Have you ever considered the irony of a gym full of people using electrically powered exercise machines to burn energy? What if the mechanical energy of those moving bodies could be converted into usable electric energy? That’s exactly what Arthur Kuo, a University of Michigan mechanical engineer, and his colleagues have done. Both News in Science and Science Friday focused on this story Friday, February 8, 2008.

The News in Science story, Knee Gadget Fires Up Your Mobile by Will Dunham, reports the device works like the electricity generators in hybrid automobiles, harnessing the heat normally dissipated from moving engine parts when the car idles. The knee gadget harnesses such heat during the phase when the foot is at the back of the stride coming away from the ground and moving forward to take another step with the help of knee flexor muscles. The video posted with the Science Friday story Harvesting Energy From Walking illustrates this nicely in slow motion segments. Color labels identify the key events in the process.

The device can power up to 10 mobile phones at a time, or other such small devices. However, due to its weight, 1.6 kilograms, or about 3 pounds, and its bulk, it’s not ready for the mass market yet. Both news sources report this is not the first device made to convert mechanical energy of the human body into electric energy, but it is the most promising thus far. Both stories show photos of the device on a knee.

How to Turn This News Event into an Inquiry-Based, Standards-Related Science Lesson

This story does triple duty in aligning with the National Science Education Standards of Physical Science, Life Science, and Science and Technology. It’s all about force and motion and energy transfer, as well as structure and function in living systems, and of course, abilities of technological design. You can start your discussion of this device and its related science concepts with the question posed at the start of this article. Lead students to articulate, review, and reinforce the notions of energy conversion and transfer in keeping with the law of conservation of energy. This provides a firm ground upon which the scientists hypothesize and predict. That is, the notion of the human body as a source of electrical energy is perfectly tenable due to the first law of thermodynamics.

Ask students, What is the by-product of all energy conversions? Can heat energy be converted to electric energy? How do you know? Have students read the Science Friday article and show them the video. Be prepared to replay the video a few times, in order to afford the students ample opportunity to process what it illustrates.

Here are some additional resources that are part of the NSDL Middle School Portalcollection to facilitate your instruction regarding energy sources and conversions: Energy Transfers; Quick Take on The Power of Electricity; and Quick Take on Energy Sources.

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