GRADES 4-8
MAKING A MUSICAL INSTRUMENT

BACKGROUND INFORMATION: What Is Music? Why are some sounds so pleasant to hear while others are irritating noise? Music is "controlled sound", tones that have rhythm, melody or harmony, while noise can be clashing, disagreeable and harsh. Music is produced through sound waves. Different types of musical instruments control sound waves in specific ways to produce the patterns of sound we call music. Wind instruments (like the flute, recorder and trumpet) produce music differently then stringed instruments (like the guitar or piano). What Are Waves? Toss a small stone into a pool of water. Waves are formed from the point the stone hit the water. The waves form a circular pattern around this entry point and spread farther and farther apart. When you look at these waves from the side you can see the crests (high points) and troughs (low points). These Water Waves Form A Circular Pattern Click On The Picture To See Movie There are several different types of waves. Sound and light are two types of waves. To control sound, light or water waves, engineers need to understand how waves are created, behave and move. Not all waves behave in the same way. For example, light can travel through the void of outer space but sound must travel through air or some other type of material. Sound Waves Sound waves also are known as compression waves. Compression means to press or squeeze together. (The opposite of compression is expansion, to increase in size or volume.) Sound waves are produced by a series of compressions and expansions within the material it moves. An analogy (a similar situation) is the inflation and deflation of a balloon with a hand pump. When you pump air into the balloon, it quickly expands. However, the air right outside of the balloon is compressed (squeezed together) to make room for the larger balloon. That layer of air compresses the air next to it and the compression wave travels through the air away from the balloon in all directions. When you reverse the process and pump the air out of the balloon, the balloon contracts (gets smaller) and the air outside the balloon expands to fill in the space the balloon occupied. Reflection When a wave strikes a surface or moves through an area where the material's properties change, the wave will either change direction or reflect (cast) back. In a swimming pool, waves which strike the sides of the pool, reflect back. The reflected waves and original set of waves can pass through one another. In the movie below, water waves which strike the stick are reflected. The reflected waves pass through the original set of waves moving towards the shore. When a wave is moving through air and then travels into water, the wave changes direction. Wave Reflection Click On The Picture To See Movie Pitch In the picture of the pool of water you can see different size circles. These are the crests (tops) of the waves. The number of waves (or vibrations) per second is called the frequency of the wave. (Vibration means to move back and forth.) The pitch, the high or low sound of the tones, is controlled by the frequency as well. The higher the frequency (the higher the number of vibrations or waves), the higher the pitch of that sound. Musical tones have a definite frequency; noise does not. Producing Music: There are many types of musical instruments, such as the violin, tuba, flute, clarinet, piano, drum, cymbals and organ. (Can you name some others?) These instruments all produce musical sounds but in different ways. Instruments like the violin, guitar and piano have strings attached to the instrument's main body, a box-like frame. As the strings vibrate music is produced. Percussion instruments like drums and cymbals produce musical tones as their surfaces are struck. The vibrations created by these instruments move into the surrounding air. Wind instruments like the organ, flute and tuba all have air chambers. When air is blown into the tubes it vibrates producing music. One of the simplest musical instruments is a soda bottle. As you blow across the top of it, air pressure is created. The air vibrates or oscillates creating a wave, which compresses and then expands the air inside the tube. When the wave hits the end of the soda bottle it is reflected and travels back up the bottle. If you try bottles of different lengths you will notice longer bottles produce deeper sounds. The straw instrument you build in this activity acts like a woodwind instrument (a flute or recorder). The flute, piccolo and recorder all consist of a tube with a series of holes. Air is blown inside the tube, which produces a wave and a musical note. The pitch of the note depends on the length of the tube, a shorter tube produces a higher note. To create different notes the holes on the instrument are left covered or opened. Covering the holes increases the length of the tube, and leaving the holes open shortens the length of the tube. REFERENCES: Freeman, Ira M. and Durden, William J., Physics Made Simple, Doubleday, New York, 1990. Macaulay, David, The Way Things Work, Houghton Mifflin Company, Boston, 1988.