Of Car Crashes and Snickers Bars
Pop quiz, hotshot. Using the caloric energy content of a candy bar (e.g. Snickers, at 250 food calories), what is the kinetic energy of a two-ton behemoth SUV traveling at about 70 mph? A first-order approximation is fine — no need to worry about more than one significant digit.
Got it? Think of your number and then proceed to the analysis.
Let’s establish our standard. A food Calorie is a kilocalorie, and there are 4.184 Joules per calorie, making a Snickers bar the equivalent of about (1000 x 250 x 4) a million Joules of energy. More than you thought? “A food calorie is a kilocalorie” throws a lot of people off.
Now let’s calculate our kinetic energy. 70 mph is a little over 110 kph, which is about 31 m/s, and a ton is around 1000 kg. 1/2mv^2 gives us about … a million Joules.
One candy bar.
Some other comparisons for scale: Raising a 1 kg mass in earth’s gravity is about 10 Joules for every meter. Or a fairly large human, with a mass of 100 kg — that’s a kiloJoule per meter. One Snickers-bar would be able to raise that person a kilometer. Food has a lot of energy stored in it — the comparison in the article mentions that it only takes a cup of gasoline to get that SUV moving at 70 mph, which means that gasoline has a pretty high energy density as well. Which is one of the problems in trying to replace it with an alternative, like electricity.
So food has a lot of energy in it. What do we do with it all? Much of it goes into maintaining our body temperature. We radiate it away at about 100 Watts, which is about 8.5 million Joules every day.
Burn food not fuel. Hmmmm. Burn people not fuel? Wait! Wait! Burn dead plants not fuel. The hope for the future is coal! Now, eliminate all the Enviro-whinerism in the middle.
I usually get rid of my 100 Watts through a combination of evaporation and convection. Radiation’s not too efficient in most environments.
uncle al: burning coal is only a chemical reaction. you get more energy released via nuclear reactions. every care should be outfit with a Mr. Fusion device so we can time travel to the future where energy is plentiful and fairies dance around and give out sugar plumb rainbows. and we have national healthcare.
I think the answer is drink petrol!
The energy in food is tiny compared to the energy in matter. It always amazed me that the Hiroshima bomb did all that destruction by converting 0.6 gram (about an aspirin) into energy.