<CSIRO Future Fuels ForumThe Oil DrumDrumBeat: January 28, 2008>

64 comments on Matt Simmons, a Sasquatch, and a Chimp in Texas Monthly and History Channel 'Doomer Porn' Day

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Ywish on January 28, 2008 - 1:49am Permalink | Subthread | Parent | Comments top

A reply to Nate Hagens

Read the post at http://www.theoildrum.com/node/3412

According to the first comment by shargash the calculation has a long pedigree.

I think either (or both of) Matt Savinar or Roscoe Bartlett used the 25,000 number in Crude Awakening. At least the first place I saw the number was the film.

If you quoted their figure, clearly it's not a misprint or a miscalculation on your part.

To the person/persons who carried out the original calculation:

The calculator at http://primusweb.com/fitnesspartner/jumpsite/calculat.htm calculates energy requirement for 222 different activities based on weight and duration.

The issue then revolves around what can be realistically defined as “hard human labor,” typing on a keyword, or doing forestry/ general work in a steel mill. Still, the energy requirement varies by much less than 11 folds.

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pondlife on January 28, 2008 - 3:20am Permalink | Subthread | Parent | Comments top

Ywish I can see at least 1 basic error in your calculations:

"Vicki", in your reference, is supplying the calories consumed by the person doing the activity.

Assuming the numbers are right [big assumption - but they sound OK], this IS NOT the energy applied to the load, but the metabolic calories.

I have heard figures of 25% max efficiency for striated muscle eg 25% work 75% heat loss. Add in unfavourable leverages and other losses [eg friction] and 10% useful work sounds about right

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Ywish on January 28, 2008 - 4:19am Permalink | Subthread | Parent | Comments top

pondlife --

According to my notes, the human muscle efficiency (ratio of the mechanical work performed to the metabolic cost) varies between 15% and [as much as] 30% [nearly three times the energy efficiency of average car engine.]

Here's a quote from http://www.fueleconomy.gov/feg/atv.shtml

Only about [12.6%] of the energy from the fuel you put in your tank gets used to move your car down the road

engine-efficiency

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Marty on January 28, 2008 - 8:10am Permalink | Subthread | Parent | Comments top

I did a very similar calculation in an article for the oildrum a few years back.

I agree that in order to compare apples to apples, you have to measure human output, not input. I used the wattmeter on Floyd Landis' bike (the Tour de France winner accused of androgen use), which registered 230 watts average for the whole riding time of the Tour. I divided by 2 for us less-in-shape people, and then assumed you could put out that power for 6 hours a day on weekdays (not counting breaks).

On the barrel-of-oil side, I used 20 gallons of gasoline from a 42 gallon barrel. Once again, you have to measure useful power output, not input calories, so I assumed it was being burnt in a 25% efficient engine in a car or piece of oil-powered equipment.

That works out to one barrel equals one year of human work. Of course, a human with a brain (which, incidentally, runs on 5-10 watts) could use that power output more strategically -- e.g., by pulling individual weeds instead of a plow -- but sometimes, you just need the power output straight up -- like when a load of concrete is hoisted up to the top of a building, or old concrete is crushed into gravel.

In the article, I also noted the difficult situation with non-renewable helium, given that I mostly do MRI for a living.

Marty

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Ywish on January 28, 2008 - 11:34am Permalink | Subthread | Parent | Comments top

Marty

That's good!

Incidentally, according to a number of different sources including:

1.Drubach, Daniel. The Brain Explained. New Jersey: Prentice-Hall, 2000.

and

2.Physics of Body. Macmillan Encyclopedia of Physics. New York: Macmillan, 1996.

The average human brain runs on 20-25W.

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thomas deplume on January 28, 2008 - 1:23pm Permalink | Subthread | Parent | Comments top

Looks like a violation of thermodynamic laws if you truly believe humans convert energy to work at 15-30% efficiency. The temperature difference between core body temperature and the skin is only 17 kelvins. With perfect mechanical efficiency that works out to only 5.48%. As the load increases the difference between core and skin temperature may decrease causing efficiency to drop further. From this low figure the energy needed for basal metabolism needs to be included. That 12% at the wheels starts to look pretty good.

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NoLogos on January 28, 2008 - 1:54pm Permalink | Subthread | Parent | Comments top

Humans are not pure heat engines. We take chemical energy that is captured by other organisms and convert it. Perhaps a wound-up spring is a useful analogy.

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