Sound is everywhere. Music, birds singing, cars and people on the street, nearly everything around us makes some sound. But what is sound really and how is it created?
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!
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!
When objects vibrate, they tend to do so at a certain frequency; that is, they move back and forth—or oscillate—at a certain speed. This pushes and pulls on the air at a particular speed, causing the wave generated to have a certain sound. This is how a tuning fork works. A tuning fork is a two pronged, U-shaped fork that vibrates with a certain frequency (and therefore a certain sound) when struck. They produce a very consistent sound corresponding to a certain note, and thus are used by piano tuners to make sure the instrument is producing the right notes.
Just like a tuning fork, U-shaped glasses made of thin glass also tend to vibrate at a certain frequency, depending on whether they contain any liquid. A wine glass is an excellent example; tap a wine glass gently with your finger, and it will usually produce a ringing sound. This is caused by the vibration of the glass, and corresponds to a certain note just like the tuning fork. In fact, if you play this note at the wine glass loudly enough, the glass will vibrate so hard it will shatter! Here is another YouTube video demonstrating this phenomenon, which we don’t recommend you try at home!
Thanks to Harvard Natural Sciences Lecture Demonstrations for producing and uploading this video!
Thanks to Harvard Natural Sciences Lecture Demonstrations for producing and uploading this video!
While you shouldn’t try to shatter glass at home, there is another way you can experience the vibration of a wine glass using your finger and a little water. This will cause the glass to oscillate at a particular frequency, creating a certain note.
TRY IT!!
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!
CHALLENGE YOURSELF!
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!
TRY IT!!
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!
CHALLENGE YOURSELF!
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!
