# What Makes π Special

How a rolling wheel, a pizza and a wave all reveal the same never\-ending number, π, no matter how big the circle is\.

By quiet\-panda\-565a40f7

Topic: Maths

[Open the interactive Jig](https://ask.jig.com/j/6XfijPHLa0Uk)

## Transcript

### 1. A number hiding in every circle

Measure around any circle, then measure straight across it\. Around is always a little more than three times across\. That little\-more\-than\-three is a famous number called pi, written π\.

Tap the wheel to give it a spin\. Drag anywhere else to turn the table\.

### 2. Roll out one turn

Press the button and the wheel rolls exactly one turn, painting the distance around its edge onto the track\. Then rods as long as the wheel is wide drop in beside the paint\. Three rods fit, with a small sliver left over\.

That sliver is the 0\.14 in 3\.14\.

### 3. Any size, same π

Use the slider to make the wheel bigger or smaller\. The distance around and the distance across both change\. But around divided by across never changes: it is always π\.

A tiny coin and a giant Ferris wheel share the same π\.

### 4. Digits that never end

The digits of π go on forever, and they never fall into a repeating pattern\. A mathematician named Johann Lambert proved this in 1761\. Computers have now worked out more than 300 trillion digits, just for the challenge\.

### 5. Pizza maths

π also tells you how much space a circle covers\. Make a pizza twice as wide and you get four times as much pizza, not two\. Switch sizes and count the small pizzas\.

Pizza makers, pipe builders and can designers all use π to size round things\.

### 6. Every turn makes a wave

Watch the glowing bead ride around the wheel while its height is traced out to the side\. One full turn draws one smooth wave\. Sound, light and the electricity in your home all travel as waves like this, so π appears whenever they are measured\.

### 7. How many digits does NASA use?

Spacecraft navigators at NASA use π to plan their paths\. Slide to use more digits on a circle as wide as Voyager 1's distance from Earth, and watch the miss shrink\. With 15 decimal places the error is only about 1\.5 centimetres\.

Just 37 decimal places would measure the whole visible universe to within the width of an atom\.

### 8. Happy Pi Day\!

Wheels, pizzas, waves and spacecraft all share one never\-ending number\. Next time you see a circle, look for the little\-more\-than\-three hiding inside it\. Pi Day is celebrated on March 14, written 3/14\.