How Does a Wind Meter Work?
AbstractOn a windy day it is hard to keep your hat on! The power of the wind can even be strong enough to power large wind turbines to make electricity! In this experiment, find out how you can make your own instrument to measure the speed and power of the wind. How does it work?
Sara Agee, Ph.D., Science Buddies
Watch CYBERCHASE on PBS KIDS GO! Check local listings or visit pbskidsgo.org/cyberchase. CYBERCHASE is produced by THIRTEEN in association with WNET. All rights reserved. CYBERCHASE is a trademark of THIRTEEN. The PBS KIDS GO! logo is a registered mark of PBS and is used with permission.
In this experiment you will investigate how the speed of the wind is measured by an anemometer.
Weather is happening all around us every day. But isn't it nice to know the weather ahead of time? Suppose you have a soccer game this weekend, what is the chance of rain? When you watch the weather forecast on the local news, you are watching the results of weather data that has been gathered by a meteorologist, who will use the data to try and predict the weather.
A meteorologist measures weather patterns in the atmosphere to predict the weather forecast ahead of time. To track changes in the weather, a meteorologist uses weather instruments at a weather station. There are many different weather instruments, each made to measure a different feature of the weather:
- a thermometer to measure temperature
- a barometer to measure air pressure
- a hygrometer to measure humidity
- a rain gauge to measure precipitation
- an anemometer to measure wind speed
- a wind vane to measure wind direction
An anemometer is used to measure wind speed. Speed is how fast or slowly something is moving. But what exactly is wind? Wind is movement in the air that can be seen or felt. Wind occurs when air moves from a high-pressure area (where there are more molecules) to a low-pressure area (where there are fewer molecules). See the CYBERCHASE episode, by PBS KIDS GO!, and watch as the CyberSquad heads to the Northern Frontier to solve a mystery by measuring and comparing wind speeds! Then get ready to test winds yourself. In this experiment, you will make your own wind meter, or anemometer. An anemometer is useful because it rotates with the wind. To calculate the speed, or velocity, at which your anemometer spins, you will determine the number of revolutions per minute (RPM), or how many times the anemometer spins a full circle from where it started in one minute. To test your anemometer, you will set a fan at different speeds and count the revolutions per minute of your home-made anemometer. How well will it work?
Terms and Concepts
To do this type of experiment you should know what the following terms mean. Have an adult help you search the internet, or take you to your local library to find out more!
- Revolutions per minute
- How does an anemometer work?
- Will high speed winds increase or decrease the number of turns of an anemometer?
- How can the number of turns and length of time be used to calculate wind speed?
- The University Corporation for Atmospheric Research (UCAR). (n.d.). Web Weather for Kids. Retrieved March 8, 2012.
- Dorros, A., 1989. Feel the Wind, New York, NY: Harper Collins.
- PBS Kids Go! Cyberchase. (2009). Measuring Wind Speed (Episode 704: Blowin' in the Wind). Thirteen/WNET. Retrieved February 27, 2012.
At Weather Wiz Kids you can learn all about the forces that shape the weather:
- Weather Wiz Kids. (n.d.). Wind. Retrieved March 8, 2012.
Materials and Equipment
- 5 three ounce paper cups (Dixie Cups)
- 2 soda straws
- Paper punch
- Sharp pencil with an eraser
- A fan with at least three different speeds (high, medium, and low)
- Ruler (optional)
- Take four of the paper cups and use the paper punch to punch one hole in the side of each cup, about a half inch below the rim.
- Take one of the four cups and push a soda straw through the hole. Fold the end of the straw and staple it to the side of the cup across from the hole. Repeat this procedure for another one-hole cup and the second straw.
- Take the fifth cup and punch four equally spaced holes in the side of the cup, about a quarter inch below the rim. Then punch a hole in the center of the bottom of the cup.
- Slide one cup and straw assembly through two opposite holes in the cup with four holes. Push another one-hole cup onto the end of the straw just pushed through the four-hole cup.
- Bend the straw and staple it to the one-hole cup, making certain that the cup faces the opposite direction from the first cup. Repeat this procedure using the other cup and straw assembly and the remaining one-hole cup.
- Align the four cups so that their open ends face in the same direction either clockwise or counter-clockwise around the center cup.
- Carefully push the straight pin through the two straws where they intersect.
- Push the eraser end of the pencil through the bottom hole in the center cup. Carefully push the pin into the end of the pencil eraser as far as it will go. You may need an adult to help you push the pin in.
- Now your anemometer is ready for use! It should look like Figure 1:
A homemade anemometer is made up of 5 styrofoam cups, two straws, tape, a nail and a pencil. An upright pencil serves as the base and sticks through the bottom of a stryofoam cup. 2 straws are taped into a cross and attached to the eraser of a pencil using a small nail. The ends of each straw are inserted into the sides of 4 styrofoam cups that are turned horizontally with the openings of the cup pointng in a clockwise direction.
Figure 1. When your anemometer is completely assembled, it should look like the one in this picture.
- Now set up the fan on one side of the room and mark a line with tape on the other side of the room from the fan, about 6–8 steps away.
- Turn the fan on low speed and stand on the line across the room. Hold up your anemometer and count the number of turns it makes in a minute. This is its revolutions per minute (RPM). Get someone to help you time the minute with a kitchen timer so that you can do the counting.
- If you find that the anemometer is moving too fast for you to count then you will need to increase your distance and try the experiment again. Remember, all of your data needs to be collected from the same distance for each speed, as a control.
- Repeat step 11 for the other speeds of the fan (medium and high), each time taking at least three different readings and averaging the results. You can calculate the average by adding the three readings together for a fan speed and dividing the answer by three. You should keep your data organized in a data table like Table 1.
|Fan Speed||Anemometer Revolutions per Minute (rpm)|
|1st Reading||2nd Reading||3rd Reading||Average|
- Now you need to make a graph of your data so you can analyze your results. On the left side of the graph (y-axis) put a scale for your anemometer readings in revolutions per minute. On the bottom of the graph (x-axis), put a mark for each of the different fan speeds (low, medium, high). Then draw a bar for the average reading for each of the fan speeds.
- How did your anemometer work? What happens to the number of turns of the anemometer in revolutions per minute as the wind speed increases?
Ask an Expert
- Try using your home-made anemometer to measure the wind speed outside. You can track the changes in wind speed over several days at your home. How often does the speed of the wind change where you live?
- You can also take your wind meter around town to find out if some parts of town are more windy than other parts of town. If you live near the ocean, is it windier at the beach or inland? If you live near the mountains or a tall hill, is it windier at the top or at the bottom?
- Try making other weather instruments to track weather patterns in your backyard. You can make a rain gauge to measure precipitation and a wind vane to measure wind direction. Track the weather over several days. How does your data compare to the local news forecast?
- For a more advanced project, you can calculate the speed of the wind in miles per hour (mph). Calculate the circumference of the circle made by the rotating paper cups and convert this to miles. Multiply your RPM value by the circumference of the circle in miles, multiple by 60, and you will have an approximation of the speed at which your anemometer spins (in mph). Winds of 5 mph cause leaves to rustle, while a 20 mph breeze can sway small trees. The highest wind speed ever recorded was in the Tropical Cyclone Olivia in 1996; it reached 253 mph. Your anemometer doesn't need to be pointed in the wind for use. You should be aware that some forces are being ignored including drag and friction for this elementary anemometer design, so the velocity at which your anemometer spins is not going to be exactly the same as the wind speed.
If you like this project, you might enjoy exploring these related careers: