>>I grew up about 100m from a railway. We had small coins of quite a soft alloy at the time, so we'd place one of them on the track and let a whole freight train drive over it. It would become gradually flattened into not exactly an ellipsis, but more of a circle which traveled about one or two of its diameters, depending on the length and weight of the train.
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>>IOW, poor hardware :)
>
>Yes, I was thinking of that because I'd heard of it here, too. I always wondered why the coin didn't fall off the rail from the vibrations.

Maybe because the vibrations are vertical, and the coin has too good a ratio of surface against height.