Levers, Torque & Balance
Read lever diagrams, predict turning direction, compare moments, and solve balance problems using force × distance.
Levers, Torque & Balance
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What makes a lever turn?
The pivot is the point the lever rotates around.
Down on the left tends counterclockwise; down on the right tends clockwise.
The same force has a greater turning effect farther from the fulcrum.
For perpendicular forces, M = Fd, in N·m.
Total clockwise moment = total counterclockwise moment.
For masses on a seesaw, m₁d₁ = m₂d₂ because the same g is on both sides.
PIVOT → SIDE → PRODUCT
Fast check: a smaller force can balance a larger one only if it acts farther from the fulcrum.
See the mechanism before the equation
Common traps
Comparing forces only: distance matters too. Using total lever length: measure each arm from the fulcrum. Ignoring direction: opposite moments oppose each other. Multiplying every mass by g: for a balance of masses in the same gravity, g cancels.
Can you handle all five forms?
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Quick clarifications
Torque or moment? Here, both describe the turning effect of a force about a pivot. Use force × perpendicular distance.
Do I always need an equation? No. Direction and qualitative force-distance questions are often faster by inspection.
Why can kg be used on both sides of a seesaw? Each weight is mg; the same g cancels.
Several forces on one side? Add their moments, keeping clockwise and counterclockwise effects separate.
Continue Mechanical Reasoning
Gears & Gear Trains · Pulleys & Mechanical Advantage · Belts, Chains, Racks & Connected Wheels · Wheels & Axles · Forces, Friction & Equilibrium
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