The atmosphere always has some water vapour. Clouds form when the atmosphere can no longer hold all the invisible air vapor. Any more water vapor condenses into very small water drops.
Warm air holds more water vapor than cool air. So if warm air with lots of water inside cools, it can form a cloud. These are ways air can cool enough to form clouds:
Clouds are heavy. The water in a cloud can have a mass of several million tons. Every cubic metre (m3) of the cloud has only about 5 grams of water in it. Cloud droplets are also about 1000 times heavier than evaporated water, so they are much heavier than air. They do not fall, but stay in the air, because there is warm air all round the heavier water droplets. When water changes from gas to droplets, this makes heat. Because the droplets are very small, they "stick" to the warm air.
Sometimes, clouds appear to be brilliant colors at sunrise or sunset. This is due to dust particles in the air.
Clouds are classified according to how they look and how high the base of the cloud is in the sky. This system was suggested in 1803. There are different sorts of clouds because the air where they form can be still or moving forward or up and down at different speeds. Very thick clouds with large enough water droplets can make rain or snow, and the biggest clouds can make thunder and lightning.
There are five basic families of clouds based on how they look:
The following is a summary of the main cloud types arranged by how high they form:
High clouds form from in cold places, in mild regions and in the very hot tropics. They are too high and thin to produce rain or snow.
High-level clouds include:
Middle clouds usually form at in colder areas. However, they may form as high as in the tropics where it's very warm all year. Middle clouds are usually made of water droplets but may also have some ice crystals. They occasionally produce rain or snow that usually evaporates before reaching the ground.
Medium-level clouds include:
Low-level clouds are usually seen from near ground level to as high as . Low clouds are usually made of water droplets and may occasionally produce very light rain, drizzle, or snow.
Low-level clouds include:
When very low stratus cloud touches the ground, it is called fog.
These are clouds of medium thickness that can form anywhere from near ground level to as high as . Medium-level cumulus does not have "alto" added to its name. The tops of these clouds are usually not much higher than . Vertical clouds often create rain and snow. They are made mostly of water droplets, but when they push up through cold higher levels they may also have ice crystals.
Moderate-vertical clouds include:
These clouds are very tall with tops usually higher than . They can create heavy rain and snow showers. Cumulonimbus, the biggest clouds of all, can also produce thunderstorms. These clouds are mostly made of water droplets, but the tops of very large cumulonimbus clouds are often made mostly of ice crystals.
Towering-vertical clouds include:
In the Bible, clouds are often a sign of God's presence.
Water cycle
The water cycle (or hydrological cycle) is the cycle that water goes through on Earth.
Water is essential for life as we know it. It is present throughout the Solar System, and was part of the Earth from its formation. The source of the water was the same as the source of the Earth's rock : the cloud particles which condensed in the origin of the solar system.
This is the process that water starts and ends in the water cycle.
Human activities that change the water cycle include:
Water vapor
Water vapor is water that is in the form of a vapor, or gas. It is a part of the water cycle. When liquid water is heated to boiling point, 100 degrees Celsius (212 F), it turns into vapor. Water vapor can also be produced directly from ice; this is called sublimation. Steam is water vapor, but clouds are liquid water. The amount of water vapor in air is called humidity and it affects weather conditions. In the cold, breathing out causes the water vapor in the breath to freeze.
Water vapor weighs less than air, thus slightly reduces the lift produced by an aircraft wing.
Water vapour is transparent. The small droplets that look white like mist are actually liquid.
Water vapour is a big cause of the greenhouse effect.
Water vapor is invisible but when it condenses it makes visible water.
Solid
Solid is one of the three common states of matter. The molecules in solids are closely bound together, they can only vibrate. This means solids have a definite shape that only changes when a force is applied. This is different to liquids and gases which move randomly, a process called flow.
When a solid becomes a liquid, this is called melting. Liquids become solid by freezing. Some solids, like dry ice, can turn into gas without turning liquid first. This is called sublimation.
The forces between the atoms in a solid can take many forms. For example, a crystal of sodium chloride (common salt) is made up of ionic sodium and chlorine, which are held together by ionic bonds. In diamond or silicon, the atoms share electrons and make covalent bonds. In metals, electrons are shared in metallic bonding. Some solids, like most organic compounds, are held together with "van der Waals forces" coming from the polarization of the electronic charge cloud on each molecule. The dissimilarities between the types of solid come from the differences between their bonding.
Most metals are strong, dense, and good conductors of electricity and heat. The mass of the elements in the periodic table, those to the left of a diagonal line drawn from boron to polonium, are metals. Mixtures of two or more elements in which the big component is a metal are known as alloys.
People have been using metals for many purposes since prehistoric times.
The strength and relialbility of metals has led to their widespread use in making of buildings and other things, as well as in most vehicles, many tools, pipes, road signs and railroad tracks. Iron and aluminium are the two most commonly used metals. They are also the most common metals in the Earth's crust. Iron is most commonly used in the form of an alloy, steel, which has up to 2.1% carbon, making it much harder than pure iron.
Since metals are good conductors of electricity, they are valuable in electrical tools and for carrying an electric current over long distances with little energy loss. Because of this, electrical power grids rely on metal cables to get electricity. Home electrical systems, for example, are wired with copper for its good conducting uses. The high thermal conductivity of most metals also makes them useful for stovetop cooking utensils.
Minerals are natural solids formed through many geological processes under high pressures. To be thought as a true mineral, a substance must have a crystal structure with uniform physical things throughout. Minerals differ in composition from pure elements and simple salts to very complex silicates with thousands of known forms. In contrast, a rock sample is a random aggregate of minerals and/or mineraloids, and has no specific chemical composition. Most of the rocks of the Earth's crust have quartz (crystalline SiO), feldspar, mica, chlorite, kaolin, calcite, epidote, olivine, augite, hornblende, magnetite, hematite, limonite and a few other minerals. Some minerals, like quartz, mica or feldspar are common, while others have been found in only a few places in the world. The largest group of minerals by far is the silicates (most rocks are ≥95% silicates), which are made largely of silicon and oxygen, also with ions of aluminium, magnesium, iron, calcium and other metals.
Evaporation
Evaporation is when a liquid becomes a gas without forming bubbles inside the liquid volume. If bubbles are formed we are talking instead about "boiling".