Classes of Levers

Figure 1-1.-A simple lever. operation of complex machines. Complex machines are merely combinations of two or more simple machines. THE LEVER The simplest machine, and perhaps the one with which you are most familiar, is the lever. A seesaw is a familiar  example  of  a  lever  in  which  one  weight balances 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 pivotal point (fulcrum) (F); the effort (E), which is applied at a distance (A) from the fulcrum; and a resistance (R), which acts at a distance (a) from the fulcrum. Distances A and a are the arms of the lever. CLASSES OF LEVERS The three classes of levers are shown in figure 1-2. The location of the fulcrum (the fixed or pivot point) in relation to the resistance (or weight) and the effort determines the lever class. First Class In the first class (fig. 1-2, part A), the fulcrum is located  between  the  effort  and  the  resistance.  As mentioned earlier, the seesaw is a good example of a first-class lever. The amount of weight and the distance from the fulcrum can be varied to suit the need. Notice that the sailor in figure 1-3 applies effort on the handles of the oars. An oar is another good example. The  oarlock  is  the  fulcrum,  and  the  water  is  the resistance. In this case, as in figure 1-1, the force is applied on one side of the fulcrum and the resistance to be overcome is applied to the opposite side; hence, this is a first class lever. Crowbars, shears, and pliers are common examples of this class of levers. Second Class The second class of lever (fig. 1-2, part B) has the fulcrum at one end, the effort applied at the other end, and the resistance somewhere between those points. The Figure 1-2.-Three classes of levers. Figure 1-3.-Oars are levers. wheelbarrow  in  figure  1-4  is  a  good  example  of  a second-class  lever.  If  you  apply  50  pounds  of  effort  to the handles of a wheelbarrow 4 feet from the fulcrum (wheel), you can lift 200 pounds of weight 1 foot from the fulcrum. If the load were placed farther away from the wheel, would it be easier or harder to lift? Levers of the first and second class are commonly used  to  help  in  overcoming  big  resistances  with  a relatively  small  effort. Third  Class Sometimes you will want to speed up the movement of the resistance even though you have to use a large amount of effort. Levers that help you accomplish this are in the third class of levers. As shown in figure 1-2, part C, the fulcrum is at one end of the lever, and the 1-2


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