[dorkbotsea-blabber] Electricity and human power

[rich at spambutcher.com]

Having problems finding good sources -

http://www.physicsforums.com/archive/index.php/t-58140.html

"A good cyclist could generate .4 horsepower indefinitely"

that would be something around 300 watts - or a good chunk of your bank 
of lightbulbs.

gotta think somethings probably not quite right with your math...

(might have something to do with calories as typically used is actually 
kilocalories. we don't use 2000 calories / day - we use 2 million!)

-Rich

Seth! Leary wrote:
> 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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