Newton’s 3rd Law (or How to Make Effective Use of Video for Instruction)

Exhibit A:

Exhibit B:
Download the high-quality video clips for each collision.


16 responses to “Newton’s 3rd Law (or How to Make Effective Use of Video for Instruction)

  1. Exhibit A: I did not finish watching the video

    Exhibit B: If the’ve done hooke’s law from the modelling approach then they can look at the spring compression from the video to verify equal forces and deduce that they are observing equal forces. this is fantastic!

  2. TL:DV (Too long; didn’t view).

    Nine minutes is more than I’m willing to spend on an undescribed video.
    The second video looks good. Have you tried using tracker to compute momentum before and after collisions?

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  4. There is a newer version of the first video…

    • I have never liked the rocket as an application of N3L. In student mode, I ask “How does the rocket push the gases backward? There is no plunger or piston forcing the gas out.”

      N2L makes a much stronger connnection, imho. The gases are pushing outward on the walls of the tank. There is no wall at the nozzle to push against, so there is no backward push by the gases on the tank. Thus, there is a net forward push on the rocket, and it accelerates.

      • Ugh, in the new Khan Academy video, the speaker makes it seem as if the force of gravity and the normal force form an action-reaction pair. That’s definitely giving students the wrong idea.

  5. Would love to do some video analysis with my class on the 2nd video. We did video analysis of free fall and they loved it and really got a better understanding of it.

  6. For the second video, don’t you also have to introduce momentum and elastic/inelastic collisions at the same time you are discussing the third law?

    • You can, but you don’t have to. All the students need to believe is that the deflection/bending of the hoop is a reliable indicator of the strength of the push that hoop either gives or receives. I let the kids define which it is. Their eyes tell them that each cart/hoop gives/receives the same push on/from the other. You can extend that to momentum transfer, or just leave it at N3L.

  7. The link to the high-quality videos seems to be broken today, which is too bad, since I wanted to try analyzing one to test some recent changes to Tracker (I’m trying to fix the velocity and acceleration computations to handle collisions better).

  8. Did this with my class today… Brilliant!

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  11. What we do with the kids in 6th grade is have them create their own videos to demo each of the laws. They are given a large selection of materials like scooters, “frictionless” cars, balls ranging from basketball to superball, whatever they can think of to use. We spend our time observing what happens with demos before they learn what the laws are…then they try to match the laws with what they have seen…then they make their own demo movie and share it. Admittedly it is at a 6th grade level but their understanding ends up pretty darn good. I love taking the time to let the kids observers, then give them the vocab and framework, then let them find a way to show us what they know.


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