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Kids Math
Circle Geometry
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Skills needed:
- Multiplication
- Basic Geometry
A circle is an important shape in geometry. There are circles all around us in the real world. We can learn a lot about the real world and how it works by understanding circles.
First, what is the official definition of a circle?
A circle is a shape that is made up of all the points on a plane (a flat surface) that are the same distance from a given point.
What does that mean?
Okay, so let's start out with the "given point". Let's pick a point on a flat surface, like this screen, for instance. We'll call it point A.
Now pick all the other points on the screen that are the exact same distance R away from point A.
Watch as we add in equal points in the movie below:
Wow, we get a circle!
Terms used in circle geometry:
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Radius - The radius is the distance from the center point and the edge of the circle. This is the same distance R we used to make the circle in our definition.
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Diameter - The diameter is a straight line that goes across the circle and through the center. It's twice the length of the radius. This gives u our first math equation for the circle:
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D = 2 x R
Also,
R = D/2
So the diameter is two times the radius and the radius is one half of the diameter.
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Diameter - The diameter is a straight line that goes across the circle and through the center. It's twice the length of the radius. This gives u our first math equation for the circle:
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Circumference - The circumference is the distance around the circle. We use the following formula to figure the circumference:
c = d * π
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Uh oh! What is this symbol π???
This symbol is called pi. It stands for a number that we use with circles. We won't go into the details right now, but let's just agree to use it and that it works for now. Okay?
π = 3.14…..
The decimals actually go on for a long time (forever), but we will round it off to 3.14. It's close enough.
Back to circumference; There are a few handy formulas we will use:
c = d * π
c = 2 * π * r
Where c = circumference, d = diameter, and r = radius.
Other Circle Geometry terms:
Sector - A sector is a section of the circle made by two different radii. Sort of like a piece of pizza or pie.
Chord - A chord is a line segment that joins two points on the circle. The diameter is a special type of chord that goes through the center of the circle.
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Advanced Kids Math Subjects
Statistics
Mean, Median, Mode, and Range
Picture Graphs
Algebra
Order of Operations
Exponents
Ratios
Ratios, Fractions, and Percentages
Geometry
Polygons
Quadrilaterals
Triangles
Pythagorean Theorem
Circle
Perimeter
Surface Area
Misc
Prime Numbers
Roman Numerals
Back to Kids Math
Back to Kids Study
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Kid's Poll |
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Which of these cities would you most like to visit on vacation?
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Joke of the Day |
Q: Knock, knock----Who's There?----Ashe----Ashe who?
A: Bless you!
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Today In History |
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Who was born on this day:
1952 Mr. T (Actor)
1981 Josh Hamilton (Baseball player)
What happened today in history:
1881 The American Red Cross is established by Clara Barton.
1927 Charles Lindbergh completes the first solo nonstop flight across the Atlantic Ocean.
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