Introduction
On November 7, 1940, a bridge suspended over the Tacoma Narrows in Washington state was kicked up in a strong wind and began to sway and warp. The bridge was designed to move slightly up and down in the wind earning it the nickname, "Galloping Gertie." But on this particular day, the waving of the bridge resonated in a way that was not expected by the designers and the entire bridge collapsed. 

Check out this video of the collapse of the Tacoma Narrows Bridge. (http://youtu.be/j-zczJXSxnw) The resonance of waves can be a very powerful thing indeed.

In this lesson, we will learn about the basic building blocks of nearly all musical instruments, including the human voice. In the process, we will see the important role that resonance plays in generating "good vibrations."

Lesson

• We will begin this lesson with a simple activity. To complete this activity, you will need:
• A plastic cup
• A rubberband
• A plastic straw
• A pair of scissors
• Stretch the rubber band around the cup from top to bottom so that the elastic is tight across the mouth of the cup (as shown in the image at right). Pluck the rubberband so that it makes a sound. Make the rubberband stretch tighter and pluck it again. Now make it loose and play it once more. Continue to experiment in order to determine how the tension of the rubberband influences the sound it makes.
  
  
• Now, keep the tension of the rubberband constant. With your left hand, pinch the rubberband in the center and pluck either side (like in this image). Try this a few more times, pinching in different locations. Continue to experiment in order to determine how the length of the rubberband influences the sound it makes.
  
  
• Generate a summary sentence that begins with: "In order to raise the pitch of a plucked rubber band, ..." Your sentence should include two different approaches. 
  
  
• Next, we will experiment with blowing air into straws. Blow across the top of a straw and try to get it to make a sound. Now cover the other end of the straw with your finger and blow once more into the top. How does the sound change?
  
  
• Use a scissors to cut roughly one inch off of the bottom of the straw. Blow across the top again to see how to sound changed. Continue to experiment by cutting more off of the straw in order to determine how the length of the straw influences the sound it makes.
  
  
• Create a summary sentence that begins with "In order to lower the pitch of air blow through a straw,..." Your sentence should include two different approaches.
  
  
• Nearly every instrument can be simplified to either a plucked rubberband (all stringed instruments) or a straw (all woodwind and brass instruments). Watch this interesting video of an artist/musician who makes his own unique intruments out of recycled parts. As you watch, look for the connections between his instruments and the instruments we created in our simple activity. (http://bit.ly/ODXeXE)
  
  
• When any instrument plays a note, we say that it is "resonating." Every instrument has so-called natural frequencies. These are specific frequencies at which the instrument loves to vibrate. When a craftsman makes an instrument, they design it so that its natural frequencies align with the standard notes of a scale. Middle C, for example, is played when an instrument resonates at 260 Hz. So, if you wanted your rubberband guitar to play Middle C, you would need to fine-tune the tension so that its natural frequency is 260 Hz. That way, when plucked, it would resonate at that frequency and play the note.
    
• By pressing the strings on a guitar or closing the holes of a flute, the musician is changing the natural frequency of the instrument. With our straws, we changed the natural frequency by cutting the ends off. Instead, we could poke holes in the straw at various locations and then play the straw just like a recorder, covering and uncovering the holes with our fingers.
  
  
• It's not just instruments that resonate at their natural frequencies.
• A wine glass has a natural frequency. If you sing that frequency loud enough, it will resonate so much that it shatters. (http://youtu.be/Jy8js2FmGiY) 
• Buildings have natural frequencies. When earthquakes rumble near that frequency, the whole building can sway. (http://youtu.be/bX64UJpbsJI)
• And of course, a whole bridge can have a natural frequency, which we saw clearly illustrated in the Tacoma Narrows video above.

Assignment

After every few lesson in this course, we will have a brief CheckPoint Quiz covering the previous several lessons. Return to the main course page and begin the MM CheckPoint Quiz 1. 

Return to Sample Curriculum
Continue on to Lesson 4