Use a balloon to discover how sound is created
Discovery Place Science
Ever wonder what makes sound? Well, you can answer that question with the help of an ordinary balloon!
The sounds we hear are caused by waves as air vibrates. These aren’t the same as the waves that form in the ocean. Ocean waves are caused by transverse waves and go up and down. Sound waves are a different type of wave known as longitudinal, or compression, waves.
These waves form when vibrations cause a chain reaction of compressed molecules to move through a substance. You can see what this looks like by stretching out a spring across the floor. If you squeeze some of the coils together and then release them, you will see the wave of compressed coils bounce back and forth across the spring.
When sound waves reach our ears, the vibrations of our eardrums cause us to hear the sounds. The speed of the vibrations is also known as frequency. Changes to the frequency make a sound go up or down in pitch.
Now that you know that all sound is caused by vibrations, try to create your own vibrations using different objects in your house.
This experiment includes about five minutes of preparation and approximately 15-20 minutes of learning time. It is perfect for students in third through fifth grade.
- Small objects that fit in a balloon. Examples include a marble, different shaped wooden and plastic beads, metal hex nuts, different shaped pasta, dried beans and small rocks.
1. Place the objects one at a time inside a balloon and then blow it up. If you want to reuse the same balloon, try twisting the top and securing it with a clothespin or binder clip instead of tying it into a knot.
2. Once the balloon is sealed, hold it at the top like you would hold a bowling ball.
3. Swirl the balloon in a circular motion so the object inside starts to roll around inside the balloon. Some of the objects may bounce around at first but if they are round, they should start to roll eventually. Listen to the sounds created by the various objects. Can you hear a difference in pitch being created? Do any of your objects make no sound at all? Remember that sound can only be created if there are vibrations. Try rubbing your finger along the side of the balloon, can you feel the vibrations and hear the sound? Record your observations in a table like this one:
Some objects, like a marble, may be too smooth and round to generate friction. If there is no friction on the sides of the balloon there will be no vibrations and no sound. In contrast, objects like the hex nut and the square bead have flat edges that create friction as they slide against the inside of the balloon. This causes vibrations that create sound.
Have fun seeing what kinds of sounds you can make!
How to adjust for younger and older learners:
For younger learners, ask them to draw a picture and think about what sounds the things in their picture might make. Ask them to describe the sounds.
For older learners, have them find other things around your home (inside and outside) that make sounds and describe what is vibrating to make that sound. See if they can find a pattern between things that vibrate to make a high-pitched (squealing) sound and those that make more of a low (booming) sound.
Want to experiment even more with sound? Check out our Science of Sound video here.