Lesson Plan

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Lesson Plan
Grade: Date: 25/02/2026
Subject: Physics
Lesson Topic: derive, from Newton’s law of gravitation and the definition of gravitational field, the equation g = GM / r 2 for the gravitational field strength due to a point mass
Learning Objective/s:
  • Describe Newton’s law of universal gravitation and the concept of a gravitational field.
  • Derive the expression g = GM/r² from the law and the field definition.
  • Apply the derived formula to calculate field strength for Earth and other point masses.
  • Explain the radial direction and sign conventions of the gravitational field.
  • Identify common misconceptions about gravity’s constancy and direction.
Materials Needed:
  • Projector or interactive whiteboard
  • Whiteboard and markers
  • Printed worksheet with derivation steps and example problem
  • Scientific calculator
  • Student notebooks
  • Optional: simulation software (e.g., PhET Gravity)
 Introduction:
Begin with a quick demonstration: drop a ball and ask students why it accelerates. Recall the previous lesson on forces and the definition of a field. Today’s success criteria: students will correctly derive g = GM/r² and use it in a calculation.
Lesson Structure:
  1. Do‑now (5’) – Students solve a short problem on force per unit mass; teacher checks answers.
  2. Mini‑lecture (10’) – Review Newton’s law and introduce the gravitational field definition, using the board.
  3. Guided derivation (15’) – Work through the four‑step algebraic derivation together, prompting students to fill blanks on the worksheet.
  4. Application activity (10’) – Small groups calculate g at Earth’s surface and at a satellite altitude, then discuss results.
  5. Misconception check (5’) – Quick quiz (Kahoot/hand raise) on direction of g and variability with distance; teacher provides feedback.
Conclusion:
Summarise that g = GM/r² follows directly from Newton’s law and shows how gravity weakens with distance. For exit, each student writes one real‑world example where the formula is useful. Homework: complete the worksheet with an extra problem involving the Moon’s gravitational field.