Production and Propagation of Sound

Have you ever wonder how are we able to hear different sounds produced around us. How are these sounds produced? Or how a single instrument can produce a wide variety of sounds? Also, why do astronauts communicate in sign languages in outer space? A sound is a form of energy that helps in hearing to living beings. It is a form of kinetic mechanical energy which moves in a form of a wave.  The sound waves show vibrational motion. Hertz (Hz) and  Decibel (dB) are widely used measurement units to measure sound.

Types of Sound

• There are different types of sound like audible, inaudible, pleasant, and unpleasant.
• The waves which frequency ranges below 16Hz are called infrasonic waves. These waves are used for the detection of an earthquake, volcanic eruption, petrol formations underground, etc.
• Whereas, the waves which frequency ranges above 20kHz are called ultrasonic waves. These waves are used by some animals to locate their prey and communicate like bats, etc.
• The waves having a frequency between 16Hz to 20kHz are audible to humans.

Production of Sound

Sound is produced by the rapid to and fro movement of an object i.e. vibration. The object set to vibration disturbs the equilibrium state of the particles in the medium and vibration keeps transmitting from one particle to another. 

The vibration of the body is the primary source of sound’s genesis. The emission of sound continues as long as a body’s vibration remains. By traveling across a continuous elastic membrane, this sound generates a hearing experience in our ears. 

As an example: When a tuning fork is struck, it vibrates and emits sound. The vibration will stop if the tuning fork is touched with your hand. As a result, sound output will be reduced. In the picture, as a tuning fork emits sounds, a pinball in contact with one of the tuning fork’s arms continually travels away from the arm owing to the fork’s vibration. 

We can comprehend the origin and character of sound based on our everyday experiences. For example, if a metal object falls to the floor or is struck by a hammer, a sound is generated; but, if it is grasped by hand or a hard object. Sound is created by blowing on a flute, plucking a musical instrument’s string, or vibrating the membrane of a drum. As a result, it is clear that sound is created by vibration. This vibration generates waves in the medium, which oscillates the membrane of our ears, allowing us to perceive sound.

The vibration of a body causes the sound to be generated. The vibration of the body is the primary generator of all types of sound. Mechanical energy is converted into sound as a result of vibration.

Propagation of Sound

Sound is produced by the rapid to and fro movement of an object i.e. vibration. The object set to vibration disturbs the equilibrium state of the particles in the medium and vibration keeps transmitting from one particle to another. e.g. when a tuning fork is struck against a rubber pad vibration created in the prongs can be noticed and brought near our ears we can sense the sound being produced, guitar strings produce sound when struck, etc.

The traveling of sound from the sound source to the surrounding medium is the propagation of sound. Sound waves cannot travel in a vacuum as there are no molecules present to set vibration.

Speed of Sound in Different Mediums 

 The average speed of sound is 343m/s. Sound travels in the form of waves from one medium to another. Speed of sound varies in different mediums. It is affected by factors like temperature, density, elasticity of the medium through which sound waves travel. We have listed the speed of sound in different mediums in the table below:

Materials	Speed of sound
Air at 20° C	343 m/s
Rubber	60 m/s
Lead	1210 m/s
Gold	3240 m/s
Glass	4540 m/s

Can Sound Travel in a Vacuum or Space?

Sound always requires a medium to travel from one point to another. Sound cannot propagate in a vacuum because there are no particles or molecules present to set vibration. The music produced by the vibration of guitar strings can be heard as the vibration produced travels through the air to our ears. In this process air acts as a medium of transmission of sound.

How is the Sound Heard by Humans? 

Sound waves traveling through a medium reach our ears, and we hear the sound. As the sound waves are gathered by the pinna of our ear and then lead to the ear canal where they strike the eardrum. The vibration set from the eardrum is transmitted to three bones (hammer, anvil, stirrup) and finally to the inner ear. The sensitive cells present in the inner ear transmit the vibration to the brain through the auditory nerve which is registered as sound by the brain.

Read More,

• Characteristics of Sound Waves
• Sound Waves are Longitudinal Waves

Sample Problems

Problem 1: Why sound can’t be heard in space? Give reason.

Solution: 

Sound travels in the form of wave which is created due to the vibration of particles in medium as air, water or solid materials. Because space do not have any particles to vibrate due to the lack of medium sound cannot travel or be heard in space.

Problem 2: All vibrating bodies produce sound. Are we able to hear all the sounds?

Solutions:

The sound waves which frequency ranges below 16Hz are called infrasonic sound and the waves which frequency ranges above 20kHz are called ultrasonic sound. And, the general range of human hearing is 20Hz to 20kHz. Hence, the sound waves ranging out this limitation cannot be heard by humans.

Problem 3: Do all bodies produce sound?

Solution: 

Sound is produced due to the vibration of particles of the medium. Hence, if a body is kept in contact with a medium the particles can vibrate and produce sound but, if the body is kept in vacuum sound will not be produce as the vibration of particles will not take place.

Problem 4: Name the factor that determines the shrillness of a sound?

Solution: 

The frequency of waves determines the shrillness of sound. As the sound wave with higher frequency creates high pitch and with lower frequency the pitch gets low.

Problem 5: The sound from a mosquito is produced when it vibrates its wings at an average rate of 250 vibrations per second, what is the time period of the vibrations?

Solution:

Given that, 

The total vibrations are 250 Hz.

Therefore,

Time is taken to complete one vibration =1/250=0.004 seconds.

Hence, the time period = 0.004 seconds.