| Lesson Plan |
| Grade: |
Date: 25/02/2026 |
| Subject: Physics |
| Lesson Topic: Know that planets, minor planets and comets have elliptical orbits, and recall that the Sun is not at the centre of the elliptical orbit, except when the orbit is approximately circular |
Learning Objective/s:
- Describe Kepler’s First Law and the elliptical shape of planetary orbits.
- Explain why the Sun occupies one focus of an ellipse rather than the geometric centre.
- Compare typical orbital eccentricities of planets, minor planets and comets.
- Predict how orbital shape influences a body’s speed and distance from the Sun.
- Use the ellipse equation to identify semi‑major and semi‑minor axes and calculate the focus distance.
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Materials Needed:
- Projector or interactive whiteboard
- Slide deck with ellipse diagrams
- Handout containing the eccentricity table
- Orbit simulation software (e.g., PhET “Gravity and Orbits”)
- Whiteboard markers
- Exit‑ticket slips
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Introduction:
Begin with a quick animation of planets moving around the Sun, asking students where they think the Sun sits in each path. Recall that students have previously identified circular orbits and can calculate orbital speed. Today they will determine the true shape of Solar System orbits and the Sun’s exact position, using the success criteria displayed on the board.
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Lesson Structure:
- Do‑now (5'): Students label a pre‑drawn ellipse with its centre, foci and axes; teacher checks understanding.
- Mini‑lecture (10'): Explain Kepler’s First Law, introduce the ellipse equation and focus concept using slides.
- Guided practice (12'): Work through the eccentricity table, calculate c = √(a²‑b²) for Earth and Mercury, discuss the Sun’s offset.
- Interactive simulation (10'): Students explore a PhET orbit model, altering eccentricity and observing Sun’s position and speed changes.
- Group task (8'): Each group creates a poster comparing a planet, a minor planet and a comet, highlighting orbit shape and perihelion/aphelion speed differences.
- Check for understanding (5'): Quick quiz (Kahoot) with three conceptual questions.
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Conclusion:
Summarise that all Solar System bodies follow elliptical paths with the Sun at one focus, and only nearly circular orbits allow the Sun to appear central. Students complete an exit ticket stating one implication of orbital eccentricity for observation. For homework, they sketch an ellipse for a chosen comet, label the axes and calculate the focus distance.
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