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Torque Converted to Electricity

  1. Nov 20, 2009 #1
    Request regarding my thread "Energy Converted to Electricity"
    I seem to have asked the wrong question; and would like to restate my problem in different format but still seeking a conclusion that I can use.

    Torque Converted to Electricity
    A piston moves horizontally [at a constant speed] for
    a distance of 9 feet every six hours. Then it immediately reverses its course and moves in the opposite direction at the same speed for the same distance and time. It repeats this travel every day, without interruption. Every day [24 hours] it makes four trips, each trip covering a distance of nine feet. At all times the WORK [energy] pushing the piston is 27,100 Tons.

    A metal strip is attached to the side of piston. The metal strip is exposed and lies horizontally from the top end of the piston to the bottom end of the piston; and is exactly equal in length to the piston. Thus, the metal strip rides piggyback [on the side] along with the piston on all of its travels. The exposed side [lateral side] of the piston contains cogs; with the cog teeth protruding toward and interacting with a cogwheel.

    The initial cogwheel is very large in diameter, but is then geared down to smaller cog wheels until the final wheel is spinning at a high rate of speed and turning the axel of an electrical generator.

    Is it possible to make even a wild guess as to how much electricity could be manufactured from such a contraption?
    Last edited: Nov 20, 2009
  2. jcsd
  3. Nov 20, 2009 #2
    I suppose you mean: the force pushing the piston is the same as a weight of 27100 tons.

    The energy in one trip of the piston = force * distance traveled = 27100*1000*9.81 N * 2.74m = 7.28 * 10^8 J The power required = energy / time = 7.28 * 10^8 J / 21600 seconds = 33703 Watt = 33.7 Kw.

    That is the maximum power. Losses when generating energy will be 10-20 % and there are also the losses from friction in the cogwheels.

    This would make an incredibly expensive generator, since it has to deal with such large forces, and delivers only as much power as a small car engine.
  4. Nov 20, 2009 #3


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    Staff: Mentor

    Please start forcing yourself to use the right terms. A ton is force, not work or energy (or pressure as you said in your other thread!).
    Absolutely! You haven't changed anything relevant to the energy calculation so the calculated energy is the same as it was before! Same force, same distance, same time.

    willem2 got a slightly different answer probably due to different conversion factors (I haven't checked the math...). [edit] Found it - willem2, since the distance is given in feet, you should probably assume those are English tons, not metric tons!
    You seem to think you can increase the output of a generator by gearing it to spin faster. You can't. As you gear it up, you decrease the torque applied exactly proportionally. This is a form of mechanical advantage: http://en.wikipedia.org/wiki/Mechanical_advantage
    Last edited: Nov 20, 2009
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