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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
Answer 1:

The air that leaves our bodies is about 98 o Fahrenheit, or 37 o Centigrade. If we’re blowing on 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,

Answer 2:

The temperature of our breath is the temperature of our bodies. This is warmer than most things, but cooler than really hot food.

Answer 3:

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.

Answer 4:

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.

Answer 5:

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 cold hands.

Answer 6:

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 temperature.

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?

Answer 7:

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 spill! :P

Answer 8:

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 mouth.

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 convection.

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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