Examples... Put a glass in the freezer and a few minutes later take it out, it will frost over.
Going from air conditioned temperature inside to a hot summer day outside makes your glasses fog up.
Why?
Posted Aug 2, 2011, 8:39 PM UTC
What's important here isn't that the cold object is warming up, it's that the air around it is warmer and humid. When you heat water, the water molecules become more and more energetic, and they shake around more and more. When they reach the boiling point, the water starts to turn into a gas. When you introduce a cold object, it rapidly cools the water vapour directly around it, and turns it back into liquid. As this happens to more and more molecules directly around the cold object, they clump together, or condensate, and form tiny droplets. As these droplets form all over the object, it appears to fog up.
This principle is used in dehumidifiers to dry the air in rooms.
edit: i should note before people attack me - the reason that the cold object cools is because as the humidity conensates around it, what is happening is that the warm water molecules in the air are losing the energy that makes them warm to the cold object, and the cold object acquires heat. In fact, all of the molecules in the air are experiencing this transfer of energy with the object, but water is the only type of molecule that can turn back into a liquid at room temperature. All of the other components of air need to lose a looot more energy before losing their gas state.
Air always has moisture as a rule, among other elements and compounds. When you travel from cold to warm, the moisture in the air that was near your glasses condensed and since water is naturally adhesive to other objects because of its polar nature (magnetic at subatomic level) it sticks to your glasses as a "fog."