Circle
A circle is easy to make:
Draw a curve that is "radius" away
from a central point.
And so:
All points are the same distance from the center.
circle draw
You Can Draw It Yourself
Put a pin in a board, put a loop of string around it, and insert a pencil into the loop. Keep the string stretched and draw the circle!
Drag a point!© 2018 MathsIsFun.com v0.87
Play With It
Try dragging the point to see how the radius and circumference change.
(See if you can keep a constant radius!)
Radius, Diameter and Circumference
radius diameter circumference: circle/diameter = pi = 3.14159...
The Radius is the distance from the center outwards.
The Diameter goes straight across the circle, through the center.
The Circumference is the distance once around the circle.
And here is the really cool thing:
When we divide the circumference by the diameter we get 3.141592654...
which is the number π (Pi)
So when the diameter is 1, the circumference is 3.141592654...
circle: diameter=1, circumference=pi
We can say:
Circumference = π × Diameter
Example: You walk around a circle which has a diameter of 100m, how far have you walked?
pi circle 100m
Distance walked = Circumference = π × 100m
= 314m (to the nearest m)
Also note that the Diameter is twice the Radius:
Diameter = 2 × Radius
And so this is also true:
Circumference = 2 × π × Radius
In Summary:
× 2 × π
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Radius Diameter Circumference
