Make your own Anemometer
For measuring wind speed
Equipment
◊ 30cm of strong THREAD or fishing line
◊ A PING PONG or other small, light, plastic ball
◊ SELLOTAPE
◊ PROTRACTOR
◊ A piece of strong CARDBOARD
15cm x 10cm
Method
1. Stick the protractor to the cardboard with sellotape, with the straight edge at the top of the card.
| string angle degree | 90 | 80 | 70 | 60 | 50 | 40 | 30 | 20 |
| wind speed m/s | 0 | 3.6 | 5.3 | 6.7 | 8.1 | 9.4 | 11.4 | 14.4 |
2. Write the above wind conversion chart onto the cardboard.
3. Using sellotape attach the thread to the ping pong ball. Tie or glue the other end of the thread to the centre of the top edge of the protractor.
4. Hold the cardboard in the direction that the wind is blowing, so the ball is caught by the wind. You will see the thread makes an angle that you can measure on the protractor.
Convert the angle the thread makes to a wind speed using the conversion chart.
If you have one, compare your readings to those made with a ‘real’ anemometer – how does it compare? Otherwise, compare your readings with the Beaufort Scale.
The Beaufort Scale
| Wind Force | Description | Speed (m/s) | Speed (knots) | Specifications |
| 0 | calm | 0-0.2 | 0 | Smoke rises vertically |
| 1 | light air | 0.3-1.5 | 1-3 | Direction shown by smoke drift but not by wind vanes |
| 2 | light breeze | 1.6-3.3 | 4-6 | Wind felt on face; leaves rustle; wind vane moved by wind |
| 3 | gentle breeze | 3.4-5.4 | 7-10 | Leaves and small twigs in constant motion; light flags extended |
| 4 | moderate breeze | 5.5-7.9 | 11-16 | Raises dust and loose paper; small branches moved. |
| 5 | fresh breeze | 8.0-10.7 | 17-21 | Small trees in leaf begin to sway; crested wavelets form on inland waters. |
| 6 | strong breeze | 10.8-13.8 | 22-27 | Large branches in motion; whistling heard in telegraph wires; umbrellas used with difficulty. |
| 7 | near gale | 13.9-17.1 | 28-33 | Whole trees in motion; inconvenience felt when walking against the wind. |
| 8 | gale | 17.2-20.7 | 34-40 | Twigs break off trees; generally impedes progress. |
| 9 | strong gale | 20.8-24.4 | 41-47 | Slight structural damage (chimney pots and slates removed). |
| 10 | storm | 24.5-28.4 | 48-55 | Seldom experienced inland; trees uprooted; considerable structural damage |
| 11 | violent storm | 28.5-32.6 | 56-63 | Very rarely experienced; accompanied by widespread damage. |
| 12 | hurricane | 32.7+ | 64+ | Devastation |
For more advanced students
Can you do your own calculation to relate wind speed to the angle of the string?
Think about the forces acting on the ping pong ball:
