Teacher Background Information

This activity addresses NGSS Performance Expectation HS-PS4-1.

• The activities are designed for students to use empirical evidence to determine the relationships between frequency, wave speed, and wavelength, in the context of explaining the anchoring phenomenon of waves on guitar strings.

• First, students engage with the anchoring phenomenon. They observe guitar string waves and the sounds they create from Youtube videos. Then, they model their initial ideas about why guitar strings make different sounds and what causes the patterns on the strings that they observed.

• Next, students engage in a series of investigations to develop ideas they need to understand the phenomenon. They use the PhET simulation to observe wave behaviors, such as how waves invert when they reflect off the fixed end of a string. They also measure wave speed. This is helpful for understanding waves on guitar strings. It would also be helpful for students to have personal experience with a guitar or other stringed instrument.

  • Students should notice from the video that guitar strings have different properties. They are made of different materials, have different thicknesses, and have different tensions.

  • In the simulation, students can change tension of the string and observe the effects on the waves.

  • From the simulation, they will learn that the wave speed of a wave depends on the properties of the medium, so they can infer that the wave speed of a wave on a guitar string depends on the properties of the material, such as its thickness, and tension.

  • For guitars, students may need to observe a guitar being tuned to notice how tension affects pitch. Or they can conduct a simple experiment with a homemade instrument.

• Using the simulation, students manipulate frequency and observe the effects on the other wave properties. They determine the effects on these properties through their data tables and graphs. They manipulate tension and observe the effects on the wave properties. They should notice that tension does affect wavelength and wave speed through their data tables and graphs. They use the data that they collect as evidence for their causal claims.

• Students create mathematical representations of the phenomenon as they create scatterplots and then find trendlines or equations of best fit for the data. They use a Google Sheet to analyze, represent, and model their data. They determine mathematical models for the data that are evidence of relationships between frequency, wave speed, and wavelength. These models are evidence for their causal claims about relationships among wave characteristics.

• Students use their findings to create a revised model for how guitar strings make different sounds. "Look fors" in the final model include:

  • The guitar strings are different. They are made of different materials, have different thicknesses and tensions.

  • The wavelengths are different on the different strings and the strings make different sounds (lower or higher pitches). Thinner strings have higher pitch.

  • When tension increases, pitch increases and wave speed increases.

  • When the string is plucked, a wave pulse travels up the string, reflects off of the fixed end and returns.

  • For a given string, when frequency changes, wave length changes in the simulation.

  • For a guitar string, the frequency (pitch) is determined by the tension (tuning the guitar) and the kind of string. Higher tension causes higher pitch and higher wave speed. This should be observable from the data tables, graphs, and trendlines.

  • Louder sounds happen when the string is plucked harder and there is a bigger amplitude on the string. This is like moving the wrench more in the simulation.

  • Frequency does not affect wave speed. On the same string as frequency increases, wavelength decreases and wave speed stays the same. This should be observable from the data tables, graphs, and trendlines.

Examples of three-dimensional activity-level performance expectations:

• Gather data (patterns) to serve as the empirical evidence as part of building and revising models that explain how guitar strings make different sounds.

• Develop and/or use a model based on evidence to illustrate relationships (cause and effect) between the behavior of a guitar string and the sounds it makes.

• Produce data to serve as the basis for evidence as part of supporting explanations for (cause and effect) the relationship between wavelength, frequency, speed of a wave, and the properties of the guitar string.

• Analyze, represent, and model data to identify patterns that support claims about relationships between wavelength, frequency, speed of a wave, and the properties of the guitar string.