Learn more physics!
Its not cold out, its raining, our windows are open, and when we breathe out, we can see our breath, just like on a cold day. Whats happening?
- Jess (age 18)
It may not be cold out, but it's still probably colder out than inside
your body. Your breath is saturated with water vapor, meaning that if
there were any more water molecules in it they would start to condense
into droplets. If the breath cools down a little, that makes it easier
for water to stay in liquid drops rather than in separate molecules, so
visible drops start to form. On a dry day, it may be that by the time
the drops would have formed, so much water has diffused out into the
dry air that there's not enough left to form liquid. On a wet day,
almost as much diffuses in as out.
All these processes are governed by the laws of thermodynamics,
which determine whether the liquid is stable in the presence of some
concentration of gas molecules at some temeprature.
(republished on 07/24/06)
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