There is a very good video from 1937 by Jam Handy. It explains why we need differential gears and how they work.

I think the video is a masterpiece of an explanation. I recommend you watch it, not because understanding differentials is essential (though that doesn't hurt), but because the video can teach you a lot about how to explain something properly.

Here are some techniques the video uses (non-exhaustive):

  • Start with giving the context of why the thing that is being explained is important, e.g. by describing a concrete problem to which the thing to be explained is the solution.
  • Use visual explanations. Specifically, demonstrate the mechanism to be explained in action.
  • Start to explain a simple toy model and then add layers of complexity until you arrive at the real deal.

I think I have never seen an explanation, that by its end has annihilated the possibility of misunderstanding so effectively, and I really like how smooth the transition is from background story to technical explanation. There is no jarring break.

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4 comments, sorted by Click to highlight new comments since: Today at 12:56 AM

That was a great video! Thanks for sharing it.

Worth pointing out:

  1. While the video seems like a hidden gem, and I certainly didn't know it, it turns out that this version with worse resolution (240p vs. 480p) has 21 million views.
  2. The same channel ("US Auto Industry") as the 21-million-view video above, shares this Vintage "How Cars Work" Films playlist which contains 10 other videos from 1936-1956. I haven't checked any of the other videos myself, so I don't know if they're as good or as timeless as the one on differential gears. But they're sorted by view count, and e.g. the second one on Spinning Levers still has 10 million views. (Caveat: With Youtube versions of old famous films, you can never be sure whether the version with the most views is the one with the best resolution. So if a video has an unwatchably low resolution, it sometimes pays off to search for versions with better resolution.)
  3. And on the same channel, there's a bigger playlist called How Cars Work and Stuff Like that, containing 22 videos but with much overlap to the first playlist.

EDIT: And if someone really wanted to dig into the Jam Handy archives, a ton of their films are available on the Internet Archive. Realistically speaking, though, most of them probably aren't very good or relevant.

Yeah, I've seen this video before. Still excellent.

That video was so goood I forgot to pay attention to what techniques it used. Strong upvoted. 

This was great.

Tangentially, this post reminded me of this GPS explainer which I also thought was excellent as explanation.