Facilitator/Educator Guide: Measuring Wind with Your Own Wind Meter
Wind can be a very powerful force, especially at high speeds. But just how much faster is a strong wind compared to a gentle breeze? Help your students measure wind speed using a wind meter (or anemometer) they create with paper cups, straws, a pencil, and a pin.
Wind results from a difference in pressure, specifically from air molecules moving from higher to lower concentrations (high- and low-pressure areas). To measure wind speed, a wind meter (also called an anemometer) is used. Meteorologists use anemometers and other tools to predict weather based on measurements they gather from the atmosphere. A simple anemometer has four cups, with each cup attached to a single end of two horizontal arms. The arms intersect and are attached to each other in the middle, where they are both attached to a vertical rod. Each cup faces the same direction, so that when wind pushes a cup, it turns away from the wind, exposing the next cup to wind from the same direction. The anemometer's arms turn with the wind; the faster the wind, the faster the arms turn.
The anemometer in this activity measures wind as revolutions per minute (rpm), or how many times in one minute a given cup completes a full circle from where it started. However, wind speed in miles per hour (mph) or other units can also be calculated using these anemometers (see the section For Further Exploration). Winds of 5 mph cause leaves to rustle, while a 20 mph breeze can sway small trees. Winds greater than 60 mph can cause significant damage, although even winds of lesser velocity change landscapes over time. The highest wind speed ever recorded was in the Tropical Cyclone Olivia in 1996; it reached 253 mph.
In this science activity, students can make their own anemometer using paper cups, straws, a pencil, and a pin, and then use it to measure winds of varying speeds.
This science activity can serve as a starting point for a variety of science and environmental discussions. Here are a few examples of questions that can be used to start a discussion:
- What causes wind?
- Can you think of some places you have been that are windier than others, such as beaches? Why do you think these places are windier? It may help to think about how hot air rises and leaves a low-pressure vacuum that cooler air fills in.
- Do you expect the anemometer to spin faster or slower when a strong wind blows over it compared to a gentle breeze? Why?
- Come up with examples of other tools, appliances, or things that move at a given number of revolutions per minute (rpm). For example, devices in your home, in cars, or on the playground.
- What are wind turbines and what do they do?
Needed for preparing ahead:
- Three-ounce paper cups (5 per demo or small group). Dixie cups work well, though other small, lightweight cups may be used.
- Paper hole punch or sharpened pencil (1)
- Ruler or tape measure (1)
Needed for each demo or small group at the time of the science activity:
- Three-ounce paper cups (4 with one hole punched and 1 with five holes punched)
- Plastic straws (2)
- Pin (1)
- Stapler (1)
- Pencil with an eraser on one end (1)
- Fan with different speeds (optional)
- Timer (optional)
|Figure 1. You need only a few simple household materials to do this fun science activity. You can use a paper hole punch instead of a sharpened pencil to create holes in the paper cups.|
What to Do
Prepare Ahead (< 10 minutes)
- Use the paper hole punch or sharpened pencil to punch one hole in the side of each cup, about ½ inch below the rim. For each demo or small group, prepare four cups this way.
- Use the paper hole punch or sharpened pencil to punch four equally spaced holes in the sides of another cup, about ¼ inch below the rim. Then, with the pencil, punch one hole in the center of the bottom of the cup. For each demo or small group, prepare one cup this way.
Science Activity (20-30 minutes)
- Each demo or small group should have four one-hole cups, one five-hole cup, one pin, two straws, one stapler (or access to a classroom stapler), one pencil with an eraser on one end, and access to a fan (optional).
- Have students take one of the one-hole cups and push a straw through the hole about an inch. Tell students to fold the end of the straw on the inside of the cup and staple it securely to the side of the cup. Repeat this using another one-hole cup and the other straw.
|Figure 2. Have students push straws through two one-hole cups and staple the straws to the side of each cup.|
- Have students take each of their straw-cup assemblies and push the empty end of each straw straight through two facing holes on the side of the five-hole cup, to form an "X" in the middle of the five-hole cup. Make sure that the cups face the same direction, with the rims all facing either clockwise or counterclockwise.
|Figure 3. Students should take their two straw-and-cup assemblies and push the empty ends of each straw straight through two facing side holes in the five-hole cup.|
- On the empty end of each straw, tell students to insert a new one-hole cup about an inch into the cup, then fold the straw on the inside and staple it securely in place, as they did in step 2 above. Make sure that cups on the same straw face opposite directions.
- Have students position all cups an equal distance from the center of the five-hole cup and then carefully push the pin through the two straws where they intersect, roughly in the middle of the open end of the five-hole cup. You can help students push the pin in if it is safer for you to do so.
- Instruct the students to push the pencil through the hole in the bottom of the five-hole cup, eraser-end first, until it reaches the straws. Then ask the students to carefully push the pin securely into the eraser; help them push in the pin if necessary. The completely assembled anemometer should now be ready to measure wind speeds.
|Figure 4. After attaching cups on the empty ends of the straws, then pinning the two straws together and securing them to the pencil eraser in the middle of the five-hole cup, students should have a complete anemometer that is ready to measure wind speeds.|
- To have the students see how the anemometer detects wind, have them hold the meter upright on a desk or table and blow straight into an open cup. Tell them to blow gently for a few seconds, and then blow harder. How did blowing harder change how the anemometer turns? It is recommended that students sit down while doing this in case they start to feel light-headed or dizzy; in that event, instruct students to immediately stop and catch their breath.
- If a fan that has different speeds is available, have students hold their anemometer in front of the fan at different speeds. Then, they can count the number of revolutions any given cup on the anemometer makes in 15 seconds and multiply that value by four. This number will be in revolutions
per minute (rpm) as in the equation below.
Revolutions per minute = (# of revolutions in 15 seconds) × 4
How did the rpm change when the students held their anemometers in front of the fan at a slow speed compared to a faster speed?
You should see that when the students blow harder into the anemometer, or when they hold it in front of a faster speed on the fan, the anemometer turns faster. This is because the faster wind speed pushes the cups harder, making the arms turn faster. Because there is friction (where the arms and pencil connect and between the pencil and bottom hole in the five-hole cup), this homemade anemometer moves slower than a store-bought one.
For Further Exploration
This science activity can be expanded or modified in a number of ways. Here are a few options:
- What is the speed of the wind outside? Have students take their anemometers outside on a windy day, or over multiple days, to measure the wind speed.
- Are different places around the school windier than others? You can have students measure the wind speed at different locations, such as in narrow hallways or an open playing field.
- What is the actual velocity of wind, in mph, that students are measuring? To determine this, have students first calculate the circumference of the circle made by the rotating paper cups, convert this to miles, then multiply this by an rpm value. Multiply your product by 60 and you will have an approximation of the velocity at which the anemometer is spinning (in mph), although this does not take friction into account.