How trains stay on the tracks

You have to hand it to Richard Feynman. He had a way of not only making difficult physics concepts understandable, he could also make everyday phenomena interesting by posing and then answering questions that do not even occur to most of us or, if they do, to which we are likely to give a facile or wrong answer.

Maggie Koerth-Baker brings to my attention a video in which Feynman explains how it is that trains stay on their tracks. It was new to me and quite fascinating. Although when I taught mechanics I had explained about the need for a differential on the wheel axes of cars to enable them to make turns, I had never wondered as to why train wheel axles did not have them.

Now I know.


  1. Rob Grigjanis says

    Two people I could listen to anytime, talking about anything, are Feynman and Leonard Susskind (maybe I just like New York accents). So here is Susskind talking at a tribute to Feynman. There’s even some physics in the last five minutes or so.

  2. machintelligence says

    He doesn’t mention that the rails are crowned as well. Also on the cars (and on modern locomotives) the wheels are mounted on trucks which turn on a center pivot which minimizes the differential effect. The old steam locomotives, especially the 4-8-4 configuration with 4 drive axles squealed on tight radius turns. If you ever see a rail grinding rig recrowning track it is most impressive. It uses huge grindstones, perhaps 8 feet in diameter, and the smoke and sparks, especially at night, are something to behold.

  3. Francisco Bacopa says

    The entire “Fun to Imagine” series is a joy to watch. And as always with Feynman videos, his deep passions shaped by his guilt over working on the atomic bomb after his original reasons for wanting to do so no longer were the case, his grief over the death of his first wife, and his descent into and recovery from a period of alcoholism shine through in this series.

    I would recommend that everyone go watch “The Pleasure of Finding things Out” on youtube.

  4. M, Supreme Anarch of the Queer Illuminati says

    Feynman, in every video of him that I’ve seen (and in prose aimed at general audiences), just seemed to radiate utter delight at the experience of learning and discovery. He’s certainly not the only one with that experience (see, e.g., most people who are deeply involved with science), but from him it’s just infectious.

  5. Marshall says

    Feynman was obsessed with learning how everything worked, down to the smallest detail, and it’s incredibly obvious in his interviews. It’s incredibly infectious!

  6. kyoseki says

    That’s awesome, it had never occurred to me that trains corner in a similar fashion to motorcycles.

  7. Acolyte of Sagan says

    And there was I thinking they stayed on by magic! Pesky science and scienticians, always shattering delusions :-))

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