Materials: 2 different projects to help demonstrate some of the physics of sound:
1) 12 plastic 'Easter' eggs, small items such as rice, paper clips, marbles, pennies, etc.
2) Toilet paper roll cardboard inner tube, wax paper, rubber band.

Procedure

Have one person fill each of the plastic eggs with a different item. Put some rice in one, some dried beans in another, etc. Keep track of what you put in each egg by writing numbers on the egg. Have a different person try to see if they can figure out what is inside each egg by shaking and listening to the sound generated. After taking a first guess, now show the person the list of what items are in each egg and have them guess again. See if the person changes their mind about some of the previous guesses. Now open the eggs and see how close the guesses were to what was actually inside each egg.

Now, let's make a musical instrument called a kazoo. Cut a small square of wax paper about one inch larger than the end of the cardboard tube. After doing that, wrap the wax paper over one of the ends of the tube and put a rubber band over the paper to hold it in place. Now, put the open end of your kazoo up to your mouth and hum a tune into it. Notice how the kazoo buzzes and vibrates to amplify (make louder) the sound of your voice.

What's going on?

Sound is created when the air around us gets pushed quickly (compressed) and then the push stops. This air compression produces what scientists call a sound wave. Our ears can detect that wave and through the ear's eardrum, some small bones, and some nerves, and tells our brain that a sound was just heard. Our brain can determine quickly all kinds of different sounds. Notice how just very small differences in the sound that came from the plastic eggs was just enough for you to figure out what was in each egg.

The sound of our voice seems to be made louder by humming into the kazoo because the kazoo resonates or vibrates with the sound of your voice. Your voice is a complex sound wave that contains lots of different sounds all put together so that it sounds like one sound. Scientists call the different sounds harmonics, and all those harmonics together is what makes your voice sound different than someone else's. As your voice travels down the cardboard tube and reaches the wax paper, the wax paper vibrates and all those harmonics get amplified (made louder). Not all the harmonics get amplified the same amount, so the kazoo actually changes the way your voice actually sounds. When you hum a tune into the kazoo, you get a completely different sound. Some people call this music, some call this noise.

Sound is just air that has been compressed in 'waves'. Our ears are especially good at detecting those waves (also called listening). When we hear something, our brain is able to figure out in less than a second, whether we have heard this sound before, and if not, make really good guesses at what the sound came from. Think about how we are able to do this.

We, as humans, have created many more sounds. Some of these sounds are what we would call music and the music is created in lots of different ways. Many hundreds of years ago, people found that certain things, such as a metal wire, when plucked, produced a pleasant sound. Over the years the people created many musical instruments from that simple sound. Many other musical instruments came directly from what saw and heard around them. People observed nature and learned to imitate the sound they heard. See if you can think of some musical instruments that sound like the sounds of nature.