Parts of a circle: what children learn
In this game children match descriptions and measurements to the parts of a circle. Some cards give a radius and ask for the diameter, or the other way round, so children practice doubling and halving.
Enrichment: radius, diameter and circumference are introduced in Common Core 7.G.B.4. This game only names the parts and links radius and diameter.
How to play
Pick a card on the left, then the card on the right that matches it. Each game has 6 pairs. Wrong matches are counted as mistakes, and you get three stars for a game with no mistakes.
Step by step
- Radius. The distance from the center to the edge.
- Diameter. A straight line from edge to edge through the center. It is twice the radius.
- Circumference. The distance all the way round the edge.
- Double or halve. Diameter = 2 × radius. Radius = diameter ÷ 2.
Worked examples
Example 1: a straight line from edge to edge through the center
Working: It goes right across through the middle.
Answer: diameter
Example 2: radius 7 cm
Working: Double the radius: 2 × 7 = 14.
Answer: diameter 14 cm
Example 3: diameter 30 cm
Working: Halve the diameter: 30 ÷ 2 = 15.
Answer: radius 15 cm
Common mistakes and how to fix them
- Mixing up radius and diameter. Remember the diameter goes all the way across, so it is the longer of the two.
- Drawing a 'diameter' that misses the center. A diameter must pass through the center.
- Thinking the circumference is a straight line. The circumference is the curved edge of the circle.
Activities to try at home
- Measure the radius and diameter of plates and lids.
- Wrap string round a tin to measure its circumference.
- Draw circles with a compass or a pin and string.
Ideas for the classroom
- Students fold a paper circle to find its center and diameter.
- Measure several circular objects and compare their diameter and circumference.
- Draw circles with a compass from a given radius.
Free printable game and worksheet
The free printable starts with a game sheet, such as a color-by-answer picture, an answer maze or a secret-code joke, followed by a worksheet. Both use the same checked questions as the online game, and the answers are on the last page. Print it, or save it as a PDF from your browser’s print menu.
Open the free printable game and worksheet
Frequently asked questions
How should I choose this game for my learner?
Enrichment: radius, diameter and circumference are introduced in Common Core 7.G.B.4. This game only names the parts and links radius and diameter.
Can it be played with a keyboard?
Yes. Tab to a card, press Enter to pick it, then pick its partner.