36. Sound
How does sound travel?
Huge impacts and explosions take place in space all the time. Why do we not hear them? The reason is that the production and movement of light requires a substance that can vibrate.
In space, these substances are few and far between. As a result, no vibrations or sound waves can be formed.
On Earth, the situation is different. Here, the air can act as a medium through which the vibration can reach the listener's ears.
Sound travels well through the atmosphere. However, it moves even better through water and iron. In empty space, it cannot move at all.
Sound waves
A sound is formed when the air is made to vibrate. As a result, sound waves are produced. They can be produced in various ways. A small, long leaf can be used to produce a simple sound. When it is held tightly between the thumbs of your hands and movement is blown to it, the result is a sound.
The leaf of a reed is perfect for producing such a sound. However, a similar sound can be achieved even with blades of grass or a small piece of paper.
Blowing on an edge
Another way of producing sound is by blowing on an edge.An edge makes the air vibrate, because every other air molecule must turn in one direction and every other molecule in the opposite direction. The whistling sound of wind is usually produced in such a way.
The sound of a whistle is created when air flow is made to travel through the whistle and touch its sharp edge.
Vocal cords
The third way of producing sounds is by using the vocal cords (also known as vocal folds).
The vocal cords are a structure found in the human larynx.
When air is made to travel through the larynx during exhalation, the vocal cords begin to vibrate. This causes the air itself to vibrate, as well. As a result, a sound is formed.
Strings and film
The fourth way to produce sound is to make a string or a film vibrate. The string or a film is struck, hit or rubbed. As a result, the string or the film begins to vibrate, making the air around it vibrate, as well.
Many musical instruments, such as the guitar and the drums, produce sound in this way. The strings of the guitar vibrate, as do the drumheads of various drums.
Volume
The more air is made to move and vibrate, the stronger the volume of the sound becomes. This is why many instruments, such as the violin, have hollow bodies. The hollow body amplifies the sound that is produced with the instrument's strings.Pianos also have hollow, wooden bodies. Without this body, the only sound would be produced with strings. The result would be a very quiet, thin sound.
The hollow body makes a large amount of air vibrate inside it. This causes sound waves to travel to the listener's ears.
Tubes and horns are also useful in amplifying sounds.
Pitch
The less mass a string contains, the faster it will vibrate. The result of such a fast vibration is a high-pitched sound. This can be seen in many instruments. For example, the larger note blocks of a xylophone produce lower sounds, whereas smaller blocks produce higher sounds.
Similarly, the shorter a tube is, the faster the vibration inside it is. The result is a high-pitched sound. The function of the pan flute is based on this phenomenon.
The length of a tube can be adjusted with water (such as in water flutes) or by opening holes inside the tube (the recorder and the flute). If a tube consists of two parts, it can be made shorter by pressing one half of the tube inside the other half (such as in the slide trombone).
The shorter and thinner a string is, the higher the sound it produces is. The strings on the left-hand side of the piano are longer, which means that they produce lower sounds than the shorter strings on the right-hand side.
The pitch of a sound can also be adjusted by tightening the string. This is done with many stringed instruments, such as the guitar or the violin.
Terminology
| Term | Explanation |
|---|---|
| sound wave | A phenomenon where air vibrates at a certain frequency. |
| hollow body | The resonating, hollow part of a stringed instrument that amplifies the instrument's sound. |