Lesson Plan

• Define the moment (torque) of a force, describe its vector nature and SI unit (N·m).
• Calculate the magnitude of a moment using τ = r F sinθ, identifying the perpendicular component of the force.
• Apply the sign convention and the equilibrium condition (∑τ = 0) to solve static torque problems.
• Analyse common errors such as neglecting perpendicular components or sign conventions.

• Projector or interactive whiteboard
• Whiteboard and markers
• Ruler / metre stick for lever‑arm demonstrations
• Calculator for each student
• Worksheet with practice questions and a diagram handout
• Set of force‑vector cards (optional for group activity)

Begin with a quick demonstration: a wrench turning a bolt to highlight the “turning effect” of a force. Ask students what determines how easy the bolt turns, linking to prior knowledge of force and distance. Explain that today they will be able to state the formal definition of moment, use the correct sign convention, and solve quantitative torque problems.

1. Do‑now (5 '): Students write the definition of torque and list its unit on a sticky note.
2. Mini‑lecture (10 '): Present the vector definition τ = r × F, illustrate the cross‑product with a diagram, and introduce the magnitude formula τ = r F sinθ.
3. Sign‑convention activity (8 '): In pairs, decide positive/negative directions for clockwise and counter‑clockwise moments on a whiteboard sketch.
4. Guided example (12 '): Work through the hinged‑beam problem step‑by‑step, highlighting choice of axis, lever arms, and component forces.
5. Practice stations (15 '): Students rotate through three stations – (a) calculate moments for given forces, (b) identify common mistakes, (c) solve a rotational‑equilibrium problem.
6. Check for understanding (5 '): Quick exit quiz (3 questions) using clickers or paper to confirm mastery of objectives.

Recap the key steps: define torque, find the perpendicular component, apply the sign convention, and set ∑τ = 0 for equilibrium. Students complete an exit ticket stating one mistake to avoid when calculating moments. For homework, assign the three practice questions from the source notes.