The Science of Sound

What is sound, and how are its characteristics explained scientifically?

Know (knowledge):

• The science of sound as a phenomenon
• The physical properties and behavior of sound waves
• The difference between longitudinal and transverse waves
• The role of compression and rarefaction in wave mechanics

Mastery Objective:

• Students will be able to explain the science behind sound waves by conducting hands-on activities.

In this lesson, students will analyze video clips of musicians playing various instruments in order to identify how sound is created. They then conduct three hands-on activities to gain a deeper understanding of the science of sound: the physical characteristics of sound, and how sound is scientifically explained and represented.

Sound is vibration. When a drum is struck, a string plucked, or any other object is moved in some way, it vibrates. These vibrations displace the surrounding air molecules, which in turn displace more air molecules, creating a chain reaction which eventually reaches the ear and/or body and is perceived as sound.

But these vibrations do not create a uniform, continuous trajectory of air molecules. Rather, the back-and-forth motion of a vibrating object creates waves of sound, where air molecules bunch together and expand out at a regular rate. This type of movement occurs in what is called a longitudinal wave, which moves via compression (when molecules are bunched together) and rarefaction (when molecules are spread apart).

While sound waves carry the characteristics of longitudinal waves, they are usually visually represented as transverse waves. Rather than staying parallel to the wave motion, transverse waves move perpendicular to the wave motion. In other words, transverse waves move up and down, creating hills and valleys, like waves in the sea. Representing sound waves as transverse waves rather than longitudinal waves allows their characteristics to be better observed, analyzed, and calculated.

• 2 medium sized bowls
• Plastic wrap
• A metal coil, such as a Slinky®
• 1 cup of sugar, salt, or sand
• A tuning fork (the larger the better)
• A large baking pan
• A large wooden spoon
• Water
• A small piece of string or yarn

1. Create the following stations where students will conduct activities related to sound waves:
   1. Station 1: Drum/Vibrating Membrane Activity
      1. Tightly cover the plastic wrap over the top of the bowl. Place a spoon and cup of salt, sugar, or sand next to the bowl.
      2. Provide copies of Handout - Drum/Vibrating Membrane Activity at the station.
   2. Station 2: Coil Spring Wave Simulation
      1. Tie a short piece of string or yarn approximately in the middle of the metal coil.
      2. Provide copies of Handout - Coil Spring Wave Simulation Activity at the station.
   3. Station 3: Tuning Fork and Water Activity
      1. Fill a medium bowl with water, and place the tuning fork next to the bowl.
      2. Provide copies of Handout - Water and Tuning Fork Activity at the station.