The amount of water vapor in the air may change.Heat speeds up evaporation.Places that are hot and wet have more water vapor in the air.

WATER IN THE AIR

Water does not always evaporate at the same speed.Heat may make water evaporate faster.Wet clothes usually dry faster on warm,sunny days.How fast would the clothes dry on cool,cloudy days?

All air has some water vapor.Moist air has a lot o water vapor.Dry air can take up more water vapor.Dry air can take up more water vapor than moist air.Water evaporates faster in dry air.

Both of the places on the right are hot.

Water evaporates only where it meets the air.Suppose you are at a lake.The lake is six meters deep.Moving air speeds up evaporation too.Wet hair and clothes dry faster on windy days are even better for drying clothes.

CONDENSATION

Water vapor may condense to liquid  water  when it cools.The change is called condensation.Dew is a form of condensation.Dew may form on objects when the air cools at night.Water vapor may also change to a s solid.This is a special change that may happen when t he air is cooler than 0 degree C.The water vapor changes to frost.Frost is ice crystals that form from water vapor.

CLOUDS

Clouds also form when water vapor condenses.The water condenses on very small pieces of matter,like dust,in the air.In the cold air,the water vapor changes to small ice crystals.Clouds are made from millions of these drops or crystals.Clouds get bigger as more waterdrops or ice crystals form.

A cloud very close to the ground is called fog.

PRECIPITATION

Both the waterdrops or ice crystals in clouds are very small.They are so small they hang in the air.Sometimes the drops or cystals grow too large.When they grow large enough,they are too heavy to stay in the air.The drops or crystals fall to the ground.Water that falls from clouds is called precipitation.

Rain and snow are two kinds of precipitation.Rain is liquid water that falls when the air is warmer the 0 degree C .Snow is made of ice crystals that fall when the air is colder than 0 degree C.

Sleet and hail are two other kinds of precipitation.Sleet is frozen rain.Some hail is formed from many layers of ice.