Make an Anemometer to Measure Wind Speed

Background Information for Teachers

An anemometer is an instrument that is used to measure wind speed. There are several different types of anemometers. A cup anemometer has three or four cups mounted about a vertical axis that can spin (Figure 1). The cups are aligned so they all face the same direction around a circle (all clockwise or all counterclockwise). The open sides of the cups "catch" the wind more than the closed sides. This means that when the wind blows, it pushes on one side of the anemometer harder, causing it to spin. The anemometer's rotation speed can then be used to determine the wind's speed. Real anemometers are calibrated, meaning that a certain rotation speed corresponds to a known wind speed. They usually display the wind speed in miles per hour (mph) or kilometers per hour (kph). In this project, your students will count how many rotations their anemometer makes in 15 seconds, but it is not possible to easily convert to wind speed in miles or kilometers per hour with this simplified anemometer. Look in the Variations section to see how students can correlate their data with real wind speeds.

Image Credit: wikimedia user Sean Linehan / Public Domain
Figure 1. A cup anemometer.

Wind is just one aspect of the weather. Meteorologists use anemometers, along with other instruments like thermometers (to measure temperature) and barometers (to measure pressure) to make observations of the weather. Studying weather patterns helps them develop forecast models to predict future weather. You probably see these forecasts almost every day when you check the weather on TV or online. In this project, your students will be meteorologists for a day by building simple anemometers with readily available materials, and measuring how changing the speed of the "wind" (using a fan) affects the anemometer's rotation speed.

Additional Background Links

• Wind, Weather WizKids

Prep Work (5 minutes)

Optional: if you do not have enough hole punchers for the class to share, you can punch holes in all the cups in advance. See steps 1 and 3 in the Explore section.

Engage (5 minutes)

Is it windy outside today? Is it windy enough to fly a kite? How could you find out if it will be windy tomorrow?

Why is it important to be able to predict the wind and other parts of the weather like the temperature or rain?

Predicting weather—if it will be hot or cold, sunny or rainy—- helps us know how we should get dressed in the morning. Predicting the wind is important because while a light breeze might be refreshing, strong winds can knock down tree branches and power lines and cause damage to buildings. Predicting high winds in advance can give people time to prepare by securing loose objects, postponing activities like going out on a small boat or riding a bike, or moving to a safer area if the winds will be dangerously high.

How can we predict the weather using our senses? Are there reliable patterns in the weather that make it easier to predict?

Students might be familiar with different weather patterns depending on your geographic region. For example, if you feel a strong wind coming off the ocean, that might mean it is going to be a colder day. If you see lots of dark clouds outside, that might mean it is going to rain soon.

Who are the people who study the weather for their jobs? How do they study the weather and how do they make predictions?

People who study the weather are called meteorologists. They gather data using a variety of scientific instruments that measure aspects of the weather like temperature, rainfall, cloudiness, and wind. Based on their observations, they can find patterns in the weather that help them predict future weather.

Can anyone name an instrument used to measure part of the weather?

Most people are familiar with thermometers—instruments used to measure temperature. In this project you will build an anemometer (pronounced an-uh-MOM-uh-ter), an instrument used to measure wind speed. We will use a fan to create wind in a controlled manner so we can do an experiment.

Explore (30 minutes)

Build The Anemometer

Walk your class through these steps so each group can build an anemometer. The assembly video also gives you step-by-step instructions for building an anemometer.

https://www.youtube.com/watch?v=Af0LB3abBsk

1. Use a hole punch or the tip of a sharpened pencil to punch four holes in a paper cup just below the rim, forming a "+" shape (two pairs of holes opposite each other).
2. Press two straws through the holes as shown in Figure 2.

Image Credit: Ben Finio, Science Buddies / Science Buddies
Figure 2. Cup with straws inserted through holes.

3. Use a sharpened pencil to poke a hole in the center of the bottom of the cup, as shown in Figure 3.

Image Credit: Ben Finio, Science Buddies / Science Buddies
Figure 3. Hole in bottom of cup.

4. Use the hole punch or pencil to punch two adjacent holes in each of the other four cups. The holes should be about 2–3 cm apart, and about halfway along the cup's height, as shown in Figure 4.
5. Push the end of a straw through the two holes in each one of the cups, as shown in Figure 4. Make sure the cups are all facing in the same direction (all clockwise or all counterclockwise). There should be enough friction to hold the cups in place so they do not twist on the straws. If the cups twist easily, use a bit of tape to secure them.

Image Credit: Ben Finio, Science Buddies / Science Buddies
Figure 4. Cups mounted to anemometer arms.

6. Push the pencil, eraser end first, through the hole in the bottom of the central cup.
7. Press a pushpin lightly through both of the straws and into the eraser, as shown in Figure 5. Do not press the pushpin into the eraser all the way, or there will be too much friction and your anemometer will not spin.

Image Credit: Ben Finio, Science Buddies / Science Buddies
Figure 5. Straws attached to eraser with pushpin.

8. Use a marker to draw an easily recognizable symbol (for example, a dark circle or band) on the side of one of the cups, so you can easily tell it apart from the other cups. This will make it easier to count revolutions when the anemometer is spinning.

Test The Anemometer

Let each group test their anemometer with the fan (multiple groups can test at a time if you have more than one fan).

1. Assign roles to each student in a group. For example, for groups of three, one person can hold the anemometer, one person can operate the stopwatch, and one person can count rotations.
2. Set the fan's speed to low.
3. Hold the anemometer about 1 foot (ft) in front of the fan. You may need to adjust this distance depending on the strength of your fan.

   Why does the anemometer spin? Why does it spin in one direction and not the other way?

   The anemometer spins because the open sides of the cups catch the wind more than the closed sides. Since the cups all face the same direction around a circle, they "catch" more wind on one side than the other, causing the anemometer to spin. You can feel this effect if you stick your hand out a car window or while you are riding your bike. If you form a cup with your hand facing the wind, you will feel a bigger push.

4. Using the stopwatch, count how many complete rotations the anemometer makes in 15 seconds by watching how many times the marked cup passes in front of you.
5. Record the number of rotations in the table on the Student worksheet.

   What do you think will happen if we set the fan to a higher speed?

   If we set the fan to a higher speed, the air will push on the anemometer harder, and make it spin faster.

6. Repeat steps 3–5 with the fan's speed set to medium and high. Record all your results in the student worksheet. It is important to hold the anemometer the same distance from the fan for each test.
7. Make a bar graph of your data on the student worksheet.

Reflect (5 minutes)

Discuss the following questions as a class.

How does the anemometer's rotation speed change when you change the fan speed? Based on the pattern you observed, what do you think would happen if you could turn the fan's speed up even higher? What would happen if you took the anemometer outside on a windy day or a calm day?

You should have observed the pattern that when the fan's speed increases, the anemometer's rotation speed increases. Therefore, if you could turn the fan speed up even higher, you would expect the anemometer to spin faster. If you took the anemometer outside on a windy day, you would expect it to spin fast. If you took it outside on a calm day, you would expect it to spin slowly or not at all.

What are some other real-life uses of anemometers?

Here are just a few examples—can your students think of more? Anemometers are used at airports so pilots know when it is safe for planes to take off and land. Engineers use anemometers to find places with consistent high wind speeds, so they know where to build wind farms to convert wind into electricity. Meteorologists use anemometers to measure wind speeds and predict how fast an approaching storm will get here.

Assess

You can use this quiz to assess student learning after the activity:

• Online quiz, assignable in any LMS
• Quiz (pdf) and answer key (pdf)

Make Career Connections

Discussing or reading about these careers can help students make important connections between the in-class lesson and STEM job opportunities in the real world.

Meteorologist

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Career Profile

Meteorologists are people who study the weather and make weather forecasts. They use a variety of scientific instruments to measure and record the weather, including weather stations on the ground (which contain instruments like anemometers) and even satellite images from space. Read more

Wind Energy Engineer

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Career Profile

Wind energy engineers analyze wind speed and direction to determine the best places to put wind farms that harvest the wind's energy and convert it to electricity using wind turbines. Read more

Lesson Plan Variations

• Try building anemometers with different numbers of cups. Does the device still work if it only has two cups? What about three, five, or six?
• Turn this into an engineering design project. Let your students use different materials, like wooden skewers or popsicle sticks instead of straws, or cut their own cups out of construction paper. Do some anemometers work better than others? Do they all spin at the same speed for the same fan setting?
• Try using the anemometer at different distances from the fan. How does the anemometer's rotation speed change as you get farther away from the fan? What does this tell you about the strength of the wind?
• Have your class take the anemometers outside. Collect data in different places, for example different locations on the playground. Are wind speeds the same everywhere? Are they affected by obstructions like buildings or trees?
• Take the anemometer to the same place outside at different times of day. Measure how wind changes over time, and see if you can detect patterns. Is the wind usually faster or slower at certain times of day? Does it relate to other weather factors you can observe, for example temperature or the presence of clouds?
• Use the wind meter as part of a weather station. Other instruments you can use include a thermometer to measure temperature, a barometer to measure air pressure, and a rain gauge to measure rainfall amounts.
• Use a digital anemometer (available from Amazon.com) to create a calibration curve for your hand-made anemometer. Take both anemometers outside on a windy day and measure the actual wind speed in miles per hour (mph) or kilometers per hour (kph) with the digital anemometer and the number of revolutions per minute (RPM) for your hand-made anemometer. Take measurements at several different wind speeds (you may need to do this in different locations or on different days). Then, create a graph with actual wind speed on one axis and revolutions per minute on the other axis. In the future, you can use this graph to convert RPM from your hand-made anemometer to wind speed in mph or kph. Note that if you purchase a fan-type digital anemometer (it looks like a miniature battery-powered fan), you will need to hold it facing directly into the wind in order to get a proper reading. This is different from a cup-type anemometer like the one you built, which works in any direction.