What it shows
A survey of 30 classmates is shown as coloured bottle caps on a circle. If 12 chose cricket, cricket gets 12 out of 30 of the circle, which is 144 degrees, and the slices of the pie add up to the full 360 degrees of the class.
The science
A pie chart shows how a whole is shared out. Each category's slice is its share of the total turned into an angle: share times 360 degrees. With 30 students, each student is worth 12 degrees, so the angle for each game is 12 times the number who chose it. Pie charts are good for comparing parts to the whole, while a bar chart of the same data is better for reading exact numbers.
Materials
Cost: free. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- About 30 bottle caps in four colours, or caps painted
- A card circle of radius 15 cm
- A protractor and ruler
- Glue
- A survey sheet and a tally
- A bar chart on graph paper for comparison
Safety
This project uses safe, everyday materials. Still, read the rules below with a parent before you start.
Never use mains electricity: power models with cells, batteries or a low-voltage adapter. Sharp and hot tools, flames and lab chemicals need an adult or your teacher beside you. Keep magnets, button cells and small parts away from young children, and wash your hands after making.
Step by step
7 steps. Do them in order, and test each part before you go on to the next. Write what you notice in a notebook as you go.
Ask 30 classmates to pick one favourite game from cricket, kabaddi, football and badminton, and tally the answers.
Work out each game's angle: number of students times 12 degrees. For example 12 cricket gives 144, 8 kabaddi 96, 6 football 72 and 4 badminton 48. Check they total 360.
Draw the sectors on the card circle with the protractor, starting each new sector where the last one ended.
Glue one bottle cap of the right colour in each sector for every student who chose that game, arranged in rows from the centre.
Write the game, the count and the percentage on each sector: 12 out of 30 is 40 percent.
Draw the same data as a bar chart on graph paper and mount it beside the pie.
Add a key showing which colour is which game and the question asked.
What you should see
A pie chart whose cap counts match the tally and whose angles total 360 degrees, shown next to a bar chart of the same survey for comparison.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
01How many degrees does one student get in a class of 30?
12 degrees, because 360 divided by 30 is 12.
02If 15 of 30 chose cricket, what angle is the slice?
180 degrees, half the circle.
03When is a bar chart better than a pie chart?
When you want to read exact numbers or compare many categories; a pie shows shares of a whole.
04What should all the slices add up to?
360 degrees, or 100 percent.
Take it further
Survey a second class and make a pie of the same size, then compare the slices for each game.
Change one thing, measure what happens, and add a table or chart of your readings: that is what turns a model into your own investigation.
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