# What Makes π Special

Build a measuring wheel whose every turn is exactly one metre, and meet π along the way

By nimble\-finch\-be2f978e

Topic: Maths

[Open the interactive Jig](https://ask.jig.com/j/M1IQzy8iXNcM)

## Transcript

### 1. What Makes π Special

Every circle hides the same number, π \(say “pie”\)\. Go once around any circle and you travel just over three times its width: about 3\.14 times\. Its digits go on forever and never repeat\. Let’s build a measuring wheel that puts π to work\.

Drag the scene to look around\.

### 2. 1 · Measure Across the Wheel

Hold the red stick across the wheel’s face, through its centre\. It fits exactly: the distance straight across a circle is called its diameter\. This wheel is 31\.8 cm across, a size chosen with π in mind\.

### 3. 2 · Lower the Fork

Stand the teal fork upright and lower it over the wheel, one arm on each side\. Line up the holes in the arms with the hole in the wheel’s centre\.

### 4. 3 · Fit the Axle Bolt

Push the yellow bolt through the front arm, the wheel and into the back arm\. Turn it clockwise three times until it is snug\. The wheel should still spin freely\.

### 5. 4 · Push In the Handle

Slide the handle into the socket on top of the fork until it clicks\. It leans back so you can push the wheel as you walk\.

### 6. 5 · Clip On the Counter

Press the counter onto the front arm\. It clicks once for every full turn of the wheel, so you never lose count\.

### 7. 6 · Roll One Turn: Meet π

Roll the wheel from the zero line for exactly one turn: it travels 1 metre\. Now lay the three sticks end to end beside it\. Three diameters fall just short, by 0\.14 of a stick\. That is π: every circle’s rim is 3\.14 diameters long\.

Press the button to roll it again\.

### 8. 7 · Measure Like a Pro

One turn is π times the wheel’s width, which makes exactly 1 metre\. Keep rolling and count the clicks: two clicks, two metres\. Surveyors, fence builders and sports\-field markers measure with wheels like this\.

### 9. π Is Everywhere

Anything round needs π: pizzas, cans, pipes and bike wheels\. Swings, waves and pendulum clocks repeat in rhythms that π describes\. NASA steers spacecraft using π to just 15 decimal places\.

Pi Day is 14 March, written 3/14 in the US\.