Editing Water rocket (section)

== Operation ==
[[File:Water rocket.gif|thumb|left|Simplified animation of how a water rocket works.<br />1) A bubble of compressed air is added and pressurizes the contents of the bottle.<br />2) The bottle is released from the pump.<br />3) The water is pushed out through the nozzle by the compressed air.<br />4) The bottle moves away from the water because it follows [[Newton's third law]].]]
The bottle is partly filled with water and sealed. The bottle is then pressurized with a gas, usually air compressed from a [[bicycle pump]], [[air compressor]], or cylinder up to 125 psi, but sometimes CO<sub>2</sub> or [[nitrogen]] from a cylinder are used.
[[File:WaterRocketLaunch.jpg|thumb|right|upright|Launch of a bottle without nose cone or fins.]]
[[File:WaterRocket.JPG|thumb|right|Launching a water rocket. The rocket is in its peak with no water inside it.]]

Water and gas are used in combination, with the gas providing a means to store energy, as it is compressible, and the water increasing the [[propellant mass fraction]] and providing greater force when ejected from the rocket's nozzle. Sometimes additives are combined with the water to enhance performance in different ways. For example: salt can be added to increase the density of the reaction mass, resulting in a higher [[delta-v]]. Soap is also sometimes used to create a dense foam in the rocket which lowers the density of the expelled reaction mass but increases the duration of thrust.

The seal on the nozzle of the rocket is then released and rapid expulsion of water occurs at high speeds until the propellant has been used up and the air pressure inside the rocket drops to atmospheric pressure. There is a net force created on the rocket in accordance with [[Newton's third law]]. The expulsion of the water thus can cause the rocket to leap a considerable distance into the air.

In addition to aerodynamic considerations, altitude and flight duration are dependent upon the volume of water, the initial pressure, the rocket [[nozzle]]'s size, and the unloaded weight of the rocket. The relationship between these factors is complex and several simulators have been written to explore these and other factors.<ref>{{cite web|url=http://exploration.grc.nasa.gov/education/rocket/BottleRocket/sim.htm|archive-url=https://web.archive.org/web/20060207020049/http://exploration.grc.nasa.gov/education/rocket/BottleRocket/sim.htm|url-status=dead|archive-date=2006-02-07|title=Water Rocket Computer Model |publisher=[[NASA]]|website=nasa.gov}}</ref><ref>[http://www.et.byu.edu/~wheeler/benchtop/sim.php Sim Water Rocket] {{Webarchive|url=https://web.archive.org/web/20130728082910/http://www.et.byu.edu/~wheeler/benchtop/sim.php |date=2013-07-28 }} from Dean's Benchtop</ref>

[[File:Water rocket liftoff slow motion.mpg|thumb|Full HD 40 times slow motion video of water rocket liftoff]]
Often the pressure vessel is built from one or more used plastic soft drink bottles, but polycarbonate fluorescent tube covers, plastic pipes, and other light-weight pressure-resistant cylindrical vessels have also been used.

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