1. 1 Circle Perimeter Formula The circumference of a circle Click the mouse

2. 2 Click the mouse only when you see or If you click too soon you will miss the best bits. Click the mouse Click to see Click the mouse

3. 3 The circumference of a circle Click the mouse

4. 4 First we need  (pi) Is it….. 3. 14159265358979323846264338 327950288419716939937510582097 494459230781640628620899862803 482534211706798214808651328230 66470938446095505822172535…..? What is  ? Is it a number? Click the mouse

5. 5  Well… not exactly.  is a ratio. Click the mouse

6. 6 Pi is the number of times you must travel straight across the circle to go the same distance as all the way round the circle. Once across twice across So  is a bit more than 3. Click the mouse Click to see the paths three times across and a bit further!

7. 7 How can we be sure that  is a bit more than 3? For a regular hexagon, the distance all the way round is exactly 3 times the distance straight across the middle. 12 3 Click the mouse Click to see the paths

8. 8 And all the way round the circle is a little bit more than all the way round the hexagon. So all the way round the circle is a little bit more than 3 times straight across the middle. Circumference =  × Diameter Click the mouse Click to see the paths

9. 9 Click the mouse Summary Circumference =  × Diameter