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Good Vibrations (Simple Physics/Sound)

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  • Do you play a musical instrument? Does someone you know play an instrument? It doesn't matter if it's a flute or a piano or a guitar, all musical instruments work because of one simple scientific principle; they vibrate. Vibrations happen anytime something moves back and forth really fast. You can feel vibrations when you speak. Gently rest two fingers on that little lump on your throat and hum. That buzzing sound you feel in your fingers are the vibrations in your vocal cords. The faster the vibrations, the higher the pitch of the sound. So if all musical instruments work on vibrations, why do they sound different from each other?

    I've got a challenge for you that lets you explore the relationship between vibrations and pitch.

    Here's what you'll need to play along:

    • 3 clean empty glass bottles all the exact same size
      (It's best if you use bottles from the same brand of drink so that there is as little difference between the bottles as possible. Also, try to get bottles with a narrow hole at the top.)
    • a metal teaspoon
    • a sink

    Begin by filling each bottle with a different amount of cold water. Fill the first bottle about 1/3 full, the second bottle 1/2 full and the third bottle 2/3 full.

    Okay, so here's the challenge question:

    Which bottle will make the highest sound when you blow in it, and which will make the highest sound when you tap it with the spoon? Maybe all the bottles will sound the same? Predict before you give it a try!

    What You Do

    Now, before you tap the bottles or blow across the top of them, guess which bottle will make the highest sound and which one will make the lowest sound.

    Here are the rules to follow after you've made your predictions:

    1. Blow across the top of each bottle as if you were blowing across a straw. Listen to the sound each makes.

    2. Gently tap on the side of each bottle with the metal spoon and listen to the sounds they make.

    3. To make sure your results are accurate, try the experiment 2 or 3 times.

    See if you can figure out why you got the results you did. Also, see if you get the same results using warm water instead of cold. Good luck, have fun and watch out for the DIRT!

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    Notes to Teachers

    Curriculum Focus: Science/Simple Physics/Sound

    Learning outcomes:

  • Experiment with and record the results made by blowing across and tapping 3 glass drink bottles containing different amounts of water.
  • Use observations from an experiment to develop a hypothesis as to why different sounds result from different situations.
  • Recognize that the pitch of a sound is controlled by the speed of the vibrations which create it.

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    Related Web Sites

    For more information about vibrations and musical instruments, try these Web sites:

    What Makes Music?

    Activities Which Teach: The Key Science Concept - Perception

    General Science Sites

    Science and Technology for Children Curriculum

    The Natural History Museum (London)

    Edison National Historic Site

    Endangered Species Program

    National Inventors Hall of Fame

    Understanding Our Planet Through Chemistry

    Maps and References

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