Food contains a lot of energy. Sometimes it's instructive to think about just how much energy is represented by what we eat. Consider, if you will, the Oreo Rocket. It's powered by Oreo cookie filling and an oxidizer. There are other rockets powered by sugar, and of course nowadays we're hearing about the use of biofuels for all kinds of applications.
I think it's instructive to do the math: a 12-ounce can of Coke contains 155 calories. Of course, when we talk about food, that's really kilocalories. A kilocalorie is equal to about 4.2 kilojoules, so that Coke packs a walloping 650 kilojoules of energy. How much energy is that? It's enough to accelerate that can of Coke to a velocity of almost 2 kilometers per second, or roughly Mach 7.
So why can't I chug down a can of Coke and then throw the rest of the six-pack at hypersonic speeds? I've got the energy, right? Well, it's a sad fact that human bodies are pretty inefficient. At best we manage about 25 percent efficiency, and we can't store a lot of energy for very rapid release.
This has an interesting implication for biofuels: it's actually a more efficient use of energy to burn food than to eat it. That's good news if you're lazy and prefer to let machines do the hard work. But it's bad news if you're hungry . . .
A tip of the hat to the commentors on this post at Transterrestrial Musings.
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