[Chemistry4me]

See if this has anything: http://ideas.4brad.com/holy-cow-walking-consumes-more-gasoline-driving

[John Chapman (OP)]

Wow, that really is amazing. So we use more gasoline eating extra food to get the calories to walk somewhere than we would driving there in a car. I have heard this before but it's the first time I've seen the figures. If you add up all the gasoline used by agriculture and industry to produce food then the food has a higher fuel footprint than your car:

If you eat a lot of beef or other livestock, and want to consider your incremental food as having come from beef, it’s around 10 miles per gallon. A Hummer does better!

There's so much significant stuff in that article that I'm going to have to print it off and read it a few times and consider it further.

It seems that it doesn't matter what you do you've got to contend with guilt. I suppose I'd better just get my spade out and grow my own food!
 

[mattyelle1]

Most efficient scooter: Yamaha Vino Classic, 1.5 L/100km    ( newbielink:http://www.totalmotorcycle.com/MotorcycleFuelEconomyGuide/best-scooter-MPG.htm [nonactive])

Human on Bicycle, 0.32 L/100km ( newbielink:http://en.wikipedia.org/wiki/Energy_efficiency_in_transportation [nonactive])

Mechanism for motion is the same (gears/transmission to wheels). Purpose is the same (move one human on flat surface).

Efficiency ratio: 1.5/0.32 = 4.7

Therefore, the human body is 4.7 times more efficient than a gasoline engine. Obviously many assumptions were made, but should be a fair ballpark figure.

[cheryl j]

It might depend on whether you consider heat wasted energy. It does serve a purpose in the body, but less so in an engine.

Here's an interesting fact I just read in a book about the brain by David Eagleman: When chess champion Gary Kasparov played against the computer called Deep Blue, Kasparov's brain's energy usage was about 20 watts compared to the computer's thousands of watts. Kasparov played the game at normal body temperature while Deep Blue was burning hot to the touch and required a large collection of fans to dissipate heat.

Of course that was a long time ago, but the brain is nevertheless remarkably energy efficient.