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I tutor some high school students, mostly in math but occasionally in Physics as well; I love the science but only took it through the high school level plus a couple of first-year university courses. I've noticed that nowadays almost all texts use the concept of a lever arm when introducing the idea of torque. This was an idea that I only ran across when I started tutoring; when I learned about torque in high school (I can't remember whether it was part of my university courses), we were simply taught to use the component of the force perpendicular to the moment arm, an idea that immediately made sense to me. I understand that computationally the two approaches are equivalent, but it seems to me (as a non-Physicist at least) that the use of a lever arm is a much less intuitive approach than the way I was taught. I would love to get some idea of why this approach is now preferred.

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  • $\begingroup$ What is this lever arm concept? can you give a reference where you saw this? $\endgroup$
    – Babu
    Oct 7, 2020 at 6:40
  • $\begingroup$ This is a tad opinion-based question. I personally find the moment arm approach more intuitive and easier to visualise. Thus I don't know if there is a definitive answer to this question other than: "The authors liked the lever arm approach and thus all others followed the same." $\endgroup$
    – FakeMod
    Oct 7, 2020 at 7:44
  • $\begingroup$ @Buraian here's just one example: hyperphysics.phy-astr.gsu.edu/hbase/torq2.html ; scroll down to the bottom half of the page. $\endgroup$
    – A.J.
    Oct 7, 2020 at 11:08
  • $\begingroup$ @FakeMod My apologies for injecting some opinion into the question, I wasn't aware that was bad form. However I asked the question to see whether there were some objective advantages to the use of lever arms that I might be overlooking.. $\endgroup$
    – A.J.
    Oct 7, 2020 at 11:16
  • $\begingroup$ Maybe one advantage is that if you draw the lever arm on a picture, you can immediately see by the length of the lever arm if the torque will be "large" or "small" (for a given applied force), as opposed to needing to do an extra mental step of dropping a perpendicular. $\endgroup$
    – Andrew
    Oct 7, 2020 at 14:51

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