By Zencalcy Editorial TeamLast reviewed About us
A seesaw balances when the clockwise and counter-clockwise moments about the pivot are equal. Since each moment is mass times distance, a lighter person can balance a heavier one simply by sitting farther from the pivot.
Balance a lever with unequal masses or distances.
m₁ d₁ = m₂ d₂
d₁ and d₂ are horizontal distances from the pivot. The formula ignores the plank's own weight; for a uniform plank, treat its mass as acting at the midpoint.
| Symbol | Meaning |
|---|---|
| m₁, m₂ | Masses on either side of the pivot, in kilograms. |
| d₁, d₂ | Distances from the pivot, in metres. |
30 × 2 = 60 kg·m on one side, and 20 × 3 = 60 kg·m on the other. The moments match, so the plank is in balance.
Continue with the Torque Calculator, Beam Reaction Calculator, or the Center of Mass Calculator — or browse more statics tools and all physics calculators.
No, only the distances from the pivot to each mass. A longer plank simply gives more room to place them.
Results are computed from the standard equations of classical mechanics. Unit conversions use the SI definitions published by NIST. Air resistance is ignored unless the calculator names a drag model.
Reference material used to build and check this calculator:
Last reviewed: September 2026. See how we build and check every tool on the about page.
Free calculator · No signup
Free calculator · No signup
Free calculator · No signup
Free calculator · No signup
Free calculator · No signup
Free calculator · No signup
Content updated: September 2026