The single moving pulley
This is shown in Fig. 8.4. Here the tension in the string or rope is equal to the effort applied, so that the total upward pull on the pulley is twice the effort E. Suppose a load of 4 N is supported by the pulley and that the weight of the pulley block and string is negligible. Then, since the load is supported by the tension in two sections of string, the effort applied need only be 2 N.