Wind: Measuring wind speed with a homemade anemometer
Hurricanes Charley and Frances have wreaked havoc on parts of the U.S. Understand some of the forces behind a hurricane's power with this experiment that measures wind speed.
Purpose/Hypothesis
In this project, you will make a simple anemometer and compare the wind speed measured by your anemometer with the wind speed measured in your region by the National Weather Service. The National Weather Service gathers wind speed and other weather information every 1 to 6 hours from about 1,000 land stations throughout the United States and its possessions. Meteorologists at the Weather Service use this information to make weather predictions, which are then broadcast over radio and television. The Service's weather stations use cup anemometers to measure wind speed.
Some television stations provide a live broadcast of the current wind speed; you might even see the speed change during the forecast. If you can tune in to one of these broadcasts, you can make your wind speed measurements simultaneously, thus eliminating the time variable.
Level of Difficulty:
Easy/moderate.
Materials Needed:
- metal or plastic protractor
- Ping-Pong ball
- 8 inches (20 centimeters) of strong thread
- transparent tape
- Approximate Budget: Less than $5. (Most or all of these materials should be available in the average household.)
Timetable:
15 to 20 minutes.
Step-by-Step Instructions:
- Tape one end of the thread firmly to the Ping-Pong ball.
- Tie the other end of the thread to the middle of the flat side of the protractor, as illustrated. The ball should hang down so the thread crosses the rounded side of the protractor. The numbers (angles) marked on the rounded side will indicate wind speed.
- Determine when the weather will be broadcast over a local radio or television station and whether it includes a live broadcast of wind speed.
- At the same time as a live weather broadcast or about 2 hours before a taped broadcast, take your anemometer outside. Stand in an open area, away from trees, buildings, and traffic.
- Hold the anemometer by one corner, with the flat side parallel to the ground.
- As the wind blows, note the angle of the farthest movement of the thread. Record it on a chart similar to the one illustrated.
- Use the scale provided to convert the angle to miles per hour (mph)
and record it on your chart:
Angle=mph
90° angle=0 mph
80° angle=15 mph
70° angle=20 mph
60° angle=25 mph
50° angle=30 mph
40° angle=35 mph
30° angle=40 mph
20° angle=50 mph - Take a second wind-speed measurement and record it on the chart.
- Add the wind speed from the radio or television broadcast to your chart.
- Repeat Steps 4 to 9 on two more days and record the results.
Summary of Results
Use the data on your chart to create a triple-bar graph comparing the three readings on each day. Then study your graph and chart and how accurately your anemometer measured wind speed. Were your own measurements on any day within 5 miles per hour (8 kilometers per hour) of those given in the radio or television broadcast? Write a paragraph summarizing your findings.
Troubleshooter's Guide
Here is a problem that may arise during this project, some possible causes, and ways to remedy the problem.
Problem: Your wind speed reading was much higher or lower than the one broadcast on radio or television.
Possible cause: You took your reading in a spot that is protected from the wind or a spot that serves as a natural wind tunnel, increasing its speed and force. Try again in a different spot.
Possible cause: You took your reading at a different time from the reading that was broadcast. Try calling the radio or television station and see if the forecaster or someone else will give you the current wind speed. Then quickly do your own reading.