Lesson Plan: Triangle of Forces Mathematics

This lesson plan includes the objectives, prerequisites, and exclusions of the lesson teaching students how to solve problems about the equilibrium of a particle under the action of three forces meeting at a point using the resultant of forces or triangle of force method.


Students will be able to

  • find a missing force in a system in equilibrium using the triangle of forces rule,
  • understand the conditions for equilibrium under two forces,
  • understand the conditions for equilibrium under three coplanar forces meeting at a point and apply this to examples.


Students should already be familiar with

  • the Pythagorean theorem,
  • forces given in terms of unit vectors, given in polar form, and represented graphically,
  • the magnitude and direction of forces,
  • adding and subtracting forces,
  • equilibrium.


Students will not cover

  • Lami’s rule,
  • systems that are not in equilibrium.

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