Circles
Pi = π
The number π is a mathematical constant, approximately equal to 3.14.
It is defined in geometry as the ratio of a circle's circumference to its diameter, and also has various equivalent definitions.
The
number appears in many formulas in all areas of mathematics and physics.
The radius of a circle = 1/2 diameter (r = 1/2 d)
The circumference of a circle = pi x diameter (c = π x d)
or circumference = 2 x pi x radius (c = 2 x π x r)
The area of a circle = pi x radius2 (a = π x r2)
For example:
Harry's bicycle wheel has a diameter of 50cm.
What is the circumference of Harry's bike wheel? (note: use π = 3.14)
c = π x d
c = 3.14 x 50
c = 157 cm
If Harry travels 100 metres on his bicycle, how many times does his wheel turn?
Convert metres in centimetres first: 100 x 100 = 10,000 cm
Distance ÷ circumference = number of turns
10000 ÷ 157 = 67.7
Harry's wheel turns 68 times for him to travel 100 metres.
