Lesson 16: Sound and Vibrations

Sound begins with vibration. Rubber bands, humming, and a homemade harmonica connect the speed and size of vibrations with pitch and loudness.

Key Ideas

  • Sound begins when something vibrates, or moves back and forth.
  • When an object stops vibrating, it stops making new sound. Sound already made can keep traveling or echo back.
  • Faster vibrations make a higher pitch. Slower vibrations make a lower pitch.
  • For the same kind of sound, bigger vibrations usually make it louder.

Vocabulary

  • Vibration: A back-and-forth movement.
  • Frequency: How many vibrations happen in one second. Faster vibrations make a higher pitch.
  • Amplitude: How far a vibration moves from its resting position. Bigger vibrations usually make a louder sound.
  • Pitch: How high or low a sound is.

Hands-On Activity: Build a Popsicle Stick Harmonica

Supply List

  • 2 jumbo popsicle sticks
  • 1 large rubber band
  • 2 small rubber bands
  • 1 plastic straw
  • Scissors

Instructions

  • Stretch the large rubber band lengthwise around one popsicle stick so it runs the full length of the stick.
  • Cut a piece of straw about 1 inch long. Slide it under the rubber band near one end of the stick.
  • Place the second popsicle stick on top. Wrap a small rubber band tightly around that end to hold both sticks together.
  • Cut a second 1-inch piece of straw and slide it between the sticks at the other end.
  • Wrap the second small rubber band tightly around that end. Your harmonica is ready.
  • Place your lips over the large rubber band in the middle and blow gently to play.
Experiments: Move the straws closer together and compare the pitch. Then keep the straws in place and vary how gently you blow. Compare loudness and pitch rather than assuming only one will change. Frequency relates to pitch; greater wave amplitude generally sounds louder under comparable conditions.

Discussion Questions

  1. What has to happen for a sound to be produced? Can you think of something that makes sound by vibrating?
  2. Stopping a source stops it making new sound, but emitted waves can still travel or echo. What could you hear after the source stops vibrating?
  3. What is the difference between frequency and amplitude? How does each one affect the sound we hear?
  4. Can you make a sound that is high-pitched but quiet? What about low-pitched but loud? How?
  5. Imagine two guitar strings are vibrating. One vibrates very quickly but only moves a tiny amount; the other vibrates slowly but moves a lot. How would their sounds differ?
  6. What are some sounds in your environment that have a very large amplitude? What about very small amplitude?
  7. If you wanted to make a musical instrument higher-pitched without making it louder, what could you change?

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