According to the laws of physics — at least in simplified form — an object in motion will stay in motion, at least if no other forces act on it. That’s all well and good in the realm of theory, but here in the complex reality of Earth, there always seems to be one force or another getting in the way. Not that this has ever completely shut down mankind’s desire to build a perpetual-motion machine. According to Google Arts & Culture, that quest dates at least as far back as seventh-century India, where “the mathematician Brahmagupta, who wanted to represent the cyclical and eternal motion of the heavens, designed an overbalanced wheel whose rotation was powered by the flow of mercury inside its hollow spokes.”

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