Why does a pulley have a groove 2
What is the purpose of a pulley-wheel ?
•j" I. (b) Read the passage
A very useful kind of wheel is one with teeth, usually called a gear-wheel. Wheels like this can be used to make one part of a machine turn faster or slower than another. The two wheels must have teeth of the samo size, so that they fit together correctly. In fig. 2 the smaller wheel has 20 teeth, and the larger one has 60. If the teeth fit together and the smaller wheel turns once, the larger one will turr one-third of the way round. To male the larger wheel turn once, the smaller must make three-complete turns, in the opposite direction. One of the commones places where gear-wheels may be found is an ordinary watch or clock. If you ca get a broken clock it is not difficult to open it and learn for yourself howit workf Another good example of gear-wheels is found in .a hand-driven sewing machint
