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Car Talk: Perpetual-motion plug-in becomes a possibility

Dear Car Talk: Lithium-ion batteries are now smaller and more efficient than ever. Would it be possible for a front-drive, fully electric car to use a generator where the differential normally would be on a rear-drive car, and have that generator be powerful enough to use the rear-wheel rotation to recharge the battery, giving us an electric car that needed no fuel or recharging at all? – Tony

Only if you added a main sail and a consistent, 50-mph tailwind, Tony.

What you’re proposing is called a perpetual motion machine.

Your fellow tinkerers and wackos have been trying to invent one since the Middle Ages.

But no machine can produce as much energy as it consumes from a finite source and run indefinitely.

The primary problem is that some energy always is lost to friction. You can reduce the losses to friction, but you can never eliminate them.

And on a theoretical level, the problem is that a perpetual-motion machine violates both the first and second laws of thermodynamics, which are fairly well-established.

But maybe a President Trump would simply cross out those two objectionable paragraphs, Tony, and then you’ll be all set.

Write if you figure it out. I’ll be ready to invest.

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