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The speed of sound was first measured in the 17th century, but it remains something to marvel at. This is because of the way that the speed of sound is related to the density of material that it is passing through. Here are some nice ways to understand this phenomena.

Project 1

• 12 plastic ‘Easter’ eggs
• Small items such as rice, paper clips, marbles, pennies, etc.

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. 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, show the person the list of items that 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.

Project 2

• Toilet paper roll or cardboard inner tube
• Wax paper
• Rubber band

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 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 of 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 the 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.