In levers of the first class, the fulcrum is placed between the acting and resisting forces as shown in Fig. 10.
This figure illustrates the lifting of a heavy block by means of a crowbar and a support.
E = Effort F = Fulcrum W = Weight
By pressing down the end of the bar E the other end of the lever raises the weight W and the center of motion is at the fulcrum F. In other words, the applied force E acting on the lever supported by the fulcrum F overcomes the resistance, called weight W.
The force of the lifting power of the lever increases in proportion as the distance of the effort E from the fulcrum increases, and diminishes in proportion as the distance of the weight W from the fulcrum increases.
FIG10. - A Lever of the First Class.
* It should be noted that when leverage problems are figured by arithmetic no account is taken of the weight of the lever itself. The results obtained by using simply weights and distances are exact enough for all practical purposes. If the designer had to allow for the weight of the lever itself, he would have to make a long and difficult calculation. Such allowance, however, is not necessary because, for safety, all parts of machinery are made at least five times as strong as they need to be.