About this video
Sal draws a circle and labels its center, radius, diameter and circumference. A radius goes from the center to any point on the circle, a diameter goes straight across through the center (two radii), and the circumference is the distance around the circle.
You'll be able to
- label the center, radius, diameter and circumference of a circle.
- explain that a diameter is made of two radii and passes through the center.
Key words
- center
- The point in the middle of a circle that every point on the circle is the same distance from.
- radius
- The distance from the center to any point on the circle; more than one are called radii.
- diameter
- A line straight across the circle through the center, equal to two radii.
- circumference
- The distance all the way around the circle, like the length of a string wrapped around it.
Transcript
Draw a circle and label the radius, diameter, center, and the circumference. Let me draw a circle. And it won't be that well drawn of a circle, but I think you get the idea. So that is my circle. I'm going to label the center over here. I'll do the center. I'll call it c.
So that is my center. And I'll draw an arrow there. That is the center of the circle. And actually, the circle itself is the set of all points that are a fixed distance away from that center. And that fixed distance away that they're all from that center, that is the radius.
So let me draw the radius. So this distance right over here is the radius. That is the radius. And that's going to be the same as this distance, which is the same as that distance. I can draw multiple radii. All of these are radii, the distance between the center and any point on the circle.
Now, a diameter just goes straight across the circle, going through the center. From one side of the circle to the other side, I'm going through the center. It's essentially two radii put together. So for example, this would be a diameter. You have one radii, than another radii, all one line, going from one side of the circle to the other, going through the center.
So that is a diameter. And I could have drawn it other ways. I could've drawn it like this. That would be another diameter. But they're going to have the exact same length. And finally, we have to think about the circumference. And the circumference is really just how far you have to go to go around the circle.
Or if you put a string on this circle, how long will that string have to be? So what I'm tracing out in blue right now, the length of what I'm tracing out, is the circumference. So right over here, that is the circumference. And we're done.
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