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Sound Waves and Pressure

Investigation 2 – PreLab









Sound engineering technicians add sound to make a movie monster roar, set up the sound equipment for live concerts, and equip Broadway show actors with microphones so that the audience can hear them.


This Investigation is designed to help you to answer the following Focus Questions:

  • What is the speed of sound in air? 
  • In the same type of matter, is the speed of sound different for different frequencies and wavelengths? 
  • What is the relationship between the wavelength and frequency of a standing wave and the sound it produces? 

Note: These questions are located in your SDR at the beginning and end of the Investigation.



As a class, read the Background(s) in the Investigation. When finished, discuss the following concepts as a class:

  • The unit of frequency is the Hertz which is defined as the number of vibrations that occur in one second. Hertz are therefore expressed as 1/sec.
  • The unit of wavelength is the meter and is defined as the length of the standing wave of a vibrating object and the length of the pressure wave of the sound the vibrations produced.
  • The speed of a standing wave or a pressure wave has units of meters per second.
  • The speed of a wave, its frequency, and its wavelength are all related by the following equation: Speed = wavelength x frequency
  • The speed of sound is always the same in a specific type of matter whether the wavelength changes or the frequency changes.
  • Since there is an inverse relationship between the wavelength and frequency, a higher frequency sound has a shorter wavelength and a lower frequency sound has a longer wavelength.



The following list includes Key Terms that are introduced in the Investigation Background(s). They should be used, as appropriate, by teachers and students during everyday classroom discourse.

  • speed
  • Hertz

Note: Definitions to these terms can be found on the Introduction page to the CELL.

Note: Additional words may be bolded within the Background(s). These words are not Key Terms and are strictly emphasized for exposure at this time.


  • Complete the Prediction section in your SDR. 
    • How could you estimate the speed of sound?
    • Is the speed of a high pitched sound different from the speed of a low pitched sound?
  • During Investigation 2 they will measure the wavelength of standing waves in air made by tuning forks of specific frequencies. You will then use this data to calculate the speed of sound in air.
  • Play the video below. Remember to follow along with your SDR and make any notes that you think might be helpful in the lab.
  • After the video, divide into your lab groups to discuss strategy for the lab. For example, you may assign certain group members to perform specific functions during the lab.

Note: The purpose of the video is to allow you to anticipate the laboratory experience you will soon encounter. You should leave this PreLab session with a firm idea of what to expect and how to perform in the lab.

Note: Homework is posted below the video.


You should review the video and Investigation in preparation for the Lab.