An anemometer is a tool that measures wind speed, and you can build a simple one with cups, straws, a pin, and a pencil. In this school project, wind pushes on the cups and makes the crossed straws spin like a pinwheel. Marking one cup with a bright dot helps you count each full rotation.
This makes invisible moving air easier to observe and measure.
Key Facts
- Wind speed tells how fast air is moving past a place.
- One full rotation happens when the marked cup returns to its starting position.
- Rotations per second = rotations counted ÷ time in seconds.
- For a 30 second test, rotations per second = rotations counted ÷ 30.
- More rotations in the same time usually means stronger wind.
- The Beaufort scale describes wind from calm air at 0 to hurricane force at 12.
Vocabulary
- Anemometer
- An anemometer is an instrument used to measure wind speed.
- Rotation
- A rotation is one complete turn around a center point.
- Wind speed
- Wind speed is how fast air moves from one place to another.
- Beaufort scale
- The Beaufort scale is a numbered scale that describes wind strength by its effects on land or water.
- Friction
- Friction is a force that resists motion when surfaces rub or press against each other.
Common Mistakes to Avoid
- Counting every cup as one rotation is wrong because a full rotation happens only when the marked cup returns to the same position.
- Pushing the pin in too tightly is wrong because extra friction can stop the straws from spinning freely.
- Using cups that face different directions is wrong because the wind will not push the anemometer evenly around in a circle.
- Measuring for different amounts of time is wrong because counts must be compared using the same time interval, such as 30 seconds.
Practice Questions
- 1 Your anemometer makes 45 rotations in 30 seconds. What is its rotation rate in rotations per second?
- 2 In one test, the marked cup makes 72 rotations in 30 seconds. In another test, it makes 48 rotations in 30 seconds. How many more rotations per second happened in the first test?
- 3 A student says the wind speed doubled because the anemometer looked like it spun much faster. Explain why counting rotations for a set time gives better evidence than just watching it.