In general, we find in nature a balance between liquid and vapor (or gas). This means that both are present, and interact.

Here's how it thinks it necessary to design liquid water at the bottom, where the molecules are agitated, but they remain prisoners of the whole. Inevitably, from time to time, the molecules escape from the water. They are ejected by shocks. They become gas above the water. But the reverse can occur: the molecules of water vapor may be captured by the liquid. If there is enough steam above the liquid, there are as many gas captured by the liquid as liquid evaporates. There is a balance.

The degree of the air hydrometry measure whether we are close or not this balance. A 100%, equilibrium is reached, this means that the air is saturated with water: if you are taking liquid, it does not evaporate. It will be in equilibrium with the vapor in the air. Below 100%, which is still the rule in our latitudes, the liquid left alone evaporate naturally. That is why the machine can dry. This is not the case in hot countries, where the air is often saturated steam. The machine then dry it very badly, not at all vore.

To vaporize the water, it must allow water molecules to escape the pull of their neighbors. Therefore in the snatch, ie providing of energy. This means that when water molecules escape the liquid, they take with it a share of the energy of the liquid: the liquid cools, actually! This is very useful, yes!

The best example is the sweat if you sue, which means that our skin gets wet when it was hot, because it is evaporating, water takes the heat us from . It cools us. When it is hot, that's why the fans are refreshing: it is not that they make the air colder, it's just that they lead to air dry to our skin, and thus facilitate the evaporation of sweat. It's like when there is when we stop the warmest. While running, it's the dry air, which is evaporate your sweat. Stopping, the air in contact with your skin renews itself does less well, it is saturated with water, so you suez, but as the evaporation is not effective, you are hot.

When we say that time is "heavy" is in fact the air is saturated with water, or almost. In this case, the sweat evaporates much less. It also no longer plays its role. It was hot much faster than in dry air. And if the air is saturated with water, rain is likely ...