A pulley block uses one rope and a pair of wheels to lift a heavy load with a smaller pull. This diagram shows a fixed pulley on the beam and a movable pulley on the load, and lets you watch the rope runs share the weight.
A pulley block is a way of lifting a load with less effort by spreading its weight over more than one section of rope. It is built from a single rope threaded around two wheels: a fixed pulley bolted to an overhead beam, and a movable pulley that hangs on the rope and travels up and down with the load.
Unlike a lever or a ramp, a pulley block does not rely on a long arm or a gentle slope. It works simply by giving the load several rope runs to hang from, so no single run has to carry the whole weight.
Follow the rope from where it is tied to the beam: down to the movable pulley, around it, back up over the fixed pulley, and then down to the free end you pull. The two arrows marked T show the rope pulling up on the movable pulley from both sides — together they hold up the load.
One end of the rope is tied to a fixed point on the beam. This end never moves, so it gives the movable pulley a fixed anchor to pull against.
The rope runs down, around the wheel that carries the load, and back up. Because it wraps right around, the pulley is held up by two sections of rope at once.
The top pulley is bolted to the beam so its axle cannot move. It does not reduce the force — it simply redirects the rope so you can pull downward instead of lifting straight up.
Both sections of rope pulling on the movable pulley carry part of the weight. With two runs, each carries about half of W, so the tension in the rope you pull is roughly half the load.
You pull down on the free end and the load rises. Because the rope is shared, you must draw in about twice as much rope as the load climbs — half the force, but twice the distance.
No. A single fixed pulley only changes the direction of your pull. You must still pull with a force equal to the load; the only benefit is that you can pull downward more easily.
Because the load hangs from two sections of rope. Each section carries about half the weight, so the rope you pull only needs about half the force.
Distance. To raise the load one metre you must pull roughly two metres of rope through the pulley, so the work done stays the same.
Count the sections of rope pulling up on the movable pulley — in this diagram, two. The effort is roughly the load divided by that number of runs.
Yes. Real pulleys have friction in the axles and the rope, so a little extra effort is always needed and the saving is a bit less than the ideal count suggests.