Lesson Plan

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Lesson Plan
Grade: Date: 01/12/2025
Subject: Physics
Lesson Topic: use a vector triangle to represent coplanar forces in equilibrium
Learning Objective/s:
  • Describe the equilibrium condition for coplanar forces (∑ F = 0).
  • Construct a vector (force) triangle to test whether a set of forces is in equilibrium.
  • Calculate the magnitude and direction of an unknown force using the vector‑triangle method.
  • Interpret a closed triangle as confirmation of equilibrium and an open triangle as indicating the resultant.
  • Apply the method to solve a typical A‑Level mechanics problem.
Materials Needed:
  • Whiteboard and markers
  • Projector with slides of vector‑triangle diagrams
  • Ruler and protractor for scale drawings
  • Graph paper
  • Scientific calculators
  • Worksheets containing a worked example and practice problems
 Introduction:

Begin with a quick visual puzzle: “Can you see how three forces can balance like the sides of a triangle?” Review students’ prior knowledge of resolving forces into components and the algebraic equilibrium condition. State that by the end of the lesson they will be able to represent any coplanar force system graphically and determine any missing force.
Lesson Structure:
  1. Do‑Now (5'): short quiz on ΣFₓ = 0 and ΣFᵧ = 0.
  2. Mini‑lecture (10'): recap vector components and introduce the vector‑triangle concept.
  3. Teacher demonstration (8'): draw a vector triangle for the three‑force example on the board, showing each step.
  4. Guided practice (12'): students work in pairs to construct the triangle for the given forces and calculate the unknown force, using rulers and calculators.
  5. Check for understanding (5'): pairs share results; teacher confirms closure of the triangle and discusses common errors.
  6. Independent practice (10'): worksheet with two additional problems of increasing difficulty.
  7. Summary & reflection (5'): recap the five‑step procedure and ask students to write one key takeaway on a sticky note.
Conclusion:

Review how the vector triangle provides a visual check of equilibrium and reinforces the algebraic method. Collect exit tickets where each student records the magnitude and direction of the unknown force for a new set of forces. Assign a homework task to complete three extra vector‑triangle problems from the textbook.