Why the car widows getting steamy, when it is raining or freezing?
Cold air can contain less moisture than warm air. If there’s too much water vapour in the air then the excess has to be removed somehow – in terms of weather it falls as rain or forms dew on surfaces. Condensation is much the same thing. Because the car windows are cold it cools the air next to them to that point that the air has more water vapour than it can contain. The air then deposits excess water vapour as condensation on the car windows – same reason cold surfaces such as windows, mirrors, tiles etc steam up in kitchens and bathrooms. If the humidity is high then there’s already a lot of water vapour in the air so it doesn’t need much more water vapour to reach it’s maximum capacity (called saturation point). If the people in the car are wet from rain then there will be a lot of evapouration and the windows will steam up very quickly. Having the heater on warms the air and so it can contain more water vapour before causing condensation, having a window open removes the moisture
