The arrangement in Example 4.2 (p. 95) makes it possible to amplify a force. (Compare this example to the block and tackle in Fig. 3.23.) Amplifying forces in this way comes at a price. To appreciate this price, imagine that the force on the car in Figure 4.4 is just barely large enough to move the car. If the car begins to move, point O on the cable also begins to move. Calculate the ratio of the distance moved by the car to the distance moved by point O and compare it to the force amplification factor found in Example 4.2. Assume the car moves in the direction of the tension force; that is, assume it moves along the direction defined by the cable.

Figure 3.23

Tension = 2T 27 Tension forces on only the pulley 27 B