There was a time, years ago, when surface cars were slowed and stopped by friction, rudely applied. Then a bright lad realized that a turning wheel could be stopped by treating it as a generator and making it pay for the privilege of being stopped—the angular momentum could be extracted and stored in a “storage battery”
Quote from The Cat Who Walks Through Walls
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Early braking showed turning wheels could be treated as generators, using friction to harvest energy and store it in a storage battery.