel how cool the outgoing air is
that you put inside as warm air?
What we feel as heat or cold is the
temperature difference between us and the object,
not the temperature itself. When you say
something feels hot or cold, you are comparing its
temperature to the air in the room (25°Centigrade)
or the temperature of your skin (34°Centigrade).
We feel energy flow from the hotter object into
the colder object until they reach the same
temperature. So, if an object is the same
temperature as your skin, it won’t feel hot or
cold. Thermal energy can flow in different ways:
- by conduction, where energy flows
directly between two objects that touch.
- by convection, where energy flows into
the air (or water) around an object, carrying the
energy toward or away from the object.
- or by radiation, where energy is released
as infrared light (so weak that we can’t see it).
Your breath is closer to your inner
body temperature of 34°Centigrade. Is it hotter
or colder than room temperature
(25°Centigrade)? You can warm your hands
by blowing on them because your breath is hotter
than your skin (particularly on a cold day). By
blowing, you transfer energy from inside your body
to your hands by convection. Moist air, like
your breath, carries a lot of energy so it warms
things more quickly than dry air.
When you blow on a hot drink like
tea or cocoa, you are using convection to cool -
your breath is 37°Centigrade and most drinks are
served between 70 and 85°Centigrade. But your
breath isn’t carrying much of the drink’s energy
away. Instead, your breath stirs the air around
your cup, blowing the hot air directly over the
liquid away so that cool air can replace it and
soak up more energy. You can cool the drink in the
same way by waving your hand over it, using the
wind or a fan – anything that moves the air over
the liquid surface. The faster you move the air,
the faster it will cool. Just be careful not to
Our breath starts out the same temperature as
our bodies. Then it changes to the temperature of
the air around us after it comes out of our
We blow on hot food to cool it because our
breath blows away some of the hot air rising off
the food. That kind of air movement is called
We can blow on our hands to warm them if our
hands are colder than the main parts of our
bodies. I don't think I've ever blown on my hands
to warm them, but sometimes I'll put them on my
cheeks or under my armpits to warm them.
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