At a Glance


  • STEM
  • Physics

Instructional Level

  • College & CEGEP
  • University


  • Mechanics

Tasks in Workflow

Social Plane(s)

  • Individual
  • Group
  • Whole Class

Type of Tasks

  • Collecting & seeking information
  • Analyzing
  • Reviewing & assessing peers
  • Revising & improving
  • Reading

Technical Details

Useful Technologies

  • Interactive whiteboards

Class size

  • Small (20-49)
  • Medium (50-99)


  • Single class period (< 90 mins)

Instructional Purpose

  • Application & knowledge building
  • Assessment & knowledge refinement


In this activity, two problems which are similar but have an important difference are assigned to groups. In this case, both groups must find the force of friction between two blocks (one on top of the other) as well as the applied force. In one case, however, both blocks accelerate together, whereas in the second the upper block is tied to a wall behind them.

Each group works on their problem (at a whiteboard or SMART board). Before any group can finish, the instructor calls on the students to switch whiteboards or SMART boards with a group working on the other problem. Groups must identify the difference and determine how it will alter the way in which the problem must be approached. They then evaluate the other group’s work, correcting any errors, and complete the second problem.

Time permitting, the groups return to their original problem and determine whether or not they agree with the second group’s solution. After the problems have been completed, the instructor reviews the solutions, paying close attention to the differences between the two problems, to the errors which led to incorrect solutions, and to different approaches to each problem.


Instructional Objectives

  • Students will learn to apply Newton’s second and third laws to problems involving friction between multiple objects.
  • Students learn to identify key distinctions between similar problems.

Workflow & Materials


Activity Workflow

View on CourseFlow

Contributor's Notes

Jean-François Brière

Jean-François Brière

Dawson College, Montreal


This activity exposes students to variations of a typical problem in a shorter amount of time than it would take to cover both problems. Students are forced to analyze the work of other students in order to continue, and to contrast superficial details between the two problems. When the problems are side by side, students can easily see the difference between the two and how it affects the question.


Choosing problems at the right level is difficult, and choosing incorrectly can cause problems in pacing – students should advance at a similar pace. You need to choose problems that are hard enough that no group finishes it right away, but also not so hard that no groups finish the problem.


Try to avoid getting involved too early. Students will have questions, but you should allow them to struggle and make mistakes so that other groups can then catch these mistakes. If no errors are made, there is much less point to this activity.

Obviously you should ensure that no team is able to finish before you do the first rotation: keep careful track of how far your more “advanced” groups have gotten.

Other contributors to this activity:

Michael Dugdale (John Abbott College), Rhys Adams (Vanier College), Greg Mulcair (John Abbott College), Jonathon Sumner (Dawson College), Joel Trudeau (Dawson College)

Applied Strategies


  1. Wow, nice activity Jean François. I can’t wait to adapt it and try it out with my own discipline content.


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