An anemometer is an instrument used to determine the wind's force or speed. The Wright brothers used an anemometer to determine the wind's speed as they experimented with their flying machines.

You will build one type of anemometer called a cup anemometer. You will test the anemometer, record and make a graph of estimated wind speed. You also will learn about different types of anemometers.

STEPS TO FOLLOW:

Read the history information for this activity. Print out a copy of the data collection sheet and Beaufort Wind Strength Scale chart. Make the "Paper Cup Anemometer" following Steps 2-8 (Note: this is a separate lesson plan.) This cup anemometer is an example of a vertical-axis wind collector.

Take your anemometer outside. Watch it spin as the wind strikes it. Your anemometer is useful because it rotates with the wind. It need not be pointed into the wind to spin.

To calculate the velocity at which your anemometer spins, determine the number of revolutions per minute (RPM). Make a small mark on one of the cups. Using your data collection sheet, record the number of times that cup makes a complete revolution (a complete cirle around the pencil) in a minute. This number will be the revolutions per minute or RPM.

Calculate the circumference (in feet) of the circle made by the rotating paper cups. The circumference is equal to the diameter of the anemometer multiplied by the number p which is approximately equal to 3.1416. Measure the diameter of the anemometer from one cup to the opposing cup. Convert this number to feet. To obtain the circumference multiply this number by p. Alternately, you may use a tape measure to measure the circumference of the anemometer directly. (Either way you should obtain the same results.)

Multiply your RPM value by the circumference of the circle, and you will have an approximation of the velocity at which your anemometer spins (in feet per minute). Record this information on your data collection sheet. (Note: Other forces, including drag and friction, influence the calculation but are being ignored for this elementary illustration. The velocity at which your anemometer spins is not the same as wind speed.)

Examine the Beaufort Wind Strength Scale chart. What are your current wind conditions? Record this information on your data collection sheet.

Repeat this at different times in a day, on different days or in different wind conditions and record this information on your data collection sheet. Is there any pattern that you observe?

Graph the data on your data collection sheet. Plot anemometer RPM on one axis and the Beaufort scale on the other. Is there any pattern that you observe? You can use your graph to correlate the anemometer's RPMs to the wind's speed.

You may wonder, "If I have the Beaufort scale, why do I need the anemometer?" This is a very good question. Do you remember why the Wrights selected the Kitty Hawk area to experiment? It is because there was miles of sand with no trees, bushes or other obstructions to hit. Many of the entries on the Beaufort scale are based on observations of trees and other structures. Miles of sand but no trees at Kitty Hawk.