Figure 3-4.-Using the capstan.of the axle is L1. Then, EIx LI is the moment of force.You’ll notice that this term includes both the amount ofthe effort and the distance from the point of applicationof effort to the center of the axle. Ordinarily, youmeasure the distance in feet and the applied force inpounds.Therefore, you measure moments of force in foot-pounds (ft-lb). A moment of force is frequently called amoment.By using a longer capstan bar, the sailor in figure3-4 can increase the effectiveness of his push withoutmaking a bigger effort. If he applied his effort closer tothe head of the capstan and used the same force, themoment of force would be less.BALANCING MOMENTSYou know that the sailor in figure 3-4 would landflat on his face if the anchor hawser snapped. As long asnothing breaks, he must continue to push on the capstanbar. He is working against a clockwise moment of forcethat is equal in magnitude, but opposite in direction, tohis counterclockwise moment of force. The resistingmoment, like the effort moment, depends on two factors.In the case of resisting moment, these factors are theforce (Rz) with which the anchor pulls on the hawser andthe distance (L-J from the center of the capstan to its rim.The existence of this resisting force would be clear if thesailor let go of the capstan bar. The weight of the anchorpulling on the capstan would cause the whole works tospin rapidly in a clockwise direction—and good-byeanchor! The principle involved here is that wheneverthe counterclockwise and the clockwise moments offorce are in balance, the machine either moves at asteady speed or remains at rest.This idea of the balance of moments of force can besummed up by the expressionCLOCKWISECOUNTERCLOCKWISEMOMENTSMOMENTSSince a moment of force is the product of theamount of the force times the distance the force actsfrom the center of rotation, this expression of equalitymay be writtenElx ~] =Ezx L2,in thatEI =force of effort,L1=distance from fulcrum or axle to pointwhere you apply force,Ez=force of resistance, andh=distance from fulcrum or center axle tothe point where you apply resistance.EXAMPLE 1Put this formula to work on a capstan problem. Yougrip a single capstan bar 5 feet from the center of acapstan head with a radius of 1 foot. You have to lift a1/2-ton anchor. How big of a push does the sailor haveto exert?First, write down the formulaHereLI=5Ep=1,000 pounds, andL2=l.Substitute these values in the formula, and itbecomes:E1X5=1,000 x 1and= 200 pounds3-3

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