Pulley block and efficiency
If it saves force, does it also save work?
In a pulley block, n segments of rope share the weight of the load and the movable pulley, so the pull is about 1/n of the total weight; but the free end of the rope has to move n times as far, so no work is saved. Lifting the movable pulley itself is extra work, so the mechanical efficiency is always below 100%; the heavier the load, the higher the efficiency.
Mechanical efficiency vs. load weight
With the movable pulley's weight fixed, the heavier the load, the higher the efficiency — but it never reaches 100%.
Think about it
With the same pulley block, how does the mechanical efficiency change when lifting a heavier load?
It goes up. The extra work (lifting the movable pulley) stays the same while the useful work grows with the load, so η = G/(G + G_pulley) gets closer and closer to 100%. Try changing the load from 20 N to 100 N.
Model assumptionsRope weight and friction ignored · load raised 1 m at constant speed each time
Data log
Set the parameters and click “Record data”. Record several rows with different parameters to plot their relationship and fit a straight line; pause and record at different times to study how a reading changes with time.