Speed of Sound in Different Media

Introduction

Sound travels through a material medium in the form of waves. The speed at which sound travels is called the speed of sound.

The speed of sound is not the same in all media. It depends on the nature of the medium through which sound is travelling.

Sound travels fastest in solids, slower in liquids, and slowest in gases.

Speed of Sound Depends on Medium

Sound travels by the vibration of particles of a medium. Therefore, the arrangement of particles in the medium affects the speed of sound.

In solids, particles are very closely packed. In liquids, particles are less closely packed than solids. In gases, particles are far apart.

Because of this difference, sound travels with different speeds in solids, liquids, and gases.

Order of Speed of Sound

The speed of sound in different media generally follows this order:

Solids > Liquids > Gases

This means sound travels fastest in solids, slower in liquids, and slowest in gases.

Sound in Solids

Sound travels fastest in solids because the particles of solids are very close to each other.

When one particle vibrates, it quickly transfers the disturbance to the neighbouring particles. Due to this quick transfer of vibrations, sound travels faster in solids.

Examples

Sound travels quickly through steel.
Sound can travel through railway tracks.
Sound can travel through wooden doors and walls.
Sound can travel through metal pipes.

Sound in Liquids

Sound also travels through liquids. In liquids, particles are not as closely packed as in solids, but they are closer than particles in gases.

Therefore, sound travels slower in liquids than in solids but faster than in gases.

Examples

Sound can travel through water.
Aquatic animals can communicate using sound waves.
Divers can hear sounds underwater.
SONAR uses sound waves in water to detect underwater objects.

Sound in Gases

Sound travels slowest in gases because the particles of gases are far apart.

Since the particles are far from each other, the transfer of disturbance from one particle to another takes more time.

Air is a gas, and most sounds that we hear in daily life reach us through air.

Examples

We hear a teacher’s voice through air.
We hear music from a speaker through air.
We hear thunder through air.
We hear a bell ringing because sound travels through air.

Figure

Explanation of the Figure

The figure compares the arrangement of particles in solids, liquids, and gases.

In solids, particles are very close, so sound vibrations are transferred quickly. Therefore, sound travels fastest in solids.

In liquids, particles are less close, so sound travels slower than in solids. In gases, particles are far apart, so sound travels slowest.

Approximate Speed of Sound in Different Media

The speed of sound has different values in different media. Some approximate values are given below:

Medium	Approximate Speed of Sound	Type of Medium
Air	\(340\,m\,s^{-1}\)	Gas
Water	\(1500\,m\,s^{-1}\)	Liquid
Steel	\(5000\,m\,s^{-1}\)	Solid

Comparison of Air, Water and Steel

Sound travels much faster in water than in air. It travels even faster in steel than in water.

Sound travels about 4 to 5 times faster in water than in air.
Sound usually travels about 15 to 20 times faster in solids than in air.
Sound travels fastest in steel among air, water, and steel.

Steel > Water > Air

Why Sound Reaches Faster Through Steel Than Air

If a person knocks one end of a long steel fence, the sound can reach the other end through both steel and air.

The sound travelling through steel reaches earlier because sound travels much faster in steel than in air.

This happens because steel particles are closely packed and transfer vibrations more quickly than air particles.

Speed of Sound in Air

The speed of sound in air is not fixed for all conditions. It changes with temperature and humidity.

In dry air:

At \(0^\circ C\), the speed of sound is about \(331\,m\,s^{-1}\).
At \(22^\circ C\), the speed of sound is nearly \(344\,m\,s^{-1}\).

Thus, the speed of sound in air increases when temperature increases.

Higher temperature → Higher speed of sound in air

Effect of Humidity on Speed of Sound

Humidity also affects the speed of sound in air.

When humidity increases, the speed of sound in air also increases.

Higher humidity → Higher speed of sound in air

Speed Depends on Medium, Not on Source

In most media, such as air, the speed of sound depends mainly on the medium and its conditions.

It does not depend on the source of sound or on the frequency of the sound source.

If frequency changes in the same medium, the wavelength changes, but the speed remains almost constant under the same conditions.

Same medium + same conditions → Speed remains almost constant

Relation Between Speed, Frequency and Wavelength

The speed of sound is related to wavelength and frequency by the formula:

\(v=\lambda\nu\)

where,

\(v\) = Speed of sound
\(\lambda\) = Wavelength
\(\nu\) = Frequency

If the speed remains constant in a medium, then higher frequency means shorter wavelength, and lower frequency means longer wavelength.

Example 1

A sound wave travels in air with speed \(340\,m\,s^{-1}\). If its frequency is \(170\,Hz\), find its wavelength.

Given,

Speed, \(v = 340\,m\,s^{-1}\)
Frequency, \(\nu = 170\,Hz\)

Using,

\(v=\lambda\nu\)

Therefore,

\(\lambda=\frac{v}{\nu}\)

\(\lambda=\frac{340}{170}\)

\(\lambda=2\,m\)

Therefore, the wavelength of the sound wave is \(2\,m\).

Example 2

A sound wave travels \(1500\,m\) in water in \(1\,s\). Find the speed of sound in water.

Given,

Distance = \(1500\,m\)
Time = \(1\,s\)

Using,

\(v=\frac{\text{distance}}{\text{time}}\)

\(v=\frac{1500}{1}\)

\(v=1500\,m\,s^{-1}\)

Therefore, the speed of sound in water is \(1500\,m\,s^{-1}\).

Examples from Daily Life

Sound reaches faster through railway tracks than through air.
A knock on a metal pipe can be heard quickly at the other end.
Sound travels through water, so underwater communication is possible.
We hear most sounds in daily life through air.
Thunder is heard after lightning because sound travels much slower than light.
In warm air, sound travels slightly faster than in cold air.

Important Terms

1. Speed of Sound

The distance travelled by a sound wave in unit time is called the speed of sound.

2. Medium

The material through which sound propagates is called a medium.

3. Solid Medium

A medium in which particles are closely packed, such as steel or wood.

4. Liquid Medium

A medium in which particles are less closely packed than solids, such as water.

5. Gaseous Medium

A medium in which particles are far apart, such as air.

6. Wavelength

The distance between two consecutive crests or troughs of a wave.

7. Frequency

The number of complete oscillations per unit time.

Important Points

The speed of sound depends on the medium through which it travels.
Sound travels fastest in solids.
Sound travels slower in liquids than in solids.
Sound travels slowest in gases.
The general order of speed of sound is: solids > liquids > gases.
Sound travels about \(340\,m\,s^{-1}\) in air.
Sound travels about \(1500\,m\,s^{-1}\) in water.
Sound travels about \(5000\,m\,s^{-1}\) in steel.
The speed of sound in air increases with temperature.
The speed of sound in air also increases with humidity.
In the same medium under the same conditions, speed remains almost constant.
The relation between speed, wavelength and frequency is \(v=\lambda\nu\).

Conclusion

The speed of sound depends on the medium through which sound travels. Sound travels fastest in solids because their particles are very closely packed. It travels slower in liquids and slowest in gases because the particles are less closely arranged. In air, the speed of sound also depends on temperature and humidity. The general order of speed of sound is solids > liquids > gases. The relation between speed, wavelength, and frequency is \(v=\lambda\nu\).