Derailleur gears several standards in use, and in each the product of the derailleur's actuation ratio and the length of cable pulled must equal the pitch of the rear sprockets. The following standards exist. Some rear derailleurs, especially for mountain bikes, incorporate a clutch to keep the lower length of chain in sufficient tension to prevent the chain from striking the bottom of the chain stay, called "chain slap", and which can damage the chain stay. Clutches are also helpful in preventing the chain from derailing from the chain ring on systems without a front derailleur. The front derailleur only has to
Longest word in English Sylvia Plath made mention of it in her semi-autobiographical novel "The Bell Jar", when the protagonist was reading "Finnegans Wake". "Supercalifragilisticexpialidocious", the 34-letter title of a song from the movie "Mary Poppins", does appear in several dictionaries, but only as a proper noun defined in reference to the song title. The attributed meaning is "a word that you say when you don't know what to say." The idea and invention of the word is credited to songwriters Robert and Richard Sherman. The English language permits the legitimate extension of existing words to serve new purposes by the addition of prefixes