What is a Circle?
Before we talk about chords and diameters, let’s first understand what a circle is.
A circle is a shape that is perfectly round, like a ball, a coin, or a wheel.
It has no corners and no edges.
All the points on a circle are at the same distance from the center.
Example: Think of a pizza.
If you place your finger exactly in the middle, that’s the center.
Every point on the edge of the pizza crust is the same distance from the center.
That’s what makes it a circle!
Important Parts of a Circle
To understand chords and diameters, we need to know some parts of a circle:
Center: The middle point of the circle.
Radius: The distance from the center to any point on the circle.
Example: The stick of a lollipop from the middle to the edge is like a radius.
Circumference: The boundary or edge of the circle.
Example: The round rim of your bicycle wheel.
These three parts will help us when we talk about chords and diameters.
What is a Chord?
A chord is a straight line that connects two points on the circle.
Imagine drawing a straight line across a circle from one side to another, but not always through the middle.
That line is called a chord.
A chord always touches the circle at two points.
Example: Take a round plate.
If you draw a line from one side of the plate to the other (but not necessarily through the middle), that’s a chord.
Features of a Chord
It must lie inside the circle.
Both ends of the chord are on the circle’s edge.
Some chords are short, and some are long.
What is a Diameter?
Now comes the special chord — the diameter.
A diameter is the longest chord of a circle.
It passes through the center of the circle.
It divides the circle into two equal halves.
Example: If you cut a pizza exactly through the middle, you are cutting along the diameter.
Difference Between a Chord and a Diameter
Let’s compare them so it’s clear:
Chord: Any line joining two points on the circle.
Diameter: A chord that passes through the center.
Chord can be short or long.
Diameter is always the longest chord.
Chord does not need to go through the center.
Diameter must pass through the center.
Example: A slice cut near the edge of a pizza.
Example: A cut straight across the middle of a pizza.
Relationship Between Radius and Diameter
There’s a very important connection:
Diameter = 2 × Radius
That means, if the radius of a circle is 5 cm, the diameter will be 10 cm.
Example:
If you have a round cookie with a radius of 4 cm, then its diameter will be 8 cm.
Fun Facts About Chords and Diameters
The longest chord in any circle is always the diameter.
All diameters of a circle are equal.
A chord closer to the center is longer than a chord farther from the center.
If you fold a circle along the diameter, both halves will match perfectly.
Real-Life Examples of Chords and Diameters
Let’s spot them in our everyday life:
Chords:
A line drawn across a round clock face (not through the center).
A rope stretched across a circular pond (but not exactly at the middle).
Diameters:
The line passing through the middle of a coin.
Cutting a circular cake into two equal halves.
The length across a bicycle wheel passing through its center.
Drawing Chords and Diameters – Activity for Kids
You can try this at home with just a paper, compass, and pencil:
Draw a circle using a compass.
Put a dot in the center (that’s the center of your circle).
Draw a line across the circle touching two points but not the center — that’s your chord.
Now, draw another line that passes through the center and touches both sides — that’s your diameter.
You’ll see the difference clearly between the two!
Examples with Numbers
Let’s solve a few simple examples:
Example 1:
A circle has a radius of 7 cm.
Find its diameter.
Diameter = 2 × Radius
Diameter = 2 × 7 = 14 cm
Example 2:
You cut a circular cake with a knife passing exactly through the middle.
What line did you make?
Answer: A diameter
Example 3:
You draw a line on a round coin but it does not pass through the center.
What is it?
Answer: A chord
Why Are Chords and Diameters Important?
They help us measure circles.
In real life, engineers use diameters to design wheels, pipes, bottles, and more.
Chords are useful in art, decoration, and construction when using round designs.
Quick Recap
A circle is a round shape with all points equally far from the center.
A chord joins any two points on a circle.
A diameter is a special chord that passes through the center.
Diameter = 2 × Radius.
Diameters are always the longest chords.
Fun Challenge for Kids
Take three round objects at home (like a coin, plate, and bottle cap).
Measure their radius and diameter using a scale.
Check if the diameter is always twice the radius.
Try drawing random chords on them and spot the longest one (the diameter).
Summary in Easy Words
Chords and diameters are parts of a circle.
A chord is any straight line across the circle.
A diameter is the biggest chord, going through the center.
You can see them in pizzas, wheels, coins, and clocks every day.
