Motion is energy. Capturing that energy is easy if you're talking about huge turbines. But what about tiny motions, like a footstep?

A number of new projects aim to use the energy of human activity and translate it into ways to power the portable devices we so love. The photo above is an obviously early prototype of one such device - a shoe that captures enough energy to power a portable music player.

This particular shoe-slash-power plant comes courtesy of NTT Docomo, a Japanese telecom. They hope to boost their prototype's output from 1.3 watts to 3 watts, which they say would be enough to keep your cell phone perpetually charged. NTT expects a commercial version of the shoe-generator in as little as two years.

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But walking is just so... passive. What about people who are even more active? What about dancers? Enter a company called Gotwind, which is working on a device it calls the Dance Charger. You strap the device to your arm and it converts the energy from your motions to electrical energy, which can then power a cell phone or anything else.

Both of these devices are in the concept phase, but you can be sure we'll see things like them on the market soon.