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

I have used 3.14 for calculating the volume of a cylindrical tank in cubic feet, and then Google converts it over to gallons.

Also, when something cylindrical was hard to measure its diameter, I wrapped a string around it, then measured the distance between the marks, divide by 3.14, and that was the diameter.