A pulley arrangement can make lifting easier by sharing a load across more rope strands. The smaller pull has a trade-off: more rope must move. In the ideal model, two supporting strands halve the pull but double the rope travel. The energy needed has not disappeared. With equal tension in an ideal continuous rope, the supporting vertical strands supply a combined upward force. Quasistatic balance gives pull equal to load divided by strand count; kinematic rope-length conservation requires the free end to travel that many times the load displacement. Together, the ideal force and distance relationships conserve the work transferred by the rope.
Engineering and scientific investigation · Discover & try
Why can more supporting rope reduce the pull?
Reading level 5 of 5 · AdvancedChange
Word help
Mechanical advantage
The ratio of output load force to input force.
Supporting strand
A rope segment pulling upward on the moving load.
Watch · Try · Explain
See how it works
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Massless rope, negligible friction and equal vertical tensions. Model loads and distances illustrate the force–distance trade-off.
What to look for
- You pull with 80 model N and move the rope the same distance as the load rises.
- The pull falls to 40 model N, but rope travel doubles.
- The pull is 20 model N, and rope travel is four times the rise.
Explain what you noticed
For the same load and rise, what changes when an ideal system goes from two supporting strands to four?
Keep this idea: An ideal pulley trades lower force for greater rope travel; it does not create free work.
Follow the sources
- University of Colorado Boulder / TeachEngineering — Powerful Pulleys
- University of Colorado Boulder / TeachEngineering — The Power of Mechanical Advantage
Source material checked 2026-10-29. Explanations and activities by Nepedia. Source links do not imply endorsement.
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