Grade 8 Science : Sound - Part 1

Sound is produced by vibrations that travel through air or other medium and it can be heard when they reach our ears. For an instance, when a drum is struck, the object vibrates and that vibration produces sound. Several musical instruments are utilized to produce sound in different ways and they are called sources of sound.

These sources can be classified according to the parts that are subjected to vibration in the production of sound.

• Vibrating membranes - Examples : Base Drums, Thabla, Snare Drum, Congo Drums
• Vibrating strings or bars - Examples : Violin, Harp, Guitar, Double bass, Sitar
• Vibrating air columns Examples - :  Horn, Tuba, Flute, Clarinet, Saxophone, Trumpet, Trombone

 

Sound sources can be classified in to natural and artificial / man-made sounds. Both natural and artificial sounds are also produced through the vibration of strings or bars, membranes or air columns as listed above. Natural Sounds occur naturally and we can hear plenty of these sounds in our environment. Examples: birds call, cats mew, humming of bees, sounds of grasshoppers, wind, flowing streams/rivers, volcanoes, thunderstorms, ocean sounds and rain sounds. Furthermore, the man-made/ artificial sources of sounds are airplanes, explosions, factories, electronic appliances, vehicles, trains and etc.

Frequency of vibrations

When sound is created, the source object/instrument, the molecules in air or other medium and the eardrum are subjected to vibration. Frequency can be cited as the number of vibrations of a sound source that occur per second. Frequency is measured in Hertz (the international unit of frequency).  That is 1 unit of Hertz (1 Hz) is equal to 1 vibration per second. For example, if a source object vibrates 70 times per second, the frequency of that source object is 70 Hz. It should be noted that human beings cannot hear sounds of all frequency ranges. This is different in the case of some animals. The limited frequency range of sound that humans can hear is 20 Hz – 20 000 Hz. There exist mechanisms to change the frequency in every musical instrument and it is the manipulation of frequency that leads to the production of the seven notes in music.

 

 

 

 

 

 

 

by Mekhala Egodawele

Photo source : Internet