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This lesson aligns with NGSS PS4.A

Consider the multitude of sounds that reach your ears daily. Indoor, one may encounter the voices of people conversing, the blaring of a radio, or the clattering of dishes in the kitchen sink. Outdoor, the melodies of birds singing, the passing of cars, or the faint buzzing of bees near your ear may be audible. Despite their individuality, all sounds share some common characteristics. One such characteristic is that sound originates from vibrations. A vibration can be defined as the complete back-and-forth motion of an object. In this article, we will explore what is sound, and how sound is produced.

What is Sound?
Sound is a type of energy or vibration that propagates through various mediums, including air or water. It can even travel through gaseous substances. It is characterized by its ability to be heard by the human ear. 

How sound is produced?
It is created when an object vibrates, setting particles in the medium into motion. These vibrating particles then transfer the energy of the sound wave from one particle to another. As a result, the wave propagates and eventually reaches our ears.

When the speaker cone moves in a forward direction, it exerts a force on the air particles in front of it, causing them to compress and come closer together. This creates a region of higher density and pressure called compression.

When the speaker cone moves in a backward direction, air particles in front of it become less crowded. This creates a region of lower density and pressure called rarefaction.

Every time the speaker cone vibrates, both compression and rarefaction occur. These alternating patterns of compressions and rarefactions propagate outward from the speaker, and sound is transmitted through the air.

Sound Travels as Longitudinal Waves
A wave refers to a disturbance that transfers energy through matter or space. In the case of a longitudinal wave, particles undergo back-and-forth vibrations along the direction of wave propagation. Longitudinal waves consist of alternation patterns of compressions and rarefactions.

Sound is transmitted through particle vibrations and collisions within matter, such as air particles. As the particles oscillate along the paths traversed by sound, sound travels as longitudinal waves.

However, it is important to note that air or other substance does not travel with sound waves. The particles of air solely vibrate back and forth in place. if the air were to move with the sound, wind gusts from the music’s speaker would be strong enough to topple you at a school dance.

Sound Waves Require a Medium
Another attribute of sound is that all sound waves require a medium. A medium is a substance that enables the propagation of waves. For example, when a tree falls and hits the ground, the tree and the ground vibrate. These vibrations produce compressions and rarefactions in the surrounding air. As a result, the sound is heard.

In this example, air serves as the medium. Most sounds we hear in our daily routine travel through the air, at least partially. However, sound waves can also travel through other materials such as water, glass, and metal.

If a tree fell in a vacuum, no sound would be generated because in a vacuum there are no air particles to vibrate. Sound cannot propagate in the absence of a medium. For sound to reach your ears and be detected, it must travel through the air or another suitable medium.

How does the Human Ear Work?

Outer Ear
The out-ear functions as a funnel, channeling sound waves. The pinna specifically gathers sound waves and guides them into the ear canal.

Middle Ear
Within the middle ear, a set o three bones namely the hammer, anvil, and stirrup, functions as levers to amplify the magnitude of vibrations.

Inner Ear
The inner ear is where sound-induced vibrations transform into electrical signals, which are then interpreted by the brain.

  • A sound is a form of energy produced by vibrations that travel through a medium, typically in air or water. 
  • Longitudinal waves consist of alternation patterns of compressions and rarefactions. 
  • Sound is transmitted through particle vibrations and collisions within matter. As these particles oscillate along the paths, sound travels as longitudinal waves.
  • All sound waves require a suitable medium to propagate such as air, water, or glass.

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