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. Ideal mechanical advantage follows from force balance and conservation of work. Increasing the number of strands supporting a moving block reduces rope tension but increases the length pulled for a given lift. This model compares one, two and four supporting strands. Real friction, rope stretch, wheel masses and nonvertical geometry alter the result.
Engineering and scientific investigation · Discover & try
Why can more supporting rope reduce the pull?
Reading level 4 of 5 · FluentChange
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
The interactive activity is loading.
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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