As my high school physics teacher once explained to me, energy comes in all sorts of different forms: heat, light, motion, electricity, and even the “potential” energy in chemical bonds and bowling balls perched on top of a downward sloping ramp. And yet, somehow, all of those different forms of energy were really all the same thing. Energy is energy, no matter what form it takes.

To prove the point, she explained, it’s quite easy to turn one form of energy into another. Car engines convert fuel into forward motion and heat; plants convert light into food; solar panels convert light into electricity; and the human body turns, say, Snickers bars into heat, motion, and work.

With me so far? Good. So let’s do a thought experiment.

Picture, for a second, a big ol’ SUV—say, a Lincoln Navigator—speeding along at over 70 miles per hour. It’s got a lot of “kinetic” energy (the energy of motion). Now, picture that SUV slamming head on into a brick wall. (Don’t worry, it’s being driven by crash test dummies.)

That’s a big, nasty crash, right?

Now, imagine that you could somehow capture all of the kinetic energy released in that collision, and convert it into a more familiar form: Snickers bars. (Yeah, it’s a little weird, but energy is energy. Or, if you prefer, you could measure the kinetic energy of the crash, convert that measurement into nutritional calories—the measure of food energy—and see how many Snickers bars you get.)

So in terms of energy equivalence, how many Snickers bars are there in a car crash? The answer is surprising…

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I’ve asked dozens of people this question over the last few months, and nobody’s guess has been remotely close. Typically, people guess in the thousands, or even millions, of Snickers bars.

But the answer is much smaller: one. A devastating car crash only represents as much energy as a single Snickers bar: 280 nutritional calories.

It hardly seems possible that one candy bar can pack so much punch. But remember, it takes only about a cup of gasoline to accelerate an SUV from standstill to highway speed. And most of the energy in that cup of gas is simply wasted—dissipated as engine heat or friction, rather than harnessed into forward motion. Given that, it’s not too hard to believe that there’s just a single Snickers bar worth of kinetic energy in a speeding SUV. Still, our gut tells us that that’s absurd, and that a car crash has to have much, much more energy than a Snickers bar.

The lesson here? When it comes to energy, our common sense is just plain dumb. We do OK with other parts of everyday reality: if someone asked us to guess how much time it’ll take to get to the store, or how much a car weighs, or how tall a house is, we’ll probably be pretty close. But ask us about energy, and we can be wrong by many orders of magnitude.

And that’s a real problem, since it makes it very difficult for us to set priorities around, say, energy efficiency. You might get way more bang-for-the buck sealing up leaks in windows and doors than from installing solar panels; but you can’t know that just by listening to your common sense. Sometimes, you need someone knowledgeable to help you figure out the best, most cost efficient energy investments.

Seems like a good green jobs opportunity to me…

Oh, and just FYI—Here are some other Snickers bar energy conversions (in round numbers):

* A hot bath: 10-20 Snickers bars

* A leisurely 10-mile bike ride: 1 Snickers bars

* A leisurely 10-mile drive: 56 Snickers bars.

* A stick of dynamite: 2 Snickers bars.

You can play around with this yourself: try this calorie counter for everyday activities, and this converter to turn various forms of energy into nutritional calories. And the one lesson I’ve learned from playing around with this: It doesn’t take much energy to produce light or motion, but heat is an energy hog! That’s why incandescent bulbs are so inefficient—most of the energy from electricity is turned into heat, rather than light.

Snickers photo courtesy of Flickr user Eddie~S under a Creative Commons license.