We call this distance along the widest point of the circle, the diameter.

Now, let's ask another question.

Actually, never!

Well, that's the same thing as g plus h.

If you were to put a tape measure to go around it and someone were to ask you what is the diameter of the circle?

OK, this is a neat property of circles.

We can multiply both sides of this by the diameter and we could say that the circumference is equal to pi times the diameter.

Well if this whole thing is your minor axis or maybe you could call your minor diameter if this whole thing is your minor diameter it's called minor, because it's the shortest of all of the diameters of this ellipse.

Now, we know how the diameter and the radius relates, but how does the circumference relate to, say, the diameter.

So we're worried about the ratio let me write it like this.

Select the segment whose length gives the diameter of the new circle...

Diameter

So maybe the circumference is always three times the diameter.

Construct a circle with the diameter given by the length of this segment

Is it possible to determine the diameter from the circumference?

A circle defined by its center and the length of a segment as the diameter

Where r is the radius of the sphere.

It has a very easy relationship with the radius.

Right there.

And then they measure the radius of the circle right here or the diameter of that circle, and they'd say oh, the diameter

That's a, that's a ninemile radius.

Circle by Point Radius

It is a two level style round burial mound, 23m diameter (lower level), 18m (higher).

And once again, the ratio of the circumference of the diameter was roughly 3.

So this is r squared, this is the radius squared.

What's our radius?

And so for area we need to know the radius 'cause area's pi R squared, so we can figure out the radius from the circumference by saying, well circumference is equal to two times pi times the radius of the circle, or if you say 36 pi, which we were told this is the circumference, is equal to two times pi times the radius.

Try to measure a circle.

Vertical spacing

Circle radius

Vertical Radius

Vertical Radius

dabs per actual radius

Cut a semicircle with a diameter of 12 centimeters.

Now, it's obvious that a circle's circumference would get smaller or larger along with its diameter, but the relationship goes further than that.

Now what is the radius?

Radiotelescope diameter

These are just stars.

We call that word the circumference of the circle.

Regardless of what kind of ID gripping jaws you are using

So we know, or I'm telling you, that the ratio of the circumference to the diameter when I say the ratio,

What is the diameter of the circle?

But this the current version of it, is a flying airship that is about 35 meters in diameter, about 110 feet in diameter.

Let's say that on this circle they measured around it and they found out that the circumference is 6 centimeters, roughly we have a bad tape measure right then.

In fact, the ratio between the two, the circumference divided by the diameter, will always be the same number, no matter how big or small the circle gets.