Pies and circles

Dear Samarth,

I have always told you that there are two Pies in a circle. 

Actually, there is a greek alphabet pi, which is what we talk about when we say pie when we are talking about a circle.  Here's how it looks:

The circle is very interesting geometrical shape. There is a single thing that describes a circle: its "radius". If you gave someone the radius of a circle you have, that person can draw exact same size circle using that radius. 

You know what an angle is right? We measure the angle in units of degrees or radians. A circle has 360 degrees, but there is an interesting way of measuring the angle in radians. A "radian" is a measured differently:

If you walked around the circle on its edge, a distance that is the same size as the "radius" of the circle, the angle spanned by you is exactly equal to 1 radian. So how many "radians" are there in a circle. Exactly "2 pi" radians. 

Hence, we say that there are 2 pies in a circle. Now you know the real secret.

Love, 

Papa