In maths, we have been exploring circles. We began by revising the vocabulary associated with circles – radius, diameter and circumference. We then practised our measuring skills by measuring circles and circular objects. We used tape measures to measure the circumference of circular objects. When measuring the circumference of circles on paper, we used string and a ruler.
On looking carefully at our measurements, we noticed that the diameter is always double the radius and also that the circumference was roughly three times the diameter.
After this, we practised our compass skills. We constructed circles of of different sizes and labelled the radius or diameter. Some of us went on to challenge our compass skills further by drawing concentric circles and circle patterns.
Having observed that circumference is roughly three times the diameter, we investigated this further by using string cut carefully to the length of the diameter. We lay this round the circumference and marked the circle. We were amazed that every single time we needed ‘3 and a bit’ diameters to go all the way around the circumference. We learnt that this number is called pi which has an approximate value of 3.14.
To explore this further, we read a book called ‘Sir Cumference and the Dragon of Pi’. This a fun story where pi is discovered as being a magic number that is the same for all circles.
After this, we thought about the challenges of finding the area of circles. We cut a circle into equal sized sectors and rearranged these to form a shape close to a rectangle. We were then able to find the approximate area of the original circle by measuring the length and width and multiplying. Some of us were then able to apply our algebraic reasoning to prove the formula: area of a circle = pi x radius squared.
