Why does Pi show up in so many diverse equations if it’s only related to a circle?

Question

Is Pi more than just a ratio for circles? Is there a easy way to understand the universality of Pi?

In: 1018

Answer 1

A number of good answers, but also consider how much we do that involves waves, or anything with a periodic system. We use the math of a circle to work in them, so light, a spring oscillation, sound, etc.