Step by step
The question
Question: find the volume of a sphere (a ball) with diameter 12 m.
1 Find the radius
The diameter goes all the way across the circle.
The radius is half of it.
Half of 12 is 12 divided by 2.
12 divided by 2 is 6.
So r = 6 m.
2 Use the rule
Put the ball in a cylinder just as wide and just as high.
The ball fills exactly two thirds of that cylinder.
Worked out, that gives the rule for a ball.
The rule has r³: r times r times r.
Careful: it is not 3 times r.
π is a special number for circles.
It is about 3.14.
So the volume is V = 4/3 × π × r³.
Now put the numbers in: r = 6.
6³ means 6 times 6 times 6.
That is 216.
So V = 4/3 × π × 216.
Keep the numbers small: divide 216 by 3 first.
216 divided by 3 is 72.
So V = 4 × π × 72.
4 times 72 is 288.
So V = 288π.
We keep π in the answer.
That is the exact answer.
3 About how much
To see about how much, put 3.14 for π.
288 times 3.14 is 904.32.
So the volume is about 904.32 m³.
Let's look back.
First: find the radius.
Then: use the rule.
Last: about how much.