Sound is created by moving or vibrating objects. This vibration pushes and pulls on the air molecules close to the object, which then push and pull on the molecules next to them, which push and pull on the air molecules next to them, getting further and further from the object. This phenomenon is called a longitudinal wave (a.k.a. compression wave). A good way to visualize this is using a slinky: if you hold a slinky in mid air or lay it out on a table, and tap one end, the first coil of the slinky will push and pull on the second coil, which will push and pull on the third coil, and so on. This causes a wave that moves all the way through the slinky, even though the slinky itself does not move.
Here is a YouTube video showing the slinky demonstration, taken and uploaded by Trevor Murphy. Thanks to Mr. Murphy for sharing this excellent demonstration!
Thanks to Harvard Natural Sciences Lecture Demonstrations for producing and uploading this video!
Here’s what you’ll need:
1. A stemmed wine glass, the thinner the glass is the better.
2. A small amount of water (just enough to get your fingers wet)
Here’s what you need to do:
1. Set the wine glass on a flat surface. Hold the very bottom of the stem to keep the glass still.
2. Wet your fingers well. This allows your fingers to glide along the rim of the glass easily.
3. Slowly start running your fingers around the rim of the glass, using the part of your finger between the tip and the second knuckle.
You may have to practice a little before the wine glass begins to make sound. Keep trying!
How many notes can you make with your wine glasses? If you add water to the glasses, they will create a different note when you run your finger over the rim, depending on how much water you add. See if you can create a whole scale or play a song! With a lot of practice, you will eventually be able to play like Robert Tiso, who in the video below plays Dance of the Sugar Plum Fairy by Tchaikovsky using only glasses and water! Thanks to Robert Tiso for sharing this amazing video—ENJOY!