SIMPLE MACHINES / PULLEY

How does sharing a load across rope segments reduce pulling force?

Change the number of supporting rope segments and compare force and rope travel.

ORIGINAL IDEAL EXAMPLE

200 N load
50 N effort

An ideal continuous rope carries the same tension along its length. Supporting segments share the moving load.

Conceptual schematic; use the model below for parameter-linked geometry.

pulley.napkin / editable

XZ / UNDEFORMED GEOMETRYFITTED TO VIEW

Fixed block selected · related inputs are marked.

pulling force50.00 N✓ passes

BASELINE INPUTS

load200 Nsegments4 28lift200 mm100250

CALCULATED

effort50 N

mechanicalAdvantage4

ropeTravel800 mm

Edits change the baseline source.

THE SOURCE

Edits below update the same model.

# Pulley block: share a load between supporting rope segments
# Scope: Ideal massless frictionless reeving; count only segments supporting the moving block. Block geometry is schematic; rope routing is omitted.
load = 200 N
segments = 4 in 2..8
lift = 200 mm in 100..250
effort := load / segments [N]
mechanicalAdvantage := segments
ropeTravel := lift * segments [mm]
part fixed "Fixed block": box 80 mm, 20 mm, 20 mm at 0 mm, 0 mm, 300 mm
part moving "Moving block": box 80 mm, 20 mm, 20 mm at 0 mm, 0 mm, lift
check pulling force: effort <= 60 N
scenario fewer supporting segments: segments = 2

Calculated from your source · not saved

Baseline · Baseline

pulling force50.00 N ✓ passes

fewer supporting segments · fewer supporting segments

pulling force100.00 N × fails

Calculated from the same .napkin source. Edits preview a temporary study and are not saved.

How the model works

An ideal continuous rope carries the same tension along its length. Supporting segments share the moving load.

effort = load / segments

Try the alternative

More supporting segments reduce pulling force but increase the amount of rope you must pull. Count supporting segments, not simply the number of wheels.

Choose a scenario, change an input, then inspect the equations and force check in Source.

Assumptions and limits

The rope is massless and the pulleys are frictionless. The blocks are schematic; routing, pulley mass, rope stretch, losses and attachment strength are omitted.