circumference = 2*pi*radius or pi*diameter
It is an arc
The circumference of a circle = pi*diametre = 2pi*radius
The equator.
Then they are similar.
Pi times the diameter of a circle gives its circumference.
The ratio of the circumference of a circle to its diameter is Pi. (3.14159)
It is part of a curve. If that curve happens to be a circle, then it is a fraction of a circumference but it need not be.
Any circle's circumference can be calculated with the formula 2(pi)*radius
Circumference is a special name for a circles perimeter. I think the answer you are looking for is radious.
Yes.
Yes.