Lesson Plan: Buoyant Force Physics

This lesson plan includes the objectives, prerequisites, and exclusions of the lesson teaching students how to compare an object’s weight to the weight of the fluid displaced by the object and explain how this determines an object’s buoyancy.


Students will be able to

  • recognize that a submerged object displaces a volume of fluid equal to the volume of the submerged part of the object,
  • recognize that fluid pressure acts on all the submerged surfaces of a submerged object,
  • show that the difference between the fluid pressures on the top of and on the base of a submerged object results in a vertically upward force on the object (called upthrust),
  • determine the buoyancy condition for an object by comparing the weight of the object to the upthrust on the object,
  • use the formula buoyant force = fluid mass displaced × acceleration due to gravity.


Students should already be familiar with

  • the formula density = mass per unit volume,
  • the formula pressure = force per unit area,
  • the formula pressure within a fluid = fluid density × acceleration due to gravity × fluid depth.


Students will not cover

  • atmospheric pressure.

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