Loop a rope through wheels and the weight gets shared across several strands, so each pull feels lighter — though you reel in more rope.
What's actually happening
A single fixed pulley — a wheel bolted to the ceiling with a rope over it — multiplies nothing. Pull down one metre, the load rises one metre, with the same force. What you bought is direction: pulling down is easier on a human body than hauling up, because you can hang your weight on the rope. Flagpoles and window blinds settle for exactly this.
The multiplication starts when a pulley moves with the load. Hang the load from a pulley wheel, run the rope under it and back up, and now two strands of rope share the hanging. Tension is the same everywhere in one rope, so each strand carries half — your pull only needs to beat half the weight. Add wheels and weave the rope back and forth (a block and tackle) and four, six, eight strands each carry their share. Effort equals load divided by the number of strands holding it up. With six strands, a piano feels like a heavy suitcase.
The bill arrives as rope. To raise the load one metre, every one of those six supporting strands must shorten by a metre — and all that slack passes through your hands. Six times less force, six times more pulling. Work, force times distance, is untouched; the pulley is a currency exchange, not a money printer. Cranes accept the deal happily: their motors spool kilometres of cable through many-stranded blocks because cable is cheap and force is not.
- 1Two people hold two broomsticks horizontally, a metre apart. Tie a rope to one stick and weave it between the two sticks three or four times.
- 2Have both holders pull the sticks apart as hard as they can while you pull the rope's free end.
- 3You win easily. Every wrap adds strands sharing the load — with four wraps you are out-pulling two people with one hand.