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Potential Energy

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Posted by karela on June 5, 2009, 9:00 am
When we go upstairs we spend a lot of energy that gets stored as potential
energy. When we go downstairs we waste all the potential energy. Couldn't
anyone invent a good way of coming down so the potential energy could be
converted to other forms of energy that could be converted to electricity
when needed??

Posted by Jasen Betts on June 5, 2009, 8:36 am

an escalator driving a generator ?
piezo-electric stair treads?

Posted by Doc O'Leary on June 5, 2009, 3:36 pm

How much are you willing to spend on a contraption to power a 100W light
bulb for less than 1 minute?

<http://www23.wolframalpha.com/input/?i 0W+*+1+minute>

My personal UDP list:, localhost, googlegroups.com, ono.com,
    and probably your server, too.

Posted by daestrom on June 5, 2009, 3:49 pm

Well in *theory*, yes you certainly could.  Something as simple as a bucket
and rope tied to a pulley turning a shaft.  When you want to go downstairs
you just climb into the bucket and let it lower you through a hole in the
floor.  Of course there will be *some* losses.

But lets look at just how much energy we're talking about.  Raising a 200
lbm man up 10 feet in normal gravity would put 2000 ft-lbf of energy into
the man.  If you could recover *all* of that, that is a mere 0.75 watt-hours
(not kW-hr, just watt-hour).  So if he goes up the stairs 20 times a day for
a year, he'll have used 20*365*.75 / 1000 = 5.5 kW-hr of energy.  Recover
*all* of that perfectly and you have about $ worth of electricity for the

Going up stairs 20 times a day is great exercise, but it won't generate much
energy for you.


Posted by Charles on June 6, 2009, 12:34 am

Jump onto a platform with pulleys and counter-weights.  The resulting
rotational energy can be stored in a battery via a rotating generator.  The
overall efficiency will be less than 15%.  The time to pay of your
investment (for all of the pulleys, and gears, and a safe platform, and the
rotating generator with a storage battery) will be infinity years.

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