Tell Me Why I Can See My Breath When It's Cold
Kai (left), age 4:
Because oxygen is in your mouth and you blow it out when it's cold. It's white and it comes out of your mouth and some people like to do that. In the summer, the oxygen is still in your mouth and it's sleeping, so you don't see it.
The Parent's Answer
Andre, Kai's mom: You have warm air inside you and cold air outside. When they mix, you get a white cloud.
The Scientist's Answer
Water has three phases: liquid, gas, and solid. Water vapor is the gas phase, and ice is the solid phase. What you are seeing when you see your breath, says Dennis Feltgen, a meteorologist at the NOAA National Weather Service in Silver Spring, Maryland, are little droplets of water condensing out of a gas that's in your lungs. Our breath contains a lot of vapor because our lungs are quite moist. When we head outside on a cold day, water molecules (the vapor) in our breath lose the energy that, when they're warm, keeps them moving. Instead of bouncing around, they crowd up next to each other. And as they slow down, the molecules change from a gas state to denser liquid and solid states — the visible cloud of tiny particles of water and ice that you see when you exhale.
How to Explain It to Kids
Go outside and have your kids blow on their hands so they can feel how warm their breath is compared to winter air. When our warm breath puffs into cold air, tiny droplets are squeezed out of it like water from a sponge. The drops make a small, vanishing cloud.
After huffing and puffing out in the cold, head back in to warm up with hot chocolate. The plume of steam from the boiling kettle is like your breath: hot and wet. As the jet of water-laden warm air mixes with the cooler air of the kitchen, moisture in it comes out as a cloud of water droplets. The droplets are so small, they disappear from view before ever reaching the ground — just like your frozen breath.