An image of a rusted train in Uyuni, Bolivia. Nearby is one of the largest salt flats in the world. Many locals make their living harvesting the salt and selling it as a commodity. Old trains that used to transport the salt now sit in the desert sun, slowly rusting into oblivion. Someone wrote Netwon’s universal law of gravity, F= GMm/R², on this engine. I think the Boltzman’s equation relating to entropy would have been more appropriate.