| Lesson Plan |
| Grade: |
Date: 25/02/2026 |
| Subject: Physics |
| Lesson Topic: recall that, for an elastic collision, total kinetic energy is conserved and the relative speed of approach is equal to the relative speed of separation |
Learning Objective/s:
- Describe the principle of conservation of linear momentum and kinetic energy in elastic collisions.
- Derive and explain why the relative speed of approach equals the relative speed of separation.
- Apply momentum and energy conservation equations to solve quantitative problems involving elastic collisions.
- Compare elastic and inelastic collisions and identify real‑world examples.
- Evaluate student solutions using a worked example and check consistency of relative speeds.
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Materials Needed:
- Projector or interactive whiteboard
- Physics textbook or A‑Level syllabus notes on momentum
- Printed worksheet with derivation steps and worked example
- Set of low‑friction carts and track for a classroom demo
- Motion sensors or video analysis app (optional)
- Calculator or computer algebra system
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Introduction:
Begin with a quick demonstration: two carts on a low‑friction track collide and bounce apart, prompting students to observe that both momentum and kinetic energy appear conserved. Recall the prior lesson on linear momentum conservation and ask learners to predict what should happen to the speeds after an elastic impact. Explain that today’s success criteria are to (i) state the conservation laws for elastic collisions, (ii) derive the relative‑speed relationship, and (iii) solve a problem using both equations.
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Lesson Structure:
- Do‑now (5') – short momentum‑only problem on worksheet.
- Mini‑lecture (10') – review momentum and kinetic‑energy conservation; introduce elastic collision definition.
- Derivation activity (15') – guided step‑by‑step derivation of |u_rel| = |v_rel|; students complete missing steps in handout.
- Demonstration (10') – low‑friction cart collision; students record initial and final speeds with sensors.
- Worked example (10') – walk through the two‑sphere problem, emphasizing simultaneous equations and checking the relative‑speed result.
- Guided practice (10') – pairs solve a similar problem on worksheet; teacher circulates with probing questions.
- Quick check (5') – exit ticket: write the derived speed relationship and give one real‑world example of an elastic collision.
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Conclusion:
Summarise that elastic collisions conserve both momentum and kinetic energy, leading to equal relative speeds before and after impact. Highlight how the derivation links the two conservation laws and how it was confirmed in the demo and example. For homework, assign a set of problems requiring calculation of post‑collision velocities for different mass ratios. Collect exit tickets to gauge immediate understanding.
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