Sound Energy

Sound energy is a form of kinetic energy caused by the physical vibration of

air particles or molecules. The particles collide with other neighboring
particles causing them to vibrate. These vibrations travel in a straight line.
When they reach our ears, we perceive them as sound.

A sound is a vibration that propagates through a medium in the form of

a mechanical wave. The medium in which it propagates can either be a solid, a
liquid or a gas. Sound travels fastest in solids, relatively slower in liquids and
slowest in gases.

In physics, the sound is defined as

A vibration that propagates as an audible wave of pressure, through a medium

such as a gas, liquid or solid

Examples

Sound energy is derived from an external source. Here are some examples of
how sound is generated.

 Car honking
 Airplane taking off
 Police whistling
 Dog barking
 Wind howling
 Baby crying
How does Sound Energy Work

The particles vibrate about their position until they reach an equilibrium. The
vibrations, and hence sound, are transmitted in the form of a wave, known as a
sound wave. The particles vibrate in the same direction as the wave propagates.
Such type of wave is known as a longitudinal wave. The sound wave carries energy
and keeps traveling until it loses energy.

Sound requires a medium to propagate. It can travel through air, water, wood,
glass, or metal. Unlike light, sound cannot propagate in a vacuum since there are
no particles to transmit the wave.
How does Sound Wave Transfer Energy to Your Ears

When sound waves reach our ears, they are funneled to the eardrum. The
eardrum is a part of the ear that converts sound energy into mechanical
movements. It vibrates when struck, and a fluid carries the vibrations through
three connected bones. The moving fluid bends a series of hair-like cells that
convert the vibrations into nerve impulses. These impulses are carried to the
brain by auditory nerves. The brain interprets them as sound.

What is a Soundwave?

A sound wave is the pattern of disturbance caused by the energy travelling away
from the source of the sound. Sound waves are longitudinal waves. This means
that the propagation of vibration of particles is parallel to the energy wave
propagation direction. When the atoms are set in vibration they move back and
forth. This continuous back and forth motion results in a high-pressure and a
low-pressure region in the medium. These high- pressure and low-pressure
regions are termed compressions and rarefactions, respectively. These regions
are transported to the surrounding medium resulting in the sound waves
travelling from one medium to another.

Nature of Sound

The sound produced by a guitar is different from the sound produced by a drum.
This is because the sound produced by different sources have different
characteristics. Sound can be characterized by its frequency, wavelength, and
amplitude.

 Frequency of sound

The number of rarefactions and compressions that occur per unit time is known
as the frequency of a sound wave. The formula of the frequency of a wave is given
as:
 𝟏
f=
𝑻

Where,

 f is the frequency of a sound wave and

 T is the time period.

 Wavelength of sound

The distance between the successive compression and rarefaction is known as

the wavelength of a sound wave. The wavelength of the sound formula is given
as follows:

𝒗
λ=
𝒇

Where, f is the frequency of the sound wave and v is the velocity of the sound
wave.

Amplitude of sound

The amplitude of the sound is the magnitude of the maximum disturbance in a

sound wave. The amplitude is also a measure of energy. Higher the amplitude
higher the energy in a sound wave. Humans can hear a limited range of
frequencies of sound. Physicists have identified the audio frequency spectrum of
the human ear to be between 20 Hz and 20,000 Hz. Under ideal laboratory
conditions, the human ear can detect frequencies that are as low as 12 Hz and
as high as 20,000 Hz.

Speed of Sound

The speed at which sound waves propagate through a medium is known as the
speed of sound. The speed of sound is different in different media. The speed of
sound is highest in solids because the atoms in solid are highly compressed. The
interaction between atoms in a particle is highly dependent on the distance
between them. Higher the interaction between the atoms, the quicker the energy
is transferred. As the interaction of the particles in solids is high, the speed of
sound is faster than liquids and gases. The table below lists the speed of sound
in different media. The formula used to calculate the speed of sound is given as:

𝒅
c=
𝒕

Where,

 d is the distance traveled by sound

 t is the time taken to cover the distance.
Medium Speed of sound

Water 1481 m/s

Air 343.2 m/s

Copper 4600 m/s

Hydrogen 1270 m/s

Glass 4540 m/s

How is Sound Energy Measured

The intensity of sound is measured in the unit of decibels or dB, named after
Scottish-born inventor Alexander Graham Bell. Bell invented the audiometer, a
device that measures how well a person can hear sound. The decibel scale is
logarithmic, which means that it represents the ratio of two measurable physical
quantities. Similarly, sound pressure can also be expressed in dB. For example,
a normal speaking voice is 60 dB. The sound of an airplane taking off is 115 dB.

Sound wave frequency is measured in the unit of Hertz or Hz. One Hertz is equal
to one sound vibration in one second. For a human to hear the sound, the
frequency must be between 20 and 20,000 Hz. Any frequency below 20 Hz is
 called infrasound; above 20,000 Hz is called ultrasound. These two types of
sound are inaudible to the human ear.

Reflection of Sound

Reflection of sound is similar to the reflection of light. The reflection of sound

obeys the following laws of reflection

 The angle of incidence is equal to the angle of reflection.

 The incident sound, the normal sound and the normal sound all lie in
the same plane.
When a sound hits a hard surface, it reflects back to its source. This reflection of
sound is otherwise is called an echo. Hard surfaces have a tendency to reflect
sound while soft surfaces absorb sound and silence them. If the frequency of the
sound wave is low, then the sound wave will not get reflected. Sometimes, we
hear multiple echoes from a source of sound if the area is large and has multiple
reflecting surfaces such as valleys and huge empty rooms. This phenomenon is
known as reverberation.

Conversion of Sound Energy

From the energy conservation law, energy can neither be created nor destroyed.
It can be transferred from one form to another. Here are some examples of how
sound energy can be converted into other forms and vice versa.

 A microphone converts sound energy to electrical energy

 A loudspeaker converts electrical energy into sound energy
 A drummer converts mechanical energy into sound energy
 An electric bell converts electrical energy into sound energy

Uses

The primary use of sound energy is for hearing. Aside, it has other applications.

 Scientists use infrasonic sound to predict an earthquake, volcano, and avalanche

 A particular type of sound, SONAR (Sound Navigation And Ranging), is used to
map the ocean floor
 Doctors use ultrasound to cure tumor cells of a cancer patient without any
physical pain
 Doctors also use ultrasound on pregnant women to detect any abnormality in the
fetus
 Ultrasound is used in the industry to detect any flaws in machinery parts and to
determine the thickness of metal
 Soothing musical sound from Tibetian bowls can remove stress and body pain
 Bats produce ultrasonic waves to communicate among themselves and to find
obstacles in their path

Why are sound waves called mechanical waves?

In which medium does the sound wave travel the fastest?

What is the frequency of a sound wave?

In which medium is the speed of sound the lowest?

What is the reverberation of sound?