why do we breathe out water vapour

Brrr! It's freezing this morning in Wonderopolis. We woke up to a thick
of on the grass. Be sure to up as you head to the bus stop. You don't want to get! As you wait for the and talk with your friends, you may notice that you can see your breath. If you and your friends all at the same time, you can make a big in the air. Did you and your friends suddenly turn into -breathing? Or is something else going on here? Why can you see your breath when it's cold outside but not when it's hot? Believe it or not, there's nothing magical about seeing your breath when it's cold outside. It's just science at work. You may already know that when you breathe in, your body takes in from the air. When you breathe out, your lungs expel carbon dioxide back into the air.


But the breath you breathe out contains more than just carbon dioxide. When you ( out), your breath also contains. Because your mouth and lungs are moist, each breath you contains a little bit of water in the form of water (the gas form of water). For water to stay a gas in the form of water, it needs enough energy to keep its molecules moving. Inside your lungs where it's nice and warm, this isn't a problem. When you and it's cold outside, though, the water in your breath loses its energy quickly. Rather than to move freely, the molecules begin to pack themselves closely together. As they do so, they slow down and begin to change into either liquid or solid forms of water. This process is called. When you when it's cold outside, the water in your breath condenses into lots of tiny droplets of liquid water and ice (solid water) that you can see in the air as a, similar to.


When it's warm out, though, the water gas stays, because the warm air provides energy that allows the water to remain a gas. As temperatures drop, it's more likely that you'll be able to see your breath. There's no exact at which will occur. Many factors other than can play a role in, including (the amount of in the air). When it falls below 45б F (7. 22б C), though, you can usually expect to be able to see your breath. The water molecules in (say) a glass of water or a pond have a lot of different energies, even though you d measure the bulk water as being at a certain temperature.


But that s just an average. Some of the molecules are moving fast enough to escape the liquid and head out into the air, but they re under the surface and just bang around off other nearby molecules. But some of them, up near the surface, actually do fly off. As this happens over time, we call it evaporation. Water molecules stick to each other pretty tightly (thus surface tension, among other things), but an individual molecule can pick up enough speed to break loose. When you heat up a body of water, you re increasing the average kinetic energy of the water molecules in it, so a greater fraction of them have the energy to break loose. The boiling point is the temperature at which the molecules have no choice but to do that: if they re at the surface, they re gone, and the time it takes the water to boil away is dependent on the surface area and how many can take flight at once.


Another way to look at this is to think about humidity. That s water vapor in the air, and we re used to feeling dry air and moist air. But just because the air is carrying a lot of water vapor in it doesn t mean that the air is at the temperature of boiling water. Those water molecules in the vapor phase have a distribution of energies, just like the ones in the liquid phase in a glass of water. If they slow down enough, they ll stick to any other water molecules they encounter, instead of bouncing off again, and that means that it s cool enough for dew or rain to form.

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