How to Spin Pi
Happy Pi Day from me and my hula hoops!
I tried to put this post out on March 14th, 1:59pm 2026 cause the first few digits of π are 3.1415926, but you know, life happened! Can you believe that with computers we have been able to compute 105 trillion digits of π, but there’s still no pattern appearing from them? I tried to put my spin on this incredible constant, with my hula hoops!
With these animations, I want to share two simple insights. That when you spin a hula hoop, you literally spin π! π is simply put, the ratio of the circumference and the diameter of a circle. π = circumference / diameter. And, that no matter how big or small the hula hoop is, π remains constant!
Here are three hoop moves where you can spin π!
1. Isolations and folds
An isolation is a hoop move where it looks like the hoop is levitating, almost like magic! The physics of this is fascinating (more on this another day). You keep the hoop in front of you, face in the center, and drive it by pushing along the circumference.
This also brings up radians! Unlike degrees, radians are native to circles. a full rotation is exactly 2π radians. So in an isolation, the diameter spins 2π. π is in the rotation itself.
And adding the fold after the isolation is moving the hand across the diameter. So this isolation + fold combo is my more literal ode to π — first tracing the circumference, then the diameter!
2. Chest Rolls and cycloids
This is reminiscent of rolling a wheel on the floor. If you track one point on the circumference, when it reaches the floor again after one full rotation, the distance that point has travelled is 2πr! The shape traced by this point is called a cycloid. The center meanwhile travels in a straight line. I recreated this whole thing on my body with a chest roll!
3. Waist Hooping
When you spin a hoop around your waist, the most common hooping trick, you are spinning the circumference around your waist! Since the circumference is 2πr, you are quite literally spinning π! And no matter how big or small your hoop is, π is always the same.
I also want to leave you with three books that made me connect hoop tricks with maths, specifically the isolation and π connection.
The first is Francis Su’s Mathematics for Human Flourishing, recommended to me by my professor in Grad School, Vineeta Rath! From my learning journal: “While reading this book, I started thinking of metaphorical and literal connections between hoop tricks and math. For example, I realised that a hoop trick called an isolation is actually experiencing the circumference of a circle in motion! I thought of this when he spoke about math exploration as a continuous cycle passing from one phase to the other and back again.”
The second is Is Maths Real? by Eugenia Cheng! She has a fun rant about mathematicians being too irrational about π day.
And the third is Infinite Powers by Steven Strogatz. I reached a page about circles and π on March 11th, just a few days before π day, when I was wondering if I should push myself to make this post and animation!
I’ve always been scared to write about π, because it feels so infinite, beautiful, perfect. And it is a bit irrational (pun intended) to think that I can do justice to this constant. So I hope you folks have a radian day, this π day! 😄
- sPInfinity