The circumference of a circle Circle Formulae 1 The circumference of a circle Tandi Clausen-May Click the mouse

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The circumference of a circle Click the mouse Tandi Clausen-May

What is  ? First we need  (pi) Is it a number? Is it….. 3.14159265358979323846264338 327950288419716939937510582097 494459230781640628620899862803 482534211706798214808651328230 66470938446095505822172535…..? Click the mouse

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

So  is a bit more than 3. Once across twice across three times across 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. Click to see the paths Once across twice across three times across and a bit further! So  is a bit more than 3. Click the mouse

How can we be sure that  is a bit more than 3? 2 1 For a regular hexagon, the distance all the way round is exactly 3 times the distance straight across the middle. Click to see the paths Click the mouse

Circumference =  × Diameter 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. Click to see the paths Circumference =  × Diameter Click the mouse

Summary Circumference =  × Diameter Click the mouse

Now watch Circle Formulae 2 The area of a circle Tandi Clausen-May