Who doesn’t like to listen to good music? There are songs for all tastes.
Musical sound, in general, is one that is pleasant to our ears, whose sound wave has a certain regularity. Musical instruments are devices that produce this type of sound.
Musical instruments are classified into three groups, string instruments, wind instruments and percussion instruments. How physics explains the functioning of these instruments is what we will see now.
String instruments
If we stop to think about it, we can list a large number of string instruments: guitar, violin, piano, harp, electric guitar, double bass, etc. In these instruments, sound is produced from strings, which when activated cause compressions and rarefactions in the air, called sound waves.
Also called vibrating strings, the strings of musical instruments, when vibrated, produce transverse waves that, superimposed on those reflected at the ends, originate a standing wave.
The simplest mode of string vibration characterizes its fundamental frequency, corresponding to the vibration between the string attachment ends (knots) and a midpoint. The second mode of vibration corresponds to the end nodes and a node at the center point. The third mode corresponds to one more node between the extreme nodes, and thus, each new mode of vibration corresponds to one more intermediate node.
The distance between two consecutive nodes corresponds to half a wavelength and the oscillation frequency is given by , where v is the wave velocity on the string.
vibrating strings
wind instruments
Wind instruments are made up of sound tubes. It is very easy to remember these instruments: saxophone, trombone, trumpet, flute, etc.
If you blow into a glass bottle, for example, you will notice that it emits a sound. This happens because the column of air inside the bottle vibrates, emitting a sound wave. The production of this wave at one end is due to a device called the mouthpiece. The end opposite the embouchure can be opened or closed, giving rise to two types of sound tubes, open and closed.
In open tubes, the longitudinal standing wave that forms has a belly at both ends. The simplest mode of vibration corresponds to a node at the center point of the tube. With each new mode of vibration, another intermediate node appears.
The distance between two consecutive antinodes is equal to half the wavelength and the frequency is given by: .
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open sound tubes
In closed sound tubes, the longitudinal standing wave has a belly at the end of the mouthpiece and a knot at the closed end. For each existing vibration mode, the node at the closed end is maintained and an intermediate node is increased.
The distance between the belly and the consecutive node corresponds to a quarter of the wavelength.
closed sound tubes
Percussion instruments behave very differently from other instruments. The sounds emitted by them can have their origins in the vibration of membranes, rods and metallic surfaces, which makes it difficult to establish a pattern of behavior for them.
By Kleber Cavalcante
Graduated in Physics
Team
waves – Physical –