The other night, Joshua Foer posed this question was posed to a table full of science journalists. Most of us started talking about friction, and/or possibly something to do with the little flanges on either side of a train wheel.
We were all wrong.
This is a Richard Feynman video, yes, but it's more about mechanics than physics. Turns out, you can learn a lot about how trains stay on the track by looking under your own car.
The talk itself is great and covers some important stuff. (Of course, it's Feynman!) The key thing here is the connection between theoretical understandings of how the universe works and practical observations. Theories are used to make predictions. When the predictions turn out to be correct, we get some more evidence that the theory is on the right track. Here, Feynman talks about how the theory of gravity led to the discovery of the speed of light, and how knowledge of the effect of gravity on planetary orbits led to the discovery of the planet Neptune. Very cool stuff.
But what stood out to me—and what makes this different from all the old!Feynman videos I've seen—is the persona his younger self projects. Born and raised in Queens, the young Feynman comes across, at least in accent and physical mannerisms, like some big mafia palooka straight out of central casting. Most likely, my startled reaction to this is due to Midwestern bias and being raised in an era where American regional differences in accent and culture have been largely flattened out. But it's still fascinating ... and amusing as hell to hear a guy who looks and sounds like he should be guarding hostages or threatening shop owners instead talking about gravitational theory.