The water cycle is the process of continuous phase changes of water on a planet like Earth. It explains how liquid water moves from the ocean to the atmosphere as water vapour and how it falls back to the land and continues the cycle. The cycle begins with the water in its liquid phase of matter mostly on the surface of the ocean, where it is heated by the Sun. Liquid water, when its temperature increases, it evaporates faster and changes to the gaseous phase called water vapour. This warm vapour rises in the atmosphere while it expands and cools with the altitude. When cooled enough, the water vapour loses energy. The atmosphere has other particles and dust floating around too. So these particulates suspended in the atmosphere acts as nucleation sites and lead to the condensation of the water vapour back into liquid water droplets. These suspended liquid droplets in the atmosphere is just known as clouds. When the droplets increase in size, they fall back to the surface of the planet due to gravity as rain, also known as precipitation. The water finds a reservoir and then flows back to the oceans to continue the cycle.
Frequently Asked Questions
Why rain water is not salty when it is evaporated from the ocean that has salty water?
The salty ocean water that contains sodium and chloride ions that do not have enough energy to evaporate at the standard temperature at the surface of the ocean. Therefore, water that evaporates from the oceans as vapour will only contain water molecules in it. The same happens in distillation of water.
What causes acid rain?
Acid rain is caused when the rainwater that falls from the clouds reacts with the compounds like nitrogen oxide and sulfur dioxide in the air. These compounds decrease the pH value of the rain and make it more acidic in nature. Naturally, rain is a little acidic as it reacts with carbon dioxide in the atmosphere to form carbonic acid. But it is due to the industrial revolution and other human activities like fossil fuel burning, the concentration of the other pollutants like sulfur dioxide and nitrogen oxide have increased to cause rain that is highly acidic in nature. Other sources of these pollutants include natural events like lightning and volcanic eruptions.