Experiments – Anemometer

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.

2.

 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

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:

 
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