I can't help myself. When I'm out in the real world and I see something cool, I have to turn it into a physics problem. It's just what I do. In this case, I was changing planes in the Atlanta airport. Like many other airports, Atlanta has a mini subway to take you between terminals. You walk in, the doors shut and then it accelerates up to some traveling speed. At some point it slows down and stops so that you can get off and catch your plane.

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