Figure 1-1.-A simple lever.operation of complex machines. Complex machines aremerely combinations of two or more simple machines.THE LEVERThe simplest machine, and perhaps the one withwhich you are most familiar, is the lever. A seesaw is afamiliar example of a lever in which one weightbalances the other.You will find that all levers have three basic parts:the fulcrum (F), a force or effort (E), and a resistance(R). Look at the lever in figure 1-1. You see the pivotalpoint (fulcrum) (F); the effort (E), which is applied at adistance (A) from the fulcrum; and a resistance (R),which acts at a distance (a) from the fulcrum. DistancesA and a are the arms of the lever.CLASSES OF LEVERSThe three classes of levers are shown in figure 1-2.The location of the fulcrum (the fixed or pivot point) inrelation to the resistance (or weight) and the effortdetermines the lever class.First ClassIn the first class (fig. 1-2, part A), the fulcrum islocated between the effort and the resistance. Asmentioned earlier, the seesaw is a good example of afirst-class lever. The amount of weight and the distancefrom the fulcrum can be varied to suit the need.Notice that the sailor in figure 1-3 applies effort onthe handles of the oars. An oar is another good example.The oarlock is the fulcrum, and the water is theresistance. In this case, as in figure 1-1, the force isapplied on one side of the fulcrum and the resistance tobe overcome is applied to the opposite side; hence, thisis a first class lever. Crowbars, shears, and pliers arecommon examples of this class of levers.Second ClassThe second class of lever (fig. 1-2, part B) has thefulcrum at one end, the effort applied at the other end,and the resistance somewhere between those points. TheFigure 1-2.-Three classes of levers.Figure 1-3.-Oars are levers.wheelbarrow in figure 1-4 is a good example of asecond-class lever. If you apply 50 pounds of effort tothe handles of a wheelbarrow 4 feet from the fulcrum(wheel), you can lift 200 pounds of weight 1 foot fromthe fulcrum. If the load were placed farther away fromthe wheel, would it be easier or harder to lift?Levers of the first and second class are commonlyused to help in overcoming big resistances with arelatively small effort.Third ClassSometimes you will want to speed up the movementof the resistance even though you have to use a largeamount of effort. Levers that help you accomplish thisare in the third class of levers. As shown in figure 1-2,part C, the fulcrum is at one end of the lever, and the1-2
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