Why does blowing on food make it cooler

You change the situation when you blow on food. You move your relatively cooler breath where the heated air used to be convection. This increases the energy difference between the food and its surroundings and allows the food to cool more quickly than it would otherwise. When you blow on a hot drink or a food containing a lot of moisture, most of the cooling effect is due to evaporative cooling.

Evaporative cooling is so powerful, it can even lower the surface temperature below room temperature. Here's how it works. Water molecules in hot foods and drinks have enough energy to escape into the air, changing from liquid water to gaseous water water vapor. The phase change absorbs energy, so when it occurs, it lowers the energy of the remaining food, cooling it.

If you aren't convinced, you can feel the effect if you blow on rubbing alcohol on your skin. Eventually, a cloud of vapor surrounds the food, which limits the ability of other water molecules near the surface to vaporize. The limiting effect is mainly due to vapor pressure, which is the pressure the water vapor exerts back on the food, keeping water molecules from changing phase.

When you blow on the food, you push away the vapor cloud, lowering the vapor pressure and allowing more water to evaporate. Heat transfer and evaporation are increased when you blow on food, so you can use your breath to make hot foods cooler and cold foods warmer. The effect works best when there is a large temperature difference between your breath and the food or drink, so blowing on a spoonful of hot soup will be much more effective than trying to cool a cup of lukewarm water. Since evaporative cooling works best with liquids or moist foods, you can cool down hot cocoa by blowing on it better than you can cool a molten grilled cheese sandwich.

Another effective method of cooling your food is to increase its surface area. Chopping up hot food or spreading it out on the plate will help it lose heat more quickly. Actively scan device characteristics for identification. Use precise geolocation data.

Sure, most of the molecules inside will have a speed that's given by the average temperature, but there's going to be a range: many will be hotter and many will be colder.

What you don't see on the diagram above is that for any temperature, some of the molecules more for hotter temperatures, fewer for lower temperatures will be above the temperature threshold to enter the gaseous phase. If you've ever observed steam rising off your hot beverage, that's actually arising from the hottest, most energetic molecules inside entering the gaseous phase, condensing back into rising liquid droplets as the cool air above interacts with them.

Which is why, if you put your nose above a steaming cup of coffee, it comes out not just hot, but also wet!

When you blow into the hot liquid, yes, the air you're causing to come into contact with the liquid is cooler than the liquid itself, and so that heat exchange will help your beverage cool faster. But a big effect also comes from the fact that when you blow on your beverage, you're increasing the number and changing the sample of molecules in contact with the air, and so you increase the rate at which the hottest molecules evaporate, entering the gaseous phase and leaving your liquid.

The big reason this is important is when you allow the hottest molecules to escape, they take that heat with them , leaving you with an overall cooler system than you started with! The next time someone berates you for blowing too strongly on your hot beverage, you'll have science to back you up. A more vigorous blow helps the hottest molecules escape faster, leading you to enjoy your drink at the right temperature faster than anyone else!

This is a BETA experience. You may opt-out by clicking here. More From Forbes. Jul 23, , am EDT. Jul 15, , am EDT. I understand heat as being a function of the motion of molecules. Something that is hot has more energy. This is about all I know. We also blow on things to make them hot -- like your hands in the winter.

Aesop wrote a fable about this both the fable and scientific explanation are here Put your hand over don't touch! Sense the hot air there? Dipping something in cold water will cool it much quicker than dipping it in warm water, for example. That's why you put stuff on the refrigerator: the air there is colder, so things you put in there will cool quicker than stuff on the outside air unless you live in Canada : The thing is: the air around your hot food becomes hot.

So, it isn't really good in taking the heat off your food. Cold, humid, air absorbs heat quicker than the hot air. Also, most food contains water because we do and blowing air over the food increases the evaporation rate, which takes heat out of the food. But that's a smaller factor than simple convection. Den Beste at AM on March 30, Basically, heat is how fast a bunch of molecules are moving how much energy each one has. It is the sum. Temperature is the average of the heat energy of each molecule so it doesn't change with mass.

Applying heat ie, energy to a substance will make it raise in temperature according to its specific heat capacity. Specific heats are very, very important things to know for materials.