Editing Water

[[Category: Physics|Biology]]
== Explanation ==
Water is a chemical compound essential for [[life]] on [[Earth]]. It is made up of two [[atom]]s of [[hydrogen]] and [[oxygen]] and chemically written as '''H<sub>2</sub>O'''. When water is heated to its [[boiling point]] 100 °C, it [[boiling|boils]] and turns into [[gas]] called as [[water vapour]] and [[steam]]. When heat is removed from the water, and the temperature is brought down to its [[freezing point]] of 0 °C, it [[crystallization|crystallizes]] to form [[ice]]. On Earth, water occurs in all these three [[phase of matter|phases]] naturally. Water changes through this phases on earth through [[water cycle]]. Besides Earth, water is present universally.

== Frequently Asked Questions ==
=== Where did Earth's water come from? ===
It is speculated that the vast amount of water on Earth could have come from the [[meteorite]]s from the [[meteoroid]] impacts that happened a long time ago. When Earth formed, the temperature was hot enough that liquid water couldn't exist. So the best hypotheses postulate that the origins of water could be the regions of low temperature within the [[solar system]]. Based on observations and reasoning, the possible candidates are [[comet]]s, [[asteroid]]s, and meteorites. In the present, by analysing the water sample from oceans, we could easily determine the concentration of hydrogen isotopes in the water, which is primarily protium. Oceans on Earth also have [[chondrite]]s, a type of [[stony meteorite]] which broke away and crashed onto Earth from the early asteroids during its formation. The deuterium to hydrogen (protium) ratio of our water matches closely to the ratio of the same in these chondrites than that of any other comets or other [[trans-Neptunian object]]s that are rich in deuterium concentration. Therefore, it is plausible that the Earth's water should have originated from the early asteroids and should have crashed into the Earth as chondrites.

=== Where did the water in the universe come from? ===
The most abundant elements in the universe are hydrogen and helium. So to begin with, the universe never had water in the first place. Oxygen is needed to form water. This oxygen is produced in the universe inside stars, when they start to fuse helium to form heavier elements up to [[iron]]. Beyond the formation of iron, stars collapse due to its own [[gravity]] and massive stars explode violently as [[supernova]]. It is only at this time hydrogen and oxygen atoms bond together to form different phases of water molecules based on the temperature and pressure around them. If the temperature is low, they would form ice and get trapped inside small bodies like asteroids. And when they enter a planetary body like Earth, they would exist as liquid water, further maintained by the planet's water cycle.

=== How does the water cycle work? ===
Water cycle works with the help of the [[Sun]] heating up the water in the [[ocean]]s. As water [[evaporation|evaporates]] into water vapour, the warm gaseous phase of water rises above. The temperature of water vapour drop with [[altitude]] and thereby lose energy. They expand and cool in the atmosphere. Due to this, the vapour tends to get converted back to the liquid phase. To aid this, the atmospheric dust and other compounds act as a [[nucleation]] site and make [[condensation]] possible. The liquid water droplets sticking to dust and particles is known as [[cloud]]s. When enough droplets form and clouds aggregate, [[precipitation]] occurs and it [[rain]]s down back to the land.

=== Is water compressible? ===
Yes, water is a [[compressible fluid]]. For example, the [[density]] of water in the ocean surface is around 1020 kg/m<sup>3</sup>. In smaller volumes the compressibility of the water is negligible. But in a large water body like an ocean, the water compresses itself at deeper regions. The density of water close to the ocean floors can be as high as 1050 kg/m<sup>3</sup>. The [[bulk modulus]] of water is 2.2×10<sup>9</sup> Pa.

=== What happens to water in low pressure? ===
At low pressures, the boiling point of the water will be reduced, which means the water could be boiled at low temperatures. For example, at [[sea level]] the pressure is 1 atm and the water boils at 100 °C. When you take some water to the top of Mount Everest, at 8848 metres altitude the pressure will only be .34 atm. The water there would boil at 71 °C.

=== What happens to water in the vacuum? ===
In near vacuum the pressure is negligible. Due to this the vapour pressure is low and thereby the boiling point is reached instantaneously and the water boils. As the water evaporates, the temperature is lowered, and the water freezes the next moment. When the same thing is repeated in space, the water would again boil due to the lack of pressure and instantly freeze and [[desublimation|desublimate]] due to the lower temperature of -270.45 °C in space.