Derailleur gears by 13 drive-train. Most road bicycles have two chainrings, and touring bicycles commonly have three. The rear derailleur serves double duty: moving the chain between rear sprockets and taking up chain slack caused by moving to a smaller sprocket at the rear or a smaller chainring by the front derailleur. In order to accomplish this second task, it is positioned in the path of the bottom, slack portion of chain. Sometimes the rear-derailleurs are re-purposed as chain tensioners for single-speed bicycles that cannot adjust chain tension by a different method. Although variations exist, as noted below, most rear derailleurs have
Word sort certain elements, young children make sense of words and patterns within words. Word sorts combine both constructivist learning and teacher-directed instruction. Students receive a stack of cards containing either pictures or words that have several types of contrasting sounds, patterns, or meanings. Each student must then figure out the patterns that exist within the stack, and sort the cards accordingly. By doing this, students construct their own knowledge of words, creating a lasting understanding of how language works. This process contrasts greatly to the simple memorization related to traditional spelling tests. The more students understand about the structure of words