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| {{otheruses}}
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| <!-- [[Image:Metal whistle.jpg|thumb|250px|A metal whistle]] -->
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| A '''whistle''' is a one-note [[woodwind]] [[musical instrument|instrument]] which produces [[sound]] from a stream of forced air. (For the sound produced with the mouth, see [[whistling]] and [[whistled language]].)
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| Many types exist, from small [[police]] and [[sports]] whistles (also called [[pea whistles]]), to much larger [[train whistle]]s, which are [[steam whistle]]s specifically designed for use on [[locomotive]]s and [[ship]]s. Although whistles have a musical characteristic (for example train whistles sound a minor-seventh musical chord) whistles are not usually considered 'musical' in the sense of being able to play a chosen melody, but mainly the small whistles can also be used as a - very shrill and loud - [[noise instrument|noise]] and [[rhythm instrument]]. However, musical whistles exist, including any of several 2-[[octave]] musical instruments known as [[tin whistle]]s (sometimes known as pennywhistles or low whistles), as well as the [[calliope (music)|calliope]] (an array of separately actuable steam whistles), [[Organ (music)|organ]] pipes and the [[recorder]]. Pea whistles are used in [[jazz]] and [[Latin music]] as a [[percussion instrument]].
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| The whistle works by causing the smooth flow of air to be split by a narrow blade, sometimes called a [[fipple]], creating a [[turbulence|turbulent]] [[vortex]] which causes the air to vibrate. By attaching a [[Acoustic resonance|resonant]] chamber to the basic whistle, it may be tuned to a particular note and made louder. The length of the chamber typically defines the resonant [[frequency]]. A whistle may also contain a small light ball, usually called the ''[[pea]]'', which rattles around inside, creating a [[chaos|chaotic]] [[vibrato]] effect that intensifies the sound. [[Japanese people|Japanese]] [[bird whistles]] use several small balls and are half filled with water in order to reproduce the sound of a [[bird song]].
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| A steam whistle works the same way, but using steam as a source of pressure: such whistles can produce extremely high sound intensities.
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| Sometimes, unintentional whistles can be set up. A common one is the opened [[sunroof]] of a [[Automobile|car]]: air passing over the top of the vehicle can, at certain speeds, strike the back edge of the sunroof, creating a very low frequency whistle which is resonated by the closed interior of the car. Since the sound frequency is [[infrasonic]], around 4 [[Hertz|Hz]], the effect is very uncomfortable for occupants, who feel the vibration rather than hear it. Such low frequencies can induce [[nausea]], [[headache]], [[delirium|disorientation]] and [[dizziness]]. The effect can be prevented by opening a side window a few inches. Subsonic whistles have also been developed for use as weapons, or to deliberately create a sense of uneasiness in an enemy.
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| ==Industrial whistles==
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| [[Image:Police whistles.jpg|thumb|250 px|Examples of police whistles]]
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| Industrial whistles are used for [[Distress signal|signal]]ling and [[time|timekeeping]] both on [[railroad]] and [[ship]]s, and in [[factory|factories]]. Most of these whistles were [[steam power]]ed and not standardized. Individual [[locomotive]]s could be identified by their whistles. At noontime in industrial areas up into the [[1950s]] whistles of every pitch could be heard, as each factory had a boiler and a whistle, if not full steam power.
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| Railroads in particular used elaborate whistle codes for communication both within the [[train]] and with other trains. These methods are maintained today with motor-powered [[air horn]]s. Trucks also use air horns, especially since they often have air brakes and so there is already a source of compressed air on board.
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| [[Train whistle]]s generally produce three or four different frequencies at the same time, to produce a non-[[major chord]], that is distinct, loud, and low in pitch.
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| ==Safety==
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| Whistles are often used as warning devices or as safety devices serving to attract attention to the user. Some [[cyclist]]s use a whistle as a substitute for a [[bell (instrument) | bell]] or [[Horn (acoustic)|horn]]. It should be noted, however, that many jurisdictions require that the warning device be permanently attached to the [[bicycle]].
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| Rescue or Survival whistles are often packed in [[survival kit]]s and attached to [[Personal flotation device]]s to allow a victim to signal for help. The whistle is audible at much greater distances than the human voice, and is less likely to cause exhaustion if used repeatedly. Survival whistles differ from pea whistles in that they are usually flat, so that water cannot collect inside if the user is immersed, for example after falling overboard from a boat.
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| [[Category:Flutes]]
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| [[Category:Hiking equipment]]
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| [[es:Silbato]]
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| [[fr:Sifflet]]
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| [[nl:Fluitje (blaasinstrument)]]
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| [[ja:ホイッスル]]
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| [[ug:دۈدۈت]]
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| [[pl:Gwizdek]]
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| [[pt:Apito]]
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| [[ru:Свисток]]
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| [[simple:Whistle]]
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| [[sv:Visselpipa]]
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