[dorkbotsea-blabber] Electricity and human power
rich at spambutcher.com
rich at spambutcher.com
Tue Jul 29 19:45:14 EDT 2008
Watt to Calorie / Hour converter:
So if the light bulb array is 600 watts - it would take 515907 calories
or 515 "food" calories to keep it lit for one hour.
(conveniently close to 1 food calorie = 1 watt/hour for guesstimates...)
I suspect it would actually take a more than that due to inefficiencies
in the human / bike / generator, etc.
Kevin Purcell wrote:
> Wrong kind of "calories"
> What people who do nutrition call a "calorie" is really a "large
> calorie" or a "kilogram calorie" what an (old) scientist would call a
> kilocalorie (a thousand small calories).
> I leave out the bit about calories at different temperatures (as it
> doesn't make a difference here) but you can get all the details in
> When they start labeling our food in kiloJoules when know we've got
> somewhere with science education.
> Onto the other half of the question ... rather than just make stuff up
> I'll use stuff that's already been made up at Wikipedia ...
>> A human being traveling on a bicycle at low to medium speeds of around
>> 10-15 mph (16-24 km/h), using only the power required to walk, is the
>> most energy-efficient means of transport generally available. Air
>> drag, which increases roughly with the square of speed, requires
>> increasingly higher power outputs relative to speed. A bicycle in
>> which the rider lies in a supine position is referred to as a
>> recumbent bicycle or, if covered in an aerodynamic fairing to achieve
>> very low air drag, as a streamliner.
>> On firm, flat, ground, a 70 kg man requires about 100 watts to walk at
>> 5 km/h. That same man on a bicycle, on the same ground, with the same
>> power output, can average 25 km/h, so energy expenditure in terms of
>> kcal/kg/km is roughly one-fifth as much. Generally used figures are
>> * 1.62 kJ/(km∙kg) or 0.28 kcal/(mile∙lb) for cycling,
>> * 3.78 kJ/(km∙kg) or 0.653 kcal/(mile∙lb) for walking/running,
>> * 16.96 kJ/(km∙kg) or 2.93 kcal/(mile∙lb) for swimming.
>> The average "in-shape" person can produce about 3 watts/kg for more
>> than an hour (e.g., around 200 watts for a 70 kg rider), with top
>> amateurs producing 5 watts/kg and elite athletes achieving 6 watts/kg
>> for similar lengths of time. Elite track sprinters are able to attain
>> an instantaneous maximum output of around 2,000 watts, or in excess of
>> 25 watts/kg; elite road cyclists may produce 1,600 to 1,700 watts as
>> an instantaneous maximum in their burst to the finish line at the end
>> of a five-hour long road race. Even at moderate speeds, most cycling
>> energy is spent in overcoming aerodynamic drag, which increases with
>> the square of speed; therefore, power needs increase approximately
>> with the cube of speed.
> So you can put out about 100W for a extended time period. So the
> headlight bulb is perhaps a bit larger than you think it is plus there
> are probably losses in the system.
> BTW, the resting energy of most humans in is the 80W to 100W range just
> to keep your body warm you use about 80% of your calorific intake for
> that. It's one of the resons that exercise seems to work to loose weight
> -- it increases you resting metabolism so the time your are not
> exercising you are burning off more calories than the amount you use
> during the vigorous exercise.
> Little known fact: When testing house insulation 75W to 100W bulbs are
> often used to simulate the heat output of a person living in the house.
> You can even get them to move around by switching lights on and off.
> On Jul 29, 2008, at 2:45 PM, Seth! Leary wrote:
>> His theory seems wrong to me. You have to pedal like mad to get a
>> 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
>> bank of 60 watt bulbs? I think that a person would burn about 600
>> 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!
> Kevin Purcell
> kevinpurcell at pobox.com
> .........dorkbot: people doing strange things with electricity..........
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