Wind Speed from a Cup Anemometer: Robinson's One-Third Law (1850)

The cups of a cup anemometer move at one third of the wind's speed. Count the turns in a minute and the notebook turns them into miles per hour and metres per second. Result: the wind speed, from Robinson's portable instrument (cups on a 5.6 in radius: turns per minute / 10 = mph). Source: T. R. Robinson, Transactions of the Royal Irish Academy vol. 22 (1850), pp. 158, 168-169. Photo: NOAA, public domain.

Beginner

30 minutes

Instructions

Set up in the wind

Stand the cup anemometer in the open wind. Robinson's portable one: four hemispherical cups 3.1 in across, centres on a 5.6 in radius, turning a counter (an endless screw driving two wheels of n and n+1 teeth). Four cups worked better than five or three.

Tools needed:

Cup Anemometer

Atmospheric Air - Earth

Count one minute

Count the revolutions in one minute, from the counter or by watching one cup. Ours: a stopwatch.

Tools needed:

Cup Anemometer

Mechanical Stopwatch

Work out the wind speed

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Tools needed:

Cup Anemometer

Mechanical Stopwatch

Tools Required

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Cup Anemometer
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Atmospheric Air - Earth
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Mechanical Stopwatch
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