Today is rung 4 of 5 on this topic
Circles — circumference, area and where pi comes from
Can do: Uses the circumference and area formulas correctly and knows which is which.
Why it matters
The formulas get swapped constantly. Measuring pi themselves is what makes the difference stick.
What it looks like when it's wobbly
Uses 2πr for area, and squares the diameter instead of the radius.
⏱️ Two-minute check
"A circle with radius 5 — circumference and area?"
Solid looks like: About 31.4 and about 78.5, with the right units.
The full activity for this topic · 25 minutes
Measure Pi Yourself
StringA rulerRound objects: tins, plates, lids
- 1Measure the circumference of five round objects with string, and the diameter with a ruler.
- 2Divide circumference by diameter for each. Every answer is about 3.14.
- 3That's the discovery — pi is a ratio, not a magic number.
- 4Use the mnemonic to separate the formulas: area has the square, and area is measured in squares.
- 5Calculate a real one — the area of a pizza, or how far a wheel travels in one turn.
If it's too hard
Circumference only, from measurement.
If it's too easy
Semicircles and composite shapes, and finding the radius from a given area.
Say this
"Area is measured in squares — so which formula has the square in it?"