Sound is defined as vibrations travelling through a medium, such as solid, liquid, or gas. When the medium vibrates, the particles inside generate movement, which we refer to as sound waves. The sound wave will then travel until it runs out of energy and dissipates. If you are within range of the vibrations, you can hear the sound produced.
For many, sound may be a difficult concept to understand, even though we encounter it daily. To better understand how sound impacts our daily lives, let us explore how it is produced, specifically in guitars and medical scans.
How is a sound produced?
In a guitar, there are six strings of different thickness. When a string is plucked, vibrations travel in the air. These vibrations travel in two ways; firstly, from the bridge to the top of the guitar, and secondly, from the side to the back of the guitar through the air inside the sound hole.
In medical scans, ultrasound tests are a safe option often used to monitor a fetus or diagnose diseases without harmful radiation. Ultrasound waves are high-frequency sound waves that the human ear cannot perceive. During an ultrasound test, a transducer is placed against a part of the body, such as the mother’s womb. Similar to the concept of echolocation, the sound waves bounce off an object, such as bones, tissues, or fluid, and are reflected back to the transducer. These waves are then recorded and displayed by a computer, creating a real-time image on its monitor.
Where can we observe the processes of compression and rarefaction?
Sound waves are longitudinal waves composed of compressions and rarefactions. Compressions are high-pressure areas where the molecules are closely packed together. In contrast, rarefactions are areas of low pressure where the molecules are more spread apart.
The vibrating object in a guitar would be its strings. After a string is plucked, it will move from right to left. On one side, it will compress the air particles. However, as it returns to the other side, pressure decreases, and rarefaction occurs. Sound waves are no longer produced once the string stops oscillating and becomes stationary.
Where do sound waves travel?
Sound waves require a medium to be produced. Without the presence of these molecules, a vacuum is formed, and sound cannot be created. For example, in a guitar, the air molecules inside the sound hole and around the strings vibrate, acting as the medium and carrying the sound waves to produce music.
In an ultrasound scan, sound waves travel through the skin to reach the tissue boundaries. A gel is applied to the skin to prevent air pockets from forming between the transducer and skin as ultrasound waves have a harder time travelling through air. By removing the air pockets, a clearer image is obtained.
Do take note that the speed of sound will differ depending on the medium it travels through. Sound travels fastest in solids and slowest in gases. The more closely packed the particles are, the faster the vibrations travel through the molecules.
How are echoes produced?
In music, the terms ‘echo’ and ‘reverb’ are often used interchangeably. However, they refer to different things. An echo is the single reflection of sound after a delay. Conversely, a reverb consists of multiple echoes so close together they appear to be continuous.
Echoes are produced when the original sound gets reflected after it bounces off a surface. The delay is directly proportional to the distance between the listener and the reflecting surface; the closer the listener is to the surface, the faster they hear the echo.
We rarely pay attention to sound, but we also cannot live without it. These examples mentioned above are just a tiny glimpse of how sound, and by extension physics, affect our daily lives. There are numerous applications still to be discovered, and you can have fun exploring them.
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