The chances are good that a 2-pound force exerted on the handle wouldn t do the job at all. You would need a pull of at least 10 pounds. This shows that only 2 pounds out of the 10 pounds, or 20 percent of the effort, is employed to do the job. The remaining 8 pounds of effort was is in overcoming the friction in the jack. Thus, the jack has an efficiency of only 20 percent.
Most jacks are inefficient.
However, even with this inefficiency, it is possible to deliver a huge push with a small amount of effort. To make the drum revolve once, the pinion gear must rotate six times by the handle, and the handle must turn through a distance S 1 of 6 x 2 p R, or 94.2 feet. Since force is measured in pounds and distance is measured in feet, we measure work in foot-pounds. Machines help you to do work by making it possible to move a large resistance through a small distance by the application of a small force through a large distance. Since friction is present in all machines, more work must be done on the machine than the machine actually does on the load.