Science

So long as they don't butcher the runts for scrapple.

Two MIT grad students in the architecture program have an idea to harness the energy of moving crowds using blocks under the floor that depress and rub against one another when stepped upon, generating electricity. The concept, which they call a Crowd Farm, would work best in a place like a train station, where you have a lot of people moving all the time. According to this article, while one step can power a single lightbulb for one second, 28,527 steps could power a train for one second.

Which, you know, won’t really get you very far but whatever.

As a test case, the guys built a chair that lights up when you sit down. Great for reading, not so much for relaxing but again, whatever. Very cool!

What will those crazy MIT kids think of next? Place your guesses in the comments.

Rebecca Watson

Rebecca leads a team of skeptical female activists at Skepchick.org. She travels around the world delivering entertaining talks on science, atheism, feminism, and skepticism. There is currently an asteroid orbiting the sun with her name on it. You can follow her every fascinating move on Twitter or on Google+.

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22 Comments

  1. Harness the power of incoming wind in speeding cars to ZAP the driver when he tries to talk on the cell phone.

    Computer keyboards, phone keypads, all sorts of game controllers…

    Really, really cool. There's so much energy around that I wonder why we have been so obsessed with oil.

  2. Chupacabras said:

    There’s so much energy around that I wonder why we have been so obsessed with oil.

    Simple. It's a lot harder to sell you the energy of your own motion.

  3. We dont generate much power as people really. While collectively it sounds like a lot, the average power we create compared to how much we use, means any mechanical energy will only be a tiny proportion.

    Theres lots of reasons why we arent letting go of oil too easily without having to get cynical . Its easy to get, energy dense, easily transported, etc etc. Making something like the above work reliably will be pretty hard work by comparison.

    Otara

  4. WP and Otara,

    Lest we forget the oil engine base, which provides comfort and way of life. I only wish there was more progress in any form of alternative energy. I have the feeling that ethanol is going to bring more social troubles than benefit.

  5. Hmm…

    treadmill/stair stepper

    an automotive version for tollbooths, tunnels, and drawbridges

    anywhere there’s a relatively slow moving line, rides at amusement parks, airport check in, the national archives, every mall in America

    Ranches and cattle farms, anywhere animals move across the same ground frequently.

    The drive through at dunkies

  6. Would it be more tiring to walk on such a floor, like damp soil as opposed to concrete? They're basically taking the spring out of your step and converting it to electricity, are they not?

  7. wb4: Yes, as all of the energy comes from your weight depressing the block, on the next step you would use slightly more energy taking the next step as you have to lift the body a small amount to the next block which, not being depressed, is sightly higher than the depressed block. How much more energy is required compared to walking on a level surface, i.e. how tiring it would be, depends on the amount each block depresses and of course how far you were to walk on it.

  8. Yes they are stealing the spring in your step but that just means they can sell it as environmentally friendly and a way for people to get the extra exercise we all know we should be getting.

    And the more over-weight you are the more energy you need to add to haul yourself up to that non-depressed block. Perfect.

  9. What may be more tiring to walk on from an energy point of view, is probably healthier for your knees, ankles and hips, since the floor tiles take away some of the impact of putting your weight on one foot. They would effectively act as a shock absorber and reduce the stress on your joints.

    This impact is no doubt what's producing the power they're harvesting, not the push-off towards the next tile.

    Essentially, the kinetic energy that's normally wasted reverberating through your bones and joints, is now being collected by the floor.

  10. The only thing I'd be worried about (especially one a train platform) is tripping on the block in front of you. Not to mention, in a crowd, all blocks would be pushed in constantly – thus, they would never really come up and go down… unless they are small blocks, like 1" tiles. That might make more sense.

    I like the idea, and years ago I was using my mom's manual treadmill, the kind that put up very little resistance but don't use electricity, and I thought, "What if we could use this to power something…"

    This country is fat, and expensive. Maybe we should start requiring a certain amount of exercise each day, on a machine that takes that energy and converts it into electricity. Then, we'd alleviate both problems at once! Huzzah!

  11. I doubt they're talking about a standard (60 Watt) light bulb. I take about 2 steps per second, which they say should light TWO bulbs continuously as I walk… but you should try setting a treadmill or stair-stepper to the equivalent of 120 Watts. (Some have digital readouts in Watts.) It's HARD!

    Personally, I would avoid walking across any surface that added that much effort to my going across.

  12. Amanda, I don't know if the tiles are actually moving up and down that much? Actially, they're merely converting force to electricity, not motion, so they might not even have to move at all.

  13. Exarch, you have an even better point than the one I was going to make but oh well. If the tiles do need to go up and down I think small tiles or a heavy rubber-style surface that ripples a little rather than moving in separate pieces would work.

    So it would be like walking on something slightly soft but not enough to make you trip.

    I really like the required excercise idea Amanda! I would add that it should be "means-tested" so the fattest people would do the most required exercise. This would mean I had to do more exercise but that is probably a positive…

  14. It would be so much easier if we could just tap straight into the human body and use the electricty there. Of course, we'd have to put those minds somewhere so they don't cause trouble…

  15. thad, I think someone actually mentioned this in a show or an interview somewhere in response to "The Matrix", but the human body really doesn't produce all that much energy.

    It wouldn't surprise me if you were able to generate more electricity from just burning food in a fire than in having a human digest it and turning it into nerve impulses.

    Very energy-inefficient we are.

    I've heard there are bacteria that do much better than we do. Now there's a thought …

  16. >>"Actually, they’re merely converting force to electricity, not motion, so they might not even have to move at all."

    You can't convert force to electricity without some motion.
    Energy = force*distance.
    If force =~bodyweight, distance = negligible, energy absorbed =negligible.

    (The human body already damps footfalls to give peak forces of the order of bodyweight when walking, and there's no obvious external way to increase the force.)

  17. I don't think your force is ~bodyweight. I think the force is the actual impact of your step, which is bodyweight * speed-of-impact.

    Obviously, you need some motion to transfer force to energy, but you don't need a lot of movement.
    I think the formula you're using is one that works well with levers. For example, the smaller the distance to the pivot point, the bigger the force needed to achieve the same amount of "work" compared to a really long lever. But this formula says nothing about the amount of electric energy you can extract. It's simply a different kind of "energy".

  18. If anything, I'd expect it to be more of a compressive motion, a la piezoelectrics, than like putting a bunch of people on giant hamster wheels or whatever. So gravity is actually going to be doing more of the work than the people will; the people are responsible for the recovery stroke of raising their feet to take the next step, rather than the actual power stroke that generates the electricity.

  19. >>"I don’t think your force is ~bodyweight. I think the force is the actual impact of your step, which is bodyweight * speed-of-impact."

    When walking, at the point of 'impact', much of the bodyweight is supported by the rear leg. Even if the landing foot has some vertical speed, the mass one might use to calculate an impact presumably isn't the body's mass, but some fraction of the mass of the foot-limb system, and much of the time, the impact speed is really not great.

    Looking for ground reaction force data to back up my assumptions, it seems there is an initial 'spike' of force, but that initial spike is rather less than bodyweight, and really isn't much more than noise imposed on a gradual buildup of force – the overall shape of the ground reaction force graph for normal human walking seems to be essentially a slow rise to a peak, a gentle decline and then a second peak before slowly dropping to zero. The peaks only seem to be of the order of 125% bodyweight.
    Graphs at:
    http://www.staffs.ac.uk/isb-fw/ISBFootwear.Abstrahttp://www.univie.ac.at/cga/faq/grfs.html

    If a device people step onto does drop slightly in order to extract energy, the work is done not so much by people raising their feet for the next step, but by continually trying to take a step up to a slightly higher ground level which then sinks slightly under their weight – muscular effort trying to lift their whole body up (and/or pushing the next device down to their slightly lower level, depending on one's perspective).

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