Pitch and Volume

Since we had done previous activities with sound, kids were familiar of the fact that sound waves travel through air are longitudinal waves with compression and rarefaction.  Just to brush up their memory, we reviewed some of the concepts such as 

 How the sound is produced?

Sound is produced when something vibrates. The vibrating body produces sound waves or vibrations in the medium (water, air, etc) around it to vibrate. Vibrations in air are called longitudinal waves, which we are able to hear. These sound waves have high and low pressure  areas called compression and rarefaction.

Why is the sound called longitudinal wave?

Sound waves are called longitudinal, because particles of the medium through which sound travels moves parallel to the direction of the sound waves.

Here, with the help of the  slinky it can be shown how sound waves move. To make it simple, for the kids to understand pitch and volume, the following demonstration can be done using an elastic rubber band .

Pitch and Volume

Materials needed

1. Big rubber band - 1
2. Board with a clip  -1

Procedure

1. Take a big rubber band and cut it to make it like a long string.
2. Attach one end of the rubber band to the clip on the clip board.
3. Hold the rubber band and pluck it. You will hear vibrations.
4. As you hold and stretch it harder, you will hear the pitch increase.
5. To increase the volume, you have to pull the rubber band horizontally.

vibrating rubber band when plucked

Pitch increases when the rubber band is stretched and plucked

Volume increases when it is pulled horizontally

 After some serious science concepts, time to chill out with "singing wine glasses". Yes, you read it right!

Singing wine glasses

Using wine glasses you can make a high pitched sound, by rubbing it with water. When the rubbing matches the 'resonant frequency' of the glass it would make a sharp noise.

We made it into an experiment by doing it with 3 different glasses.

Materials needed

1. Wine glasses - 3
2. Water - 1 cup
3. Rice - 1 cup


 

Procedure

1. Have 3 empty wine glasses on a table.
2. Add water in one of the cups and rice in the other one.
3. Slightly wet your fingers and rub it against the rim of the wine glass.
4. Observe the sound produced in all the three wine glasses (empty, water & rice filled).
5. Note, the change in pitch of the sound produced in each glass. 

Variations 

You can use different levels  of water (1/4, 1/2 , 3/4 cups filled) in a glass and observe the pitch changes. The more the water added, lower the pitch of the sound produced. This is due to the fact that, more the water volume, it makes the glass walls  hard to vibrate and there by produce lower pitch sound.

Find different glasses, change the water levels to produce each note of the musical scale. You can play a simple song with a your glass harp.