Shift Key Summer School: What Is a Watt?

What is the difference between energy and power? How does the power grid work? And what’s the difference between a megawatt and a megawatt-hour?

On this week’s episode, we answer those questions and many, many more. This is the start of a new series: Shift Key Summer School. It’s a series of introductory “lecture conversations” meant to cover the basics of energy and the power grid for listeners of every experience level and background. In less than an hour, we try to get you up to speed on how to think about energy, power, horsepower, volts, amps, and what uses (approximately) 1 watt-hour, 1 kilowatt-hour, 1 megawatt-hour, and 1 gigawatt-hour.

Shift Key is hosted by Jesse Jenkins, a professor of energy systems engineering at Princeton University, and Robinson Meyer, Heatmap’s executive editor.

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Here is an excerpt from our conversation:

Jesse Jenkins: Let’s start with the joule. The joule is the SI unit for both work and energy. And the basic definition of energy is the ability to do work — not work in a job, but like work in the physics sense, meaning we are moving or displacing an object around. So a joule is defined as 1 newton-meter, among other things. It has an electrical equivalent, too. A newton is a unit of force, and force is accelerating a mass, from basic physics, over some distance in this case. So 1 meter of distance.

So we can break that down further, right? And we can describe the newton as 1 kilogram accelerated at 1 meter per second, squared. And then the work part is over a distance of one meter. So that kind of gives us a sense of something you feel. A kilogram, right, that’s 2.2 pounds. I don’t know, it’s like … I’m trying to think of something in my life that weighs a kilogram. Rob, can you think of something? A couple pounds of food, I guess. A liter of water weighs a kilogram by definition, as well. So if you’ve got like a liter bottle of soda, there’s your kilogram.

Then I want to move it over a meter. So I have a distance I’m displacing it. And then the question is, how fast do I want to do that? How quickly do I want to accelerate that movement? And that’s the acceleration part. And so from there, you kind of get a physical sense of this. If something requires more energy, if I’m moving more mass around, or if I’m moving that mass over a longer distance — 1 meter versus 100 meters versus a kilometer, right? — or if I want to accelerate that mass faster over that distance, so zero to 60 in three seconds versus zero to 60 in 10 seconds in your car, that’s going to take more energy.

Robinson Meyer: I am looking up what weighs … Oh, here we go: A 13-inch MacBook Air weighs about, a little more than a kilogram.

Jenkins: So your laptop. If you want to throw your laptop over a meter, accelerating at a pace of 1 meter per second, squared …

Meyer: That’s about a joule.

Jenkins: … that’s about a joule.

Mentioned:

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Music for Shift Key is by Adam Kromelow.