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Which Animals Use Jet Propulsion?
Jet propulsion is motion produced by passing a jet of fluid (e.g. air or water) in the opposite direction to the direction of motion. By conservation of momentum, the moving body is propelled in the opposite direction to the jet.
A number of animals, including cephalopods, sea hares, arthropods and fish have convergently evolved jet propulsion mechanisms. These have been artificially mimicked by the jet engine.
In a pumping action, a jellyfish draws water into its bell and then contracts to force it out. The water is expelled in one direction, and the jellyfish moves in the other. But jet propulsion is not exclusive to jellyfish. Scallops clap their shells together to force out water, speeding away from the probing arm of a starfish or from another predator.
On the underside of a squid’s body is a funnel-shaped tube through which a spurt of water can be released. By turning the nozzle forward, backward, or to either side, this torpedo-shaped mollusk can control its direction as it streaks through the water as fast as 20 miles an hour. Some squid build up their velocity and then explode from the surface, shooting up into the air.
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