Rapids are sections of a river where the river bed has a relatively steep gradient, causing an increase in water velocity and turbulence. Rapids are hydrological features between a run (a smoothly flowing part of a stream) and a cascade. Rapids are characterised by the river becoming shallower with some rocks exposed above the flow surface. As flowing water splashes over and around the rocks, air bubbles become mixed in with it and portions of the surface acquire a white colour, forming what is called "whitewater". Rapids occur where the bed material is highly resistant to the erosive power of the stream in comparison with the bed downstream of the rapids. Very young streams flowing across solid rock may be rapids for much of their length.
Rapids are categorized in classes, generally running from I to VI. A Class 5 rapid may be categorized as Class 5.1-5.9. While class I rapids are easy to negotiate and require no maneuvering, class VI rapids pose threat to life with little or no chance for rescue.
Società Torinese Automobili Rapid, also known as S.T.A.R. and Rapid, was an Italian car manufacturer founded by Giovanni Battista Ceirano in Turin in July 1904. Rapid was its trademark. In 1921 it was acquired by the S.P.A. (Società Piemontese Automobili) company that had been founded by Giovanni Battista's brother Matteo Ceirano, and which, in 1925, was taken over by Fiat.
The Ceirano brothers, Giovanni Battista, Giovanni, Ernesto and Matteo, were influential in the founding of the Italian auto industry, being variously responsible for : Ceirano; Welleyes (the technical basis of F.I.A.T.); Fratelli Ceirano; S.T.A.R. / Rapid (Società Torinese Automobili Rapid); SCAT (Società Ceirano Automobili Torino); Itala and S.P.A. (Società Piemontese Automobili). Giovanni's son Giovanni "Ernesto" was also influential, co-founding Ceirano Fabbrica Automobili (aka Giovanni Ceirano Fabbrica Automobili) and Fabrica Anonima Torinese Automobili (FATA).
A rapid is a section of a river with turbulent water flow.
Rapid may also refer to: