Measuring circles to see pi

Here's a fun video to inspire you!

The definition of π is circumference / diameter. Let's see that in action. There are a few ways to do that:

1. Get a flexible measuring tape. (Sewing stores have them.) Measure around a circular object, and also across the center. Use a calculator to divide those numbers. If your answer is between 2.9 and 3.4, you did a pretty good job of measuring!

2. Make a nice dark mark on the side of a spool, mark it up enough so it will leave a mark on paper. When you roll that spool along a line, you see the mark and then a ways away you'll see it again. The distance between those is the circumference. Now hold your spool on end, and see how far along that line you go using the diameter (across). How many times does it take to go along the whole circumference? (It should be 3 times plus a little bit.)

3. Put chalk on a wheel (across the tire, at one spot), and roll it along a line, so that you see two chalk marks on the line. Measure how far apart they are, and then measure the diameter of your wheel. Divide.  

4. Can you think of another way to measure around a circle and across?

(Most people think π is 3.14... But that's not the definition. It's just an approximate value.)