Measure Pi Yourself

Find a round object — a plate, a jar lid, a bicycle wheel. Wrap a string around its circumference and mark the length. Measure the diameter straight across. Divide one by the other. You will land near 3.14, and with careful measuring you can reach 3.142.

Try it on three different-sized circles. Every one gives the same ratio. That is the heart of the experiment: pi is not a human invention but a constant we discover in physical space.