Day 52: Newton’s 3rd Law Demos


Today I led the classes in a series of Newton’s 3rd Law demonstrations. We learned the above demonstration from Eric Gettrust, our Modeling Instruction leader, which he published in The Physics Teacher. The purpose of this demo is to model the interaction between a person and the Earth, showing that the attraction force itself is equal though there is a greater effect on the smaller object. Close up below.


I also do car crashes (picture below), tug of war with two force detectors, and the class favorite, chest bumps with force plates.





6 Comments on “Day 52: Newton’s 3rd Law Demos”

  1. Andy "SuperFly" Rundquist says:

    These are great! Do you have the student brainstorm other things to try? I would imagine most of these were things you suggested, but I wonder what they’d like to try out. Or maybe I’m wrong and these already are their ideas.

    • The first one I do is the tug of war with two detectors, and after playing with that a bit I had them brainstorm. They usually came up with doing it vertically as well, so we try that, then did a bungee jump (sampling has to be at least 100 samples/s if using string), and since this year they are the wireless detectors, I even swung them in a circle!

  2. I also want to give props to my colleague Ben who set this up; I probably wouldn’t had done it if he didn’t try it first.

  3. bradwysocki says:

    Is that a large magnet that is attracting the paper clip from below? Do you have to zero the force sensor when the object is hanging there so that it doesn’t register the force of gravity? As you can tell I never read the article. Thanks.

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