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Physics
Levers — Lifting with less force
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Move the fulcrum to compare the force needed to lift the same load. Pull the effort handle down or select Lift slowly: the hand goes down as the load rises. Less force means more hand travel.
Drag the fulcrum toward the load
Hand down 0 cm · Load up 0 cm
from the hand end when horizontal
kg
Changing the layout or load starts a new lift.
Raise the load by 15 cm each time
Required force · F
100 N
Direct lifting · P100 N
No force advantage
F/P = 1 · K = 1
Equal forces · equal travel
- Hand down · s
- 0 cm
- Load up · h
- 0 cm
Both rulers measure vertical displacement along the force, not arc length.
Ideal work · extension
Work by the hand0 J
Load potential energy gain0 J
F × s = P × h. Less force requires more hand travel; this ideal model creates no extra energy. Changing the setup or returning to the start begins a new lift.
With moment arms shown, R acts at O and has zero moment about O. The beam pushes the load up; P represents the load pushing the beam down.
Forces act downward on the beam. The controlled slow lift displays ideal balance forces.
Model notes
- A 2 m class-I lever with a rigid, light beam. Beam, joint and tool masses and friction are neglected. Both endpoint forces are vertical and act downward on the beam.
- g = 10 m/s² is a teaching approximation, so weight P = mg. The controls cover loads of 5–20 kg and fulcrum positions 0.5–1.5 m from the hand end of the horizontal beam.
- The controlled slow lift is a sequence of nearly balanced configurations: F × dE = P × dB. The animation does not predict real lifting time, acceleration or human strength. Starting and stopping in reality need a moment difference and involve losses.
- a and b are lengths along the beam; perpendicular moment arms are dE = a cosθ and dB = b cosθ. Do not extend F = Pb/a to oblique forces, a heavy beam or a fulcrum beyond the endpoints.
- Each lift raises the load by 15 cm. Hand travel s and load rise h are vertical displacements along the forces, not arc lengths. Ideal work F × s = P × h; moving the fulcrum and resetting do not count as lifting work.
- The drawn load size does not encode mass; the kg label and P arrow length show the load. Force arrows share one linear scale, and displacement rulers share one geometric scale.