[Dr. Scott W. Tinker] We looked at how electricity is made, now we're going to look at how we use it. You just flip the switch, right? The light's not on because there's no electricity. Every time we turn a light on or anything else, there's a generator turning somewhere to power it. And whenever we turn on more lights, we have to generate more electricity, and the more electricity we need, the more generators we have to turn on right at that very instant. We have to meet our demand for electricity literally by the minute. In fact, this is exactly what happens every single day. We call it the demand curve. At night when people are sleeping, there's still electricity demand. Street lights, refrigerators, cell phones being charged. We call that baseload. It's the minimum amount of electricity needed to power the things that are running all night, and mostly those are charged by coal-fired power plants and nuclear power plants. And then people wake up, factories and restaurants open, electricity demand grows towards the peak in the middle of the day when air-conditioning demand is highest. This is met by adding more and more generators. Lots of natural gas generation comes on and some major hydro plants. This can also be meant by wind and solar, depending on the wind and sun conditions of the day. Demand falls in the afternoon people go home eventually, they go to bed, some of the generators are shut down, and we're back to baseload power. The demand curve drives the entire electricity system. It determines what kind of generators we can run, when, and where. This simple concept is one of the most important things you can know about electricity.