One of the challenges in explaining things is figuring out how to put something very unfamiliar in more familiar terms. You may not know what a Joule per second is, but you know what a Watt is — and a Watt is just another name for a Joule per second. It’s sort of like tight/loose and understeer/oversteer.
There are many different types of energy: chemical, electrical, light, sound, potential… etc.
Kinetic Energy is energy of motion. It takes into account how massive something is and how fast it moves.
- The faster a car goes, the more kinetic energy it has.
- The more massive a car is, the more kinetic energy it has.
The formula is:
You’ll notice speed is more important than mass because it factors into the equation twice.
We normally measure kinetic energy in Joules. A Joule is the amount of work it takes to move a 1-kg mass a distance of 1 meter in 1 second. If we plug the numbers for a NASCAR Sprint Cup race car into the equation, we get the following graph of Energy (in Joules) vs. speed (in mph).
Yeah… not exactly intuitive, right?
You can tell from the graph that a NASCAR race car going 170 mph has 4.45MegaJoules (meaning 4.45 million Joules) of energy. It’s a big number, so maybe it’s impressive… but what exactly does it mean?
Putting it in Context
I thought it might be helpful to compare the kinetic energy of a race car by comparing it to other things: a javelin being thrown, a flashlight, a gram of TNT, a food calorie, so I looked up some numbers and plotted them.
The first thing you’ll notice is that the energy scales are not even close. We’re talking MegaJoules with the racecar and this in only kiloJoules (a thousand times less.)
But something else should stand out to you. Mostly because I put that piece of data in orange.
Is that right?
Yes, it is. Right next to the energy contained in one gram of TNT is the energy contained in one food calorie. And both of those are about half the energy contained in a AA alkaline battery.
We call this ‘counterintuitive’, which is scientific terminology for WTF??? So, of course, I had to make some more plots.
I can’t help it. It’s how I think about things. Let’s see if we can find some other numbers, and some that are getting more in the range of a NASCAR race car.
The energy scale has increased a little bit. The first graph went up to 9000 Joules. This one goes up to 45,000 Joules.
Take a look at how much energy is contained in one gram of carbohydrate, protein or fat. (Note that a gram of butter is about a fifth of a teaspoon!) I put the food-related energies in orange, again, so they’ll stand out.
That’s a lot of energy.
But What About the Race Car?
We’re still nowhere near a fast-moving NASAR race car. So I wondered what might be something comparable in energy to the kinetic energy of a NASCAR race car.
Look what I decided on…
Candy. Yep. That’s a 250-calorie Snickers Bar there on the right. A good quality dark-chocolate Easter bunny (and yes, two were consumed as research for this blog) is about twice that many calories.
So using the unit of the dark-chocolate Easter bunny, let’s re-plot the kinetic energy of a NASCAR race car versus speed. This is the same graph as the first one, but instead of MegaJoules, I’m using a NIST-standardized dark chocolate Easter Bunny.
NIST, the National Institute of Standards and Technology, doesn’t have a standardized bunny. They have standards for a slew of other things, so you would THINK they’d have a standard for something as important as a chocolate Easter bunny. If they need help developing said standard, I would be happy to volunteer.)
So what does that mean? Well, first, it means that the human body needs one heck of a lot of energy. (And yet we still manage to eat too much!)
Second, it means that we can make a whole bunch of interesting equivalencies between the kinetic energy of a NASCAR race car going 190 mph and…
The last one ought to really get your attention. The same energy that is in almost three pounds of TNT is in 124 Jelly Beans. Wow…
Is There Something Serious Here…?
Yes, actually there is. Aside from a new appreciation of your body, remember the law of conservation of energy.
Energy can never be created or destroyed, only changed in form
So if you’re going 190 mph and you come to a stop, all that kinetic energy has to go somewhere. That’s what the SAFER barriers, the crunch zones, the skidding and the squealing are all doing — scrubbing off energy.
And in your body, it means that all the energy that comes in as food either goes out as your metabolism, your activities… or it sticks to your midsection.