 Now we look at measurements of length, both the dimensions and the units. Any measurement of how far something is is the same basic type of dimension, and we call that dimension length. The generic notation for the dimension of length is a capital L, or in some textbooks L with square parentheses around it. When we talk about length or distance, they're both the measurement of how far. If we think of length as how far from one side to another. So, for example, for a piece of paper, it's 11 inches from the top to the page to the bottom of the page. That's the length of the paper. Or the bowling alley is 18 meters long, really means from the start of the bowling alley all the way down to the end of the bowling alley is 18 meters. For distances, it's how far one point to another. So, for example, it's 47.5 miles to Columbia. From here, so that's your distance. Positions are actually the same type of thing as well, because we can think of a position as how far from a fixed reference point. So that might be three meters to the right of the origin, or 2.5 feet above the floor. So those positions are really also measuring how far something is. Now there's a variety of quantities that all count as lengths, and we've seen a few of these already. But it's length, width, and height. So just because we call it length, doesn't mean that width and height aren't also measurements of those sorts of distances. Same thing, we can do radiuses and diameters and circumferences and encircles. Even a curved path where it's wiggling all over the place, how far is it along that path? All of these things are considered to be the same dimension of length. Now when we start measuring lengths, we have to have units with all of our values. The number by itself doesn't matter. And you're familiar with a lot of the variety of ways we can measure lengths. In meters, kilometers, miles, feet, inches, yards, some of those are metric units, some of them are English units. For the SI system, we're going to use a standard unit of meters as our base for measuring any kind of length. That wraps up our brief discussions of lengths.