You know how sometimes there’s a neat science fiction technology that the writer uses to advance the story line, but upon further thought, you realize there are much better uses for that sort of technology? Example, time machines.
So how about this? A character in the story works out with a newfangled weight set. But it’s just a single bar with some buttons that adjusts the weight. So the character doesn’t need to fumble with heavy weight discs and doesn’t need a spotter.
But I’m sure a material that can control its apparent weight (say by a factor of 10) at the push of a button has much better practical applications. Would it result in perpetual motion and free energy? Can conservation of energy and conservation of mass be preserved?