can a man weighing 200 pounds lift a load three times above his weight with ease?
a. Consider first the heavy block in the diagram below suspended from two ropes. The upward force on the block is the tension in the ropes, and the sum of the two tensions must equal the weight of the block. If the whole system is symmetrical, each rope is under tension equal to half the weight of the block.
b. Now look at the diagram below where the block has been attached to a pulley. There is now only one rope, which passes through the pulley. The tension in the rope is the same throughout; if it were different on one side than on the other, the pulley would turn until the tension on the two sides equalized. The tension in the rope is still only half the weight of the block.
c. The Work Principle
(1) Webster's definition of work states that; work is an activity in which one exerts strength or faculties to do or perform something. It is a sustained physical or mental effort to overcome obstacles and achieve an objective or result. What kind of advantage can we achieve using Pulley systems to reduce the amount of work we do?
(2) While pulleys are useful, they do not give something for nothing. Ignoring the problem of friction (force which opposes the movement of one surface sliding or rolling over another with which it is in contact), the input and output forces are in inverse ratio to the respective distance. To solve this we use this formula:
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