What ideas do students have about Newton's third law?

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Episode 109: Scratched University of Maryland

Research suggests that students have both productive ideas about and difficulties with Newton’s laws, and Newton’s third law is notoriously counterintuitive for students. What ideas do students have about Newton’s third law?

July 2, 2018

Pedagogy Content
Attending to student ideas
Physics Content
Newton's laws
Instructor Interaction

Lesson Contents (2 MB)Student Handout
Transcript, discussion questions, and problem

(1 MB)Specific Lesson Guide
Facilitator's guide for this lesson

(1 MB)General Facilitator's Guide
Background and best practices

(126 MB)Video
Captioned video


Sample Discussion Prompts

  1. What did you notice in this episode? Talk to your neighbor about what you noticed.

  2. Claudia says, “I don’t think there’s any way you can explain to me how a massive truck is going to have the same forces on it.” She has probably heard explanations before. Why do you think she says this can’t be explained to her?

  3. Delia says, “I think they do feel the same force… it just looks like that one got the push” (lines 18-20). What is your understanding of her point?

  4. Alan says that the Porsche would be significantly damaged (“totaled,” line 25) while the truck would have damage to the fender (line 27). What is your understanding of his point?

  5. Claudia reacts with seeming incredulity to Alan’s suggestion that the truck would not suffer much damage (“Scratched?”, line 28). What point does she seem to be making?

  6. What does this episode suggest about what ideas students have about Newton’s third law?

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