Discovering π

Aim

To show that the circumference of any circle is about 3.14 times its diameter.

Apparatus

• Round objects (coin, bangle, plate, wheel)
• String
• Ruler

Method

1. Choose a round object.
2. Measure its diameter (d) with the ruler.
3. Wrap the string once round it and measure the string: this is the circumference (C).
4. Record the readings and work out C ÷ d.
5. Repeat for at least 4 objects and find the mean.

Conclusion

C ÷ d is almost the same for every circle: about 3.14. This number is called π, so C = πd = 2πr.