Good old gravity. It’s always there for us, keeping us grounded — and now, charging our electric trains indefinitely. A mining company in Australia recently explained that four of its electric trains create so much electricity through regenerative braking going downhill, they can power themselves back to the top of the hill, and have a little extra battery power left over. Science!

So, of course, there’s a tiny catch: It’s the added weight of the cargo going downhill that helps to create so much energy through braking. When the vehicle goes back uphill, it’s significantly lighter, because it’s empty. There’s no such thing as free energy, and the laws of physics are unbending. Still, the net result is an electric vehicle that basically powers itself throughout its duty cycle. Neat!

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