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Mechanical Advantage

المؤلف:  GEORGE A. HOADLEY

المصدر:  ESSENTIALS OF PHYSICS

الجزء والصفحة:  p-98

2025-11-05

622

While no machine can give an increase in work, there can be an increase in either speed or force. The ratio of the force overcome as resistance, to the force employed as power, is called the mechanical advantage of the machine with respect to force, provided this ratio is greater than 1; while the ratio of the speed of the resistance, to the speed of the power, is the mechanical advantage in speed, provided this ratio is greater than 1. The mechanical advantage is usually given as it would be if the machine were operated without friction.

For instance, suppose that a machine moves a resistance of 1000 pounds of force a distance of 5 feet, and that the work needed to operate it (in addition to overcoming the friction of the machine) is a force of 100 pounds moving over a distance of 50 feet. The mechanical advantage of force would be the ratio of 1000 to 100; namely, 10. (In actual operation a force of perhaps 110 pounds instead of 100 would be required, in which case the efficiency would Be   or nearly 91 %.)

For any increase in force through the mechanical advantage there is a corresponding decrease in speed, and for any increase in speed there is a corresponding decrease in force. This means again that there can be no gain in the work done through the use of a machine.