Physics · Interactive learning companion

Physics Balancer 2: Torque Balance Simulation

Explain rotational equilibrium through signed torques about the pivot, using the perpendicular distance to the line of action of each force.

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📝 Description

Physics Balancer 2 is a torque and lever-balance simulation. Students place masses at different positions and observe how distance from the pivot affects rotational balance. It supports understanding of moments, torque, equilibrium, and proportional reasoning.

📋 Instructions

Drag masses onto the plank and adjust their positions to balance torque on both sides. Observe how mass and distance work together.

🎓 Learning Guide: Physics Balancer 2: Torque Balance Simulation

Learning focus: Explain rotational equilibrium through signed torques about the pivot, using the perpendicular distance to the line of action of each force.

Physics Interactive learning companion

Learning objectives

Distinguish mass, gravitational force, distance along the plank and the perpendicular lever arm.
Apply the condition that the signed sum of torques about the pivot is zero, including when the plank is inclined.

Concepts and principles

Torque magnitude is τ=rF sinφ=F d⊥, where φ is the angle between the pivot-to-load vector and force, and d⊥ is the perpendicular lever arm.
For a straight plank inclined at angle α to the horizontal, a vertically acting weight mg at distance r along the plank contributes torque magnitude mg r cosα.
For two vertical weights on opposite sides of the same straight plank, their shared cosα factor cancels in ideal static balance. A plank’s own weight or other applied forces can introduce additional torques.

Examples and worked solutions

Two point masses act vertically on opposite sides of an ideal straight plank inclined 30° to horizontal: 2 kg at 3 m from the pivot on the left and mass m at 2 m on the right. Ignore the plank’s own weight. Find m for balance.: Worked solution: Equate opposing moment magnitudes: (2g)(3 cos30°)=(mg)(2 cos30°). The shared g and cos30° factors cancel; m=3 kg.

Try this investigation

Place masses on opposite sides of the pivot and compare their distances measured along the plank.
Predict which side rotates when a mass is moved farther from the pivot, then inspect the game’s torque or angle feedback.
Use the displayed plank inclination to distinguish distance along the plank from the perpendicular lever arm.
Check whether the simulation explicitly includes plank weight or other forces before treating the two-load formula as the complete torque balance.

Expected observations and explanations

A smaller mass farther from the pivot can balance a larger mass nearer to it if their opposing torques have equal magnitudes.
When both vertical weights act on the same rigid straight plank, inclination changes each gravitational moment by the same geometric factor, provided no other moment contributions are present.

Assessment questions and answers

Does placing equal masses on opposite sides necessarily guarantee balance?: Answer: No. Opposing torques depend on the perpendicular distances from the pivot to the force lines of action, not mass alone.