| Lesson Plan |
| Grade: |
Date: 25/02/2026 |
| Subject: Physics |
| Lesson Topic: understand that the weight of an object may be taken as acting at a single point known as its centre of gravity |
Learning Objective/s:
- Describe the concept of centre of gravity and how it represents the weight of an object.
- Apply the torque formula τ = rF to calculate turning effects using the centre of gravity.
- Determine the centre of gravity of simple and irregular bodies using symmetry or suspension methods.
- Analyse given scenarios to compute net torque about a pivot.
- Explain how the centre of gravity shifts for non‑uniform objects.
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Materials Needed:
- Projector or interactive whiteboard
- Physics textbook or handout on torque and centre of gravity
- Worksheets with practice problems
- Uniform rods, rectangular plates, and a beam for hands‑on demonstration
- String and small weights for suspension experiment
- Calculator or computer simulation software
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Introduction:
Begin with a quick demonstration: suspend a ruler from a point and ask students where it balances, sparking curiosity about a hidden point. Recall previous work on forces and moments, emphasizing that weight acts uniformly in a gravitational field. Explain that today’s success criteria are to locate a centre of gravity, use it to simplify torque calculations, and solve real‑world problems.
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Lesson Structure:
- Do‑now (5'): Students answer a short torque question from the previous lesson.
- Mini‑lecture (10'): Define centre of gravity, relate it to weight, and present the torque formula.
- Guided demonstration (10'): Teacher suspends an irregular object, draws CG lines, and discusses the result.
- Group activity (15'): Teams locate the CG of rods and plates by symmetry and by suspension, recording measurements.
- Worked example (10'): Solve the beam‑pivot problem on the board, highlighting the use of the CG.
- Independent practice (15'): Students complete a worksheet with three practice questions while the teacher circulates.
- Exit ticket (5'): One‑sentence response to “Why can we treat weight as a single force at the CG?”
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Conclusion:
Summarise that treating weight at the centre of gravity streamlines torque analysis and that the perpendicular lever arm determines the turning effect. Invite a few students to share their exit‑ticket answers to verify understanding. Assign homework: complete a worksheet calculating torques for two additional objects and reflect on how the centre of gravity shifts for a non‑uniform item.
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