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10 surprisingly easy sources of alternative energy

By: Bryan Nelson on Nov. 30, 2009, 11:27 a.m.
People walk on black asphalt tiles during early morning exercises.

Photo: Bignai/Shutterstock

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As the world's human population approaches a whopping 7 billion, tapping into the kinetic energy of human movement could become a source of real power. Piezoelectricity is the ability of some materials to generate an electric field in response to applied mechanical stress. By placing tiles made of piezoelectric material along busy walking paths or even in the soles of our shoes, electricity could be generated with every step we take — making people into walking power plants.