Tuesday, February 15, 2011

Math and Intuition

When I read this quote:

one metric ton of CO2 ... is the amount a typical family car will emit every 10 weeks.

I did not believe it at first.  On order to generate a metric ton of C02, you would need to combine about a third of a metric ton of fuel with oxygen in the atmosphere.*  That is about 700 pounds.  I thought, 'There is no way that anyone burns that much gas in 10 weeks.'

But then I looked up how much a gallon of gas weighs.  It is about 7 pounds.  So 700 pounds is 100 gallons of gas, or 10 gallons a week.  Suddenly the figure seems much more plausible.

I guess it is easy to underestimate just how much weight we are pumping into our cars when we fill up the gas tank.  My car is about 70 pounds heavier after I fill up the tank.  Somehow that makes the fuel burning seem a lot more real.

*Any engineers or physicists reading this are probably horrified by this simple approximation.  I know that carbon and oxygen have different atomic weights, and I also know that real fuels have a lot of hydrogen, which turns into water.  But I don't feel like taking the time to look up the atomic weights and doing a proper calculation.  Think of my estimate as a lower bound on the amount of fuel you would need to burn.

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