Wind speed meter (anemometer)
Paper cups on sticks, counting spins per minute, show whether your school site suits a wind turbine.
The big idea
Before building a wind turbine, you need to know how windy a place is. An anemometer measures it, and you can make one from cups.
You will need
Tick things off as you gather them.
Step by step
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Step 1: Cross the sticks
Tape two sticks together to make a cross, so they meet in the middle at right angles.
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Step 2: Fix the cups
Tape one cup to the end of each stick, all facing the same direction round the circle. The open sides must face the same way, so the wind catches them and pushes the cross round.
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Step 3: Mount on the pencil
Push a pin through the middle of the cross into the eraser of the pencil. Check it spins freely when you blow on it.
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Step 4: Choose a site
Fix the pencil upright in a stand and place it outside, in an open spot well away from walls and trees.
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Step 5: Count the spins
Watch the coloured cup and count how many times it goes round in one minute. Repeat three times and take the average.
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Step 6: Estimate the wind speed
Measure the distance r, in metres, from the middle to a cup. One spin carries a cup 2 × 3.14 × r metres. Multiply by your spins per minute and divide by 60 to get the cup speed in metres per second. The wind is usually two to three times faster than the cups.
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Step 7: Compare places
Repeat in different places: the playground, the roof, behind a building. Which is windiest? Which is best for a turbine?
What to look for
- Open, high places are windier than sheltered ones.
- The wind is gusty, so readings change from minute to minute.
- Taking an average gives a more reliable answer.
Why it works
Cups catch the wind more strongly on their open side than their rounded back, so the wind pushes the cross round. Faster wind spins it faster. Counting turns over a fixed time gives a measure of wind speed. Wind turbines make more power in stronger wind, and the power rises steeply: double the wind gives about eight times the power. A site needs steady wind, not just occasional gusts.
Try this next
- Take readings at different times of day and plot them.
- Compare with the wind speed in a weather report.
- Use your numbers to decide where your school could put a small turbine.
Link to the grid
Wind developers measure a site for a year or more before building. A windy site makes more electricity and pays for itself sooner.
Learn how the grid worksMore wind, water and muscle experiments
Paper or plastic bottle wind turbine
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Water wheel generator
Spoons or bottle caps on a wheel catch falling water and turn a motor to make electricity.
Pedal-powered generator
An old bicycle turns a DC motor to light bulbs and shows how much effort electricity takes.