- Circle
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.
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.
You Can Draw It YourselfPut 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!
Radius, Diameter and Circumference.
The Radius is the distance from the center to the edge.The Diameter starts at one side of the circle, goes through the center and ends on the other side.
The Circumference is the distance around the edge of the circle.
And here is the really cool thing:
When you divide the circumference by the diameter you get 3.141592654...
which is the number π (Pi)
So when the diameter is 1, the circumference is 3.141592654...
The Circumference is the distance around the edge of the circle.
And here is the really cool thing:
When you divide the circumference by the diameter you get 3.141592654...
which is the number π (Pi)
So when the diameter is 1, the circumference is 3.141592654...
We can say:
Circumference = π × Diameter
Example: You walk around a circle which has a diameter of 100m, how far have you walked?Distance walked = Circumference = π × 100m
= 314m (to the nearest m)
Circumference = π × Diameter
Example: You walk around a circle which has a diameter of 100m, how far have you walked?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
RememberingThe length of the words may help you remember:
Diameter = 2 × Radius
And so this is also true:
Circumference = 2 × π × Radius
RememberingThe length of the words may help you remember:
- Radius is the shortest word
- Diameter is longer (and is 2 × Radius)
- Circumference is the longest (and is π × Diameter)
NamesBecause people have studied circles for thousands of years special names have come about.
Nobody wants to say "that line that starts at one side of the circle, goes through the center and ends on the other side" when a word like "Diameter" would do.
So here are the most common special names:
Nobody wants to say "that line that starts at one side of the circle, goes through the center and ends on the other side" when a word like "Diameter" would do.
So here are the most common special names:
LinesA line that goes from one point to another on the circle's circumference is called a Chord.
If that line passes through the center it is called a Diameter.
A line that "just touches" the circle as it passes by is called a Tangent.
And a part of the circumference is called an Arc.
If that line passes through the center it is called a Diameter.
A line that "just touches" the circle as it passes by is called a Tangent.
And a part of the circumference is called an Arc.
Slices
There are two main "slices" of a circle
The "pizza" slice is called a Sector.
And the slice made by a chord is called a Segment.
There are two main "slices" of a circle
The "pizza" slice is called a Sector.
And the slice made by a chord is called a Segment.