What is Air?
[[File:Kawasaki-Electric Fan.jpg|thumb|A [[wikt:fan|fan]] moves air.]] '''Air''' is the [[Earth]]'s [[atmosphere]]. Air is a [[mixture]] of many gases and tiny dust particles. It is the clear [[gas]] in which living things live and [[breathe]]. It has an indefinite shape and [[volume]]. It has [[mass]] and [[weight]], because it is [[matter]]. The weight of air creates [[atmosphere pressure|atmospheric pressure]]. There is no air in [[outer space]]. Earth's atmosphere is composed of about 78 percent nitrogen, 21 percent oxygen, 0.9 percent argon, and 0.1 percent other gases. Animals live and need to breathe the oxygen in the atmosphere. In [[breathing]], the [[lung]]s put oxygen into the [[blood]], and send back [[carbon dioxide]] to the air. Plants need the carbon dioxide in the air to live. They give off the oxygen that we breathe. Without it animals die of [[asphyxia]]. Air can be [[air pollution|polluted]] by some gases (such as [[carbon monoxide]], hydrocarbons, and nitrogen oxides), [[smoke]], and ash. This [[air pollution]] causes various problems including [[smog]], [[acid rain]] and [[global warming]]. It can damage people's [[health]] and the environment. There are debates about whether or not to act upon climate change, but soon enough the Earth will heat up too much, causing it to become too hot and not support life. Some say fewer people would die of cold weather, and that is true but there is already a huge amount of people dying from heat and that number is and will keep increasing more and more. Since early times, air has been used to create [[technology]]. Ships moved with sails and windmills used the mechanical motion of air. Aircraft use [[propeller]]s to move air over a [[wing]], which allows them to [[flight|fly]]. [[Pneumatics]] use [[air pressure]] to move things. Since the late 1900s, air power is also used to generate electricity. Air is invisible: it cannot be seen by the eye, though a shimmering in hot air can be seen.<ref>{{cite web | url=https://www.sciencefocus.com/planet-earth