ELI5: Explain Like I'm 5

Cylindrical coordinate system

Imagine you have a big playground with a fence around it. To describe where different things are in the playground, you can use different directions. For example, if someone is standing in the middle of the playground, you can tell them to go five steps to the left, and they will end up at the fence on the left side of the playground.

Now, imagine you are holding a ball in the air in the playground. You can use the same directions to describe where the ball is. But, you can also use another way to describe it - how high up it is and how far away it is from the person in the middle of the playground.

To do this, we can use the cylindrical coordinate system. It has three parts - the distance from the person in the middle of the playground (which we will call the radius), the angle from a fixed direction (which we will call theta), and how high up it is (which we will call z).

So, to describe where the ball is using the cylindrical coordinate system, you could say it is five steps away from the person in the middle of the playground (radius), it is 30 degrees to the right from a fixed spot (theta), and it is two feet off the ground (z).

This is useful because it helps us describe things that are not just on a flat surface, like the ground of the playground. We can use it to describe things like antennas on towers, or to figure out how much paint we need to cover a weird-shaped object.