a distance S1 of 6 x 2nR, or 94.2 feet. Then, bysubstitution:~60=600x7.85F1X 94.2F1 = 600 x 7.85= 83.3 pounds.94.2 x 0.60Because this machine is only 60-percent efficient,you have to put 94.2 x 83.3, or 7,847 foot-pounds, ofwork into it to get 4,710 foot-pounds of work out of it.The difference (7,847 – 4,710 = 3,137 foot-pounds)is used to overcome friction within the machine.SUMMARYHere are some of the important points you shouldremember about friction, work and efficiency:You do work when you apply a force against aresistance and move the resistance.Since force is measured in pounds and distance ismeasured in feet, we measure work infoot-pounds. One foot-pound of work is theresult of a 1-pound force, acting against aresistance through a distance of 1 foot.Machines help you to do work by making it possibleto move a large resistance through a smalldistance by the application of a small forcethrough a large distance.Since friction is present in all machines, more workmust be done on the machine than the machineactually does on the load.You can find the efficiency of any machine bydividing the output by the input.Friction is the resistance that one surface offers tomovement over a second surface.Friction between two surfaces depends upon thenature of the materials and the size of the forcespushing them together.7-6
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