A circle is a shape in which all its points are the same distance for the center.

Can you think of some objects that are shaped like circles?

( hint :        )

Before we start, let's take a look at some "circular" terms.

The point located in the center of the circle is called the origin. Notice that the circle has a letter in the inside next to the center.  This letter names the circle.  In my example given, the circle will be called "circle B".  

If I picked a point on the circle and drew a line from that point to the center of the circle, that would create a line of  radius (r).  Similarly, If I drew a line from the center of the circle to another point on the circle, that would also create a radius.

Notice that I now have two (2) radii ( pronounced ray-dee-eye), which is the plural form of the word radius.

I  have just created another part of a circle called the diameter (d).  The diameter is a straight line which originates at a point on the circle, passes through the center point or origin of the circle, and ends at a point on the opposite end of the circle.

The distance around a circle is called the circumference (C).  

There is a relationship that exists between the circumference and the diameter.  If you know the measurement of the circumference and divide it by the diameter, there is a constant number derived that we call Pi.

 This is the symbol for Pi... 

Pi is equivalent to 3.1459265898.... 

Let's use 3.14 or 22/7 to represent Pi.  (that's easier to remember and work with.)

What does the Energizer bunny and the number Pi have in common? (Hint: click here )