Light and Sound
Concept : Sources and Properties of Sound
What is sound?
A sound is a form of energy that travels in waves through solid, liquid and gaseous media. The phenomenon of sound waves travelling through any medium is almost similar to the ripples on a water surface after a small rock is tossed in a waterbody.
How is sound produced?
- Sounds are created when an object vibrates, and as a result, the air surrounding the object also starts to vibrate. This is how sound reaches our ear through the waves of vibrations.
- Vibrations are usually caused by the rapid back and forth movement of the object’s molecules. Similarly, the air molecules surrounding the object also show such rapid movements.
Sources of sound:
Sources of sound can be divided into two types—
1. Natural sources of sound:
These sources can produce sound naturally.
Rustling of leaves
2. Man-made/Artificial sources of sound:
These are sources of sounds that man artificially makes.
Pleasant and unpleasant sounds:
Sounds that make us feel happy and are pleasing to our ears are called pleasant sounds, whereas sounds that are uncomfortable to hear, cause irritation and may lead to temporary hearing impairment when heard continuously for a long time are called unpleasant sounds.
|Pleasant sounds||Unpleasant sounds|
|Sounds of a flute||Sounds of a hammer|
|Sounds of a piano||Car horns and truck horns|
|Sounds of a violin||Electrical generator sounds|
|Sounds of a guitar||Gunshot sounds|
How do humans produce sounds?
- There are specific components in our body that help us make sounds.
- The larynx, also called the speech box, generates sound.
- The larynx is situated at the top of the windpipe in our throat.
- There are two ligaments in the larynx, called the vocal cords.
- Stretching of vocal cords allows us to make sounds.
- The vocal cords are connected to muscles that change the stretching of the cords. The muscles also change the space between the cords.
- Air is passed between the two vocal cords with the help of the lungs.
- As a result, the vocal cords start vibrating, thereby producing sound.
- The sounds are made by the vibration of the vocal cords caused by the expelled air.
- When the vocal cords are stretched, we make high sounds, and when the cords are relaxed, we make low sounds. This is known as the pitch of the sound.
Amplitude and pitch:
- Amplitude measures the loudness or quietness of a sound.
- Pitch denotes how high or how low a sound is.
- A high pitch sound has more vibrations, but a low pitch sound has fewer vibrations.
Interactions of sound with objects:
Sound waves can interact with objects in the following ways—
- When sound waves strike a surface and then bounce off, it is called a reflection of sound.
Examples: A very common example of the reflection of sound is the occurrence of echo. It is nothing but the repetition of sound caused due to the reflection of the sound waves.
- When sound waves get absorbed, instead of getting reflected by a sound-absorbing material, it is called absorption of sound.
Examples: Sound absorbing materials are installed in cinema halls, auditoriums, etc. so that the loud noise created in that space is not heard from outside.
Hearing impairment: The inability of a person to hear sounds properly.
Ligament: It is a band of tissue that holds bones and organs in their proper locations.
Did You Know?
- The sound of an approaching train can be heard if we put our ears to the railway tracks that are made of steel. It happens because sound travels faster in a solid medium than in a gaseous medium.
- Unlike light, sound cannot travel through a vaccuum. It needs a medium (solid, liquid or gas) to travel.
- Animals with large ears can hear better than animals with small ears.