How a pulley divides the load
A pulley does not make a load weigh less. In a movable-pulley system, the load hangs from a block supported by several rope segments. If the rope is ideal—light and frictionless—the tension is nearly the same throughout it. Each supporting segment therefore carries part of the load, so the pull at the free end can be smaller than the load’s weight.
Count the rope segments that directly support the moving load, not every wheel in the setup. With two supporting segments, for example, each carries roughly half the load. A fixed pulley, by contrast, mainly changes the direction of the pull: it lets someone pull downward while lifting upward, but by itself it does not divide the load among extra supporting segments.
Why the rope has to travel farther
The tradeoff follows from the geometry. When the load rises, every supporting segment gets shorter. If there are several segments sharing the load, the free end must move enough rope to shorten all of them. Two supporting segments mean roughly twice as much rope must be pulled as the load rises; four mean roughly four times as much.
That is mechanical advantage: exchanging a longer movement for a smaller force. In an ideal system, the work put in—force multiplied by distance—matches the work done lifting the load. The pulley changes how that work is delivered, not how much is required.
Real pulleys add resistance
Actual rope bends around wheels, and axles and rope surfaces create friction. Some of the pull is spent overcoming that resistance, so the required force is greater than the ideal calculation predicts. The practical benefit remains: a person can lift a load that would be difficult to raise directly, by pulling more rope over a longer distance.
That is why a pulley system can make a heavy object manageable without making the lifting task effortless.
