Tuesday, April 22, 2008

Burn calories not carbon

(Not the most physically accurate choice of title, since carbon-burning produces calories of heat. But it was chosen by a student who hasn't had physics yet.)

Doug responded to the student with the following calculation:
Good idea! Can I refine the calculation a bit? We are, after all, burning organic compounds and creating carbon dioxide when we walk. Here's a back of the envelope calculation:

Assuming the food we eat is an average of 15:1 carbon to nitrogen ratio, 2% nitrogen content, and is around 900 calories per pound. (3500 calories per pound for fat)

1 pound/900 calories = x/100 calories = 0.11 pounds of food burned to walk a mile

.11 pounds of food x .02 = 0.002 lbs N

0.002 x 15 = 0.033 lbs carbon per mile added to the atmosphere from walking

C= 12 O2 = 32 12/44 = 27% carbon in carbon dioxide

X = 0.33 (44)/12 = 0.12 lbs of carbon dioxide added to the atmosphere from walking

Assuming 20 miles per gallon for gasoline:

19.6 pounds carbon dioxide per gallon

19.6/20 = 0.98 lbs per mile carbon dioxide added to the atmosphere by driving

No guarantees on the assumptions, and someone should check my math, but it looks like those who choose to drive should pick up nine passengers on the way.


From: Heidi Brugger
Burn Calories not Carbon!

Walk or bike to school day April 24th!!

On average there are 84 cars in the parking lots (for students and faculty commuting to school) lets try to make it 34!!!

walking burns about 100 calories per mile and biking burns about 30.
One gallon of gas burns bout 19.6 pounds of carbon dioxide.

Help the Planet and help yourself!!!

~If you live to far away try and carpool with a housemate

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