Lesson Plan

• Describe Newton’s law of universal gravitation and identify each variable.
• Explain how the Sun’s gravitational force supplies the centripetal force required for orbital motion.
• Calculate orbital speed or period for a planet using the derived formulas.
• Identify and correct common misconceptions about gravity in space.

• Projector and screen
• Whiteboard and markers
• Printed worksheet with orbital‑speed problems
• Scientific calculators
• Diagram or 3‑D model of the Sun and planets
• Computer with an interactive gravity simulation (e.g., PhET)

Begin with a striking image of planets circling the Sun and ask, “What keeps them from flying away?” Recall students’ prior knowledge that gravity pulls objects toward Earth’s centre. Explain that today they will discover how the same force keeps planets in orbit, and they will be able to predict orbital speeds.

1. Do‑now (5'): Quick quiz on Earth’s gravity and direction of “down”.
2. Mini‑lecture (10'): Introduce Newton’s law of universal gravitation and centripetal force; derive the orbital condition.
3. Guided practice (12'): Solve the Earth orbital‑speed example step‑by‑step on the board.
4. Interactive simulation (8'): Students explore how changing orbital radius affects speed and period.
5. Misconception check (5'): Discuss and refute the ideas “gravity only works on Earth” and “orbit needs a continuous push”.
6. Exit ticket (5'): Three short questions – formula recall, conceptual explanation, and a quick calculation.

Summarise that the Sun’s gravitational pull provides exactly the centripetal force needed for planetary orbits, linking the formula to real‑world values. Collect the exit tickets to gauge understanding, and assign homework to complete the worksheet’s remaining orbital‑speed problems.