How do guitar strings make different sounds?

Link to a web-based version

(A series of activities for High School Physics)

Anchoring Phenomenon

  • How are different sounds on a guitar created?
  • What do guitar strings look like when a guitar is being played?

Watch this video and observe the phenomenon.

  • What patterns do you notice in the video?
    • What do the patterns on the strings look like as they are being played?
    • Do you notice any relationships between the patterns of what you hear and what you see?
  • What do you think causes those patterns?
  • Create a model to record your ideas using this Google Jamboard.

In the following series of investigations, we will use a simulation to investigate waves on strings and figure out how and why different patterns are formed on strings. Then we will use what we have learned to explain patterns that we noticed in the video.

Investigation 1 – What happens when you pluck a guitar string?

Go to the Waves on a String Simulation. Use this Google Doc to record your answers.

Instructions

  1. Set the damping to NONE with the slider.
  2. Wiggling the wrench is like plucking the guitar string. Wiggle the wrench to create a single pulse on the top side of the string.  Draw your observations of this pulse as it travels to the fixed end and back.
  3. Wiggle the wrench to create a single pulse on the bottom side of the string.  Draw your observations of this pulse at it travels to the fixed end and back.
  4. Describe any similarities or differences between the two cases you have just observed.
  5. Reduce the tension to “Low” and send another pulse.  Describe the differences between this pulse and the previous one.
  6. Change to “loose end” and repeat steps 3 and 4.  Draw what you observe for this case.
  7. Compare your observations of the loose end case to the fixed end case. 
  8. Change to “no end” and send a pulse down the string.  Draw what you observe for this case.
  9. Compare your observations of this case to the “loose end” case.
  10. Summarize your observations.
  • A wave pulse will flip upside down (invert) when it reflects off of ____________________________________________________.
  • A wave pulse will not flip upside down (remain upright when it reflects off of _______________________________________________.
  • Changing the tension in the string changes the waveʻs ______________________.

11. How does this help us explain what we saw on the guitar strings? Do guitar strings have fixed or loose ends? Update your Google Jamboard model with any new information that helps you explain the anchoring phenomenon.



Investigation 2 – Why are the shapes of waves on guitar strings different?

We are going to examine the factors that affect the shapes of waves on guitar strings using the simulation.

Instructions

12. Change to “oscillate” to produce a continuous stream of pulses.  Check the “rulers” box and the “timer” box.  

Vocabulary. Frequency is how many vibrations or oscillations per second. Wavelength is the distance between two consecutive identical parts of a wave. For example, the distance from crest to crest or from trough to trough.

  • Do not change the amplitude or tension settings until #16.  
  • Use the ruler to measure the wavelength of your wave (the distance from crest to crest).
  • For five different frequencies, measure the wavelength of the wave produced.  Record the frequencies and wavelengths in a table below:
  • Record your tension setting ________
TrialFrequency (Hz)Wavelength (m)Wave Speed (m/s)
1
2
3
4
5
Data Table

13. Multiplying frequency and wavelength to calculate wave speed. 

v = f λ

Calculate the wave speed for each trial.  Record these values in your table.

14. What is the relationship between frequency and wavelength? 

Create a graph of wavelength vs. frequency using the first tab on the Google Sheets template

Enter your own data in the template. Find an algebraic relationship (equation) that relates wavelength and frequency using the trend line function.  Insert a screenshot of your graph and its trend line.

15. What is the relationship between wave speed and frequency? 

Create a graph of wave speed vs. frequency using second tab on the Google sheets template.

Find an equation that relates wavelength and frequency using the trend line function.  Insert a screenshot of your graph and its trend line.

16. Repeat this experiment for a different string tension.  Summarize your results.  Make a claim about how tension affects wave speed based on your data and graphs. Insert a screenshot of your graph and its trend line.

New tension = _________

TrialFrequency (Hz)Wavelength (m)Wave Speed (m/s)
1
2
3
4
5
Data Table

Amplitude is the farthest that the string moves from the original position. It is the height of the crest of the wave.

17. Repeat this experiment for a different amplitude and the same tension used previously.  Summarize your results.  Make a claim about how amplitude affects wave speed based on your data. Insert a screenshot of your graph and its trend line.

TrialFrequency (Hz)Wavelength (m)Wave Speed (m/s)
1
2
3
4
5
Data Table

Revising your model of the anchoring phenomenon

18. How does this help you explain what you saw on the guitar strings? Can you explain the patterns in wavelength, frequency, and amplitude you noticed in the video?

Update your Google Jamboard model with any new information that helps you explain the anchoring phenomenon.

Think about:

  • How are the patterns on the strings in the simulation similar to or different from guitar strings?
    • Do you notice any relationships between the patterns?
  • What do you think causes the patterns on guitar strings?
    • How are the guitar strings similar to or different from each other?
    • How does the string affect the waves on the string?
  • Update your Google Jamboard model using what you have learned in the investigations to explain how and why different strings produce different sounds and how the wave patterns are related to the sounds. Use wavelength, frequency, amplitude, wave speed, and tension in your explanation.

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