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Science corner

Sophie Duncan brings pupils up to speed on wind strength

October is a windy month, but how windy is it? This activity will enable your students to make a cup anemometer and find out.

The cup anemometer was invented in 1846 by John Thomas Romney Robinson. The design is quite simple. Three or four metal hemispheres are mounted horizontally and fixed to a vertical spindle. As the wind blows, the cups spin around.

There are several ways you can make an anemometer and this project provides plenty of opportunity to test different designs and materials.

Take four paper cups, and remove their rims to make them lighter. Make a hole in each of the cups 3cm from the rim. These will be referred to as cups 1 to 4.

Take a fifth cup and remove the top third. Make four holes equal distances apart, 2cm from the cut edge. Take a plastic drinking straw and thread it through two opposite holes. Repeat with a second straw, using the other two holes. The two straws should form a cross on the inside of cup 5.

Cups 1-4 need to be attached to the ends of each of these straws. Push the straw through the hole in cup 1. Make a small fold in the end of the straw inside the cup and push it through to the opposite side. Sellotape or staple the folded end of the straw into position.

Repeat with cups 2-4. It is important to mount the cups so they are horizontal and all facing the same way. Mark one cup with a marker pen to distinguish it from the others.

Make a small hole in the base of the central cup. Slide a straight thin stick such as a flower cane through the hole and attach it to the two straws using a piece of Blu-tack. Take a straw and slide it on to the opposite end of the stick like a sheath. This allows the anemometer to spin around freely while your student holds the straw.

To calculate wind speed you can either calibrate your device - comparing the number of rotations to wind speed and drawing a graph - or you can do a rough calculation by measuring the number of rotations in a minute, and calculating the circumference of the device to find out the distance travelled.

Sophie Duncan is project manager for science at the BBC

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