[dorkbotsea-blabber] Electricity and human power

Seth! Leary email at sethleary.com
Tue Jul 29 17:45:52 EDT 2008


Hi brilliant minds,
 
I have a question for you. I suppose that you have seen the pedal-power
exhibit at the Pacific Science Center. You pedal the bike and the
faster/harder you pedal, the more lights illuminate. The idea is to show how
many calories you could burn in an hour at that rate. The bulbs are sort of
incidental. I contend that there is some kind of trick involved but my
friend thinks that the pedaling is actualy lighting the bulbs via a
generator.
 
His theory seems wrong to me. You have to pedal like mad to get a headlight
on a bike generator to light up. That's maybe a 5 watt bulb, right? How can
the same mechanism (albeit with a possibly larger rotor) illuminate a whole
bank of 60 watt bulbs? I think that a person would burn about 600 calories
per light bulb to keep it going for ten seconds, if no energy were lost to
friction. That's a third of the normal daily energy of a person--for one
bulb for ten seconds! A bank of bulbs would burn days' worth of calories in
a matter of seconds. That is, if my calculations are correct. Looking at it
from the reverse angle, I think that pedaling the bike for ten seconds burns
less than two calories. How can two calories light up a bunch of bulbs? If
that were possible, we could put electrical turbines on streams instead of
huge dams.
 
Something is fishy. Who is right? Am I completely wrong in my thinking...or
math?
 
- Seth!
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