The Singing Glass

This is a fun and easy science experiment.  The purpose of the experiment is to show how friction can cause a glass to vibrate.

Materials:  stemmed glassware (thinner glass is better)
                 dish detergent
                 vinegar
                 small shallow bowl

Procedure:

1. Use the dish detergent to wash the glass and your hands.  Rinse well.
2. Place the glass on a table.
3. Pour a thin layer of vinegar into the small bowl.
4. Hold the base of the glass against the table with your hand.
5. Wet the index finger of your free hand with vinegar and gently rub your wet finger around the rim of the glass.

Results:  The glass starts to sing when its rim is rubbed.

Why?  Washing the glass and your hands removes any oil that might act as a lubricant.  The vinegar dissolves any oil that might be present and increases the friction between your skin and the glass.  Rubbing your finger around the rim causes the glass to vibrate because your finger skips and pulls at the glass.  The air inside the glass is struck by the vibrating glass and begins to move back and forth in rhythm with the glass.  The pitch of the sound you hear is due to frequency (number of vibrations per second).  It's all pretty cool.

What good is posting a singing glass experiment without linking a video of C actually performing the experiment?!  Check this out:

If you are reading this via email or in a reader, you will have to click through and view the video on my blog.  Come on, you know you want to see this.  C's reaction to the singing glass makes it all worth it.  It's a short video too, less than thirty seconds.

I found this experiment in the book, Physics for Every Kid by Janice VanCleave.

I am linking this post to Science Sunday at Adventures in Mommydom.  Click on over there to find more great science experiments.