Balance Is Torque, Not Weight

You'll learnthat a plank balances when torques cancel, not when the weights match.

A 40 N kid far out balances a 60 N kid sitting close — because a plank holds still when the torques cancel, not when the weights match. Torque is force times lever arm, it carries a sign, and full equilibrium keeps two books at once: ΣF = 0 and Στ = 0.

8 STEPS · 6 QUICK CHECKS · v2

STATICS LAB

Before you start

What you're looking at

A plank on a pivot: a 40 N kid sits 3 m left of it, a 60 N kid sits 2 m right of it.

The question

With unequal weights at unequal distances, does the plank balance or tip?

Watch for

The torque needle below. The heavier kid does not decide it — each torque is weight times its arm.

What the symbols mean

τ = force × lever arm, with a sign: green CCW is +, red CW is −; balance means Στ = 0.

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