This week's experiment is based on a question about sound that was sent to me by Carol in Highland Park, NJ and her Cousins from New York City.
To try it, you will need:
- three identical glass bottles
- some water
- a spoonl
Fill all three bottles about half full of water. Make sure that the water level is the same in all three. Place them on the table, and gently tap one with the spoon. It makes a nice tone. When you tap the bottle, you cause the bottle to vibrate. That causes the air around the bottle to vibrate, and as the vibrations in the air reach your ear, they cause your ear drum to vibrate, and you hear a sound.
If you tap all three bottles, you should hear the same tone from each. Now, to make this easier, lets label the bottles, 1, 2, and 3. We will leave bottle 2 just as it is, but we will pour some of the water from bottle 1 into bottle 3, giving us 1 with a low water level, 2 with the same level we started with, and 3 with a higher water level. Now tap each bottle and listen to the sound.
Bottle 1 now makes a tone with a higher pitch, and bottle 3 makes a sound with a lower pitch. Why?
When you tap the bottle, the glass and the water will both vibrate. Adding more water means that you have more mass vibrating. By adding water, we add mass. That will cause the object to vibrate slower, which means a lower tone. Removing water means less mass to vibrate, which lets the object vibrate faster, giving us a higher tone.
Now for the question. We can also make sounds by blowing across the top of the bottle. Blow across the top of bottle 2, and listen to the tone. Will the different water level in bottles 1 and 3 cause the tones to be different if you blow across them? If so, which will have a tone with a higher pitch, and which will have a lower pitch? Most importantly, why?
Well, you have a week to try the experiment, and think about your answer. Until then, have a wonder-filled week.
