This article explains how sound travels at different speeds through solids, liquids, and gases, the factors affecting it, and related phenomena like sonic booms and SONAR, in a simple and student-friendly way.
What Is Sound and How Does It Travel?
Sound is a mechanical wave produced by vibrating objects. These vibrations create disturbances in the surrounding medium, which propagate in the form of compressions and rarefactions.
- Compressions: Regions where particles are close together (high pressure).
- Rarefactions: Regions where particles are far apart (low pressure).
This alternate compression and rarefaction pattern travels through the medium as a longitudinal wave.
Important:
- It is the energy of the sound that travels through the medium, not the particles themselves.
- Sound cannot travel in a vacuum because there are no particles to transmit vibrations.
Speed of Sound
The speed of sound is the distance travelled by a sound wave per unit time through a medium.
Mathematically,
The speed of sound depends on how quickly particles of the medium can transfer vibrations to one another. It varies greatly between solids, liquids, and gases.
Factors Affecting the Speed of Sound
A. Nature of the Medium
Sound travels at different speeds in different materials because of variations in density, elasticity, and temperature.
1. Solids: Sound travels fastest in solids because particles are closely packed, allowing vibrations to transfer quickly.
2. Liquids: Sound travels slower than in solids but faster than in gases.
3. Gases: Sound travels slowest in gases since particles are far apart.
B. Temperature
As the temperature of a medium increases, its particles move faster, transferring sound energy more efficiently.
Hence, speed of sound increases with temperature.
Example:
- In air at 0°C, the speed of sound is 331 m/s.
- At 22°C, it increases to 344 m/s.
C. Elasticity and Density
- Elasticity: The more elastic the medium (the ability to regain shape), the faster sound travels.
- Density: Denser materials with less elasticity slow down sound.
Speed of Sound in Different Media
The speed of sound varies based on the type of material and its temperature.
Table: Speed of Sound in Different Media at 25°C
| State | Substance | Speed (m/s) |
|---|---|---|
| Solids | Aluminium | 6420 |
| Nickel | 6040 | |
| Steel | 5960 | |
| Iron | 5950 | |
| Brass | 4700 | |
| Glass (Flint) | 3980 | |
| Liquids | Water (Sea) | 1531 |
| Water (Distilled) | 1498 | |
| Ethanol | 1207 | |
| Methanol | 1103 | |
| Gases | Hydrogen | 1284 |
| Helium | 965 | |
| Air | 346 | |
| Oxygen | 316 | |
| Sulphur dioxide | 213 |
Observations:
- Sound travels fastest in solids and slowest in gases.
- Among gases, hydrogen has the highest speed of sound because it is light and has low density.
- In liquids, seawater conducts sound faster than pure water due to dissolved salts.
Speed, Wavelength, and Frequency Relationship
The speed of sound (v), wavelength (λ), and frequency (f) are related by:
- Wavelength (λ): Distance between two consecutive compressions or rarefactions.
- Frequency (f): Number of vibrations per second (measured in Hertz).
Note:
The speed of sound remains almost constant for all frequencies in a given medium under the same physical conditions.
The Sonic Boom
When an object moves faster than the speed of sound in air (about 343 m/s at room temperature), it is said to be moving at supersonic speed.
Examples: Jet aircrafts, bullets, and rockets.
What Happens:
- A shock wave is produced as the object breaks the sound barrier.
- The pressure variations from these waves create a loud explosive sound, known as a sonic boom.
Key Points:
- Shock waves carry a large amount of energy.
- Sonic booms can shatter glass and damage nearby structures due to high air pressure changes.
SONAR – Sound Navigation and Ranging
SONAR stands for SOund Navigation And Ranging. It is a device that uses ultrasonic waves (sound waves above 20 kHz) to detect underwater objects.
Working Principle:
- A transmitter sends ultrasonic waves into water.
- These waves strike underwater objects (like the seabed or a submarine) and get reflected back.
- A detector receives the reflected waves and converts them into electrical signals.
- The time taken for the echo to return helps calculate distance, direction, and speed of objects underwater.
Formula:
Applications:
- Measuring ocean depth.
- Locating submarines and shipwrecks.
- Fish finding and underwater communication.
Intensity, Loudness, and Pitch of Sound
A. Intensity of Sound
The intensity of sound is the amount of sound energy passing through a unit area per second.
It determines the strength of a sound wave.
B. Loudness
Loudness is how our ears perceive the strength of sound. It depends on the amplitude of vibration:
- Larger amplitude → Louder sound
- Smaller amplitude → Feeble sound
Even if two sounds have the same intensity, one may seem louder due to the sensitivity of our ears.
C. Pitch or Shrillness
Pitch depends on the frequency of vibration:
- Higher frequency → Shriller or higher-pitched sound (e.g., a whistle).
- Lower frequency → Deeper or lower-pitched sound (e.g., a drum).
Audible and Inaudible Sound Ranges
The human ear can detect sounds within a specific frequency range known as the audible range.
| Type of Sound | Frequency Range | Example |
|---|---|---|
| Infrasonic | Below 20 Hz | Earthquakes, elephant calls |
| Audible | 20 Hz – 20,000 Hz | Human speech, music |
| Ultrasonic | Above 20,000 Hz | SONAR, medical imaging |
More to Know – Interesting Facts
- Sound travels faster in warm air than in cold air.
- Speed of sound in air at 0°C = 331 m/s, and at 20°C = 343 m/s.
- Sound cannot travel through space because there is no medium.
- The time gap between an echo and original sound must be at least 0.1 seconds for the human ear to distinguish them.
- Elastic and inertial properties of the medium jointly determine sound speed — higher elasticity and lower inertia lead to faster sound propagation.
Speed of Sound in Media
| Medium | Speed (m/s) |
|---|---|
| Air (0°C) | 331 |
| Air (20°C) | 343 |
| Helium | 965 |
| Hydrogen | 1284 |
| Water (0°C) | 1402 |
| Water (20°C) | 1482 |
| Seawater | 1522 |
| Aluminium | 6420 |
| Copper | 3560 |
| Steel | 5941 |
| Granite | 6000 |
| Rubber | 54 |
Summary
| Concept | Key Point |
|---|---|
| Nature of Sound | Longitudinal mechanical wave |
| Medium Required | Cannot travel in vacuum |
| Speed Dependence | Depends on medium, temperature, elasticity, and density |
| Fastest Medium | Solids |
| Slowest Medium | Gases |
| Formula | Speed = Wavelength × Frequency |
| SONAR | Uses ultrasonic waves to locate underwater objects |
| Sonic Boom | Caused when an object moves faster than sound |
FAQ
Q1. Why does sound travel faster in solids than in gases?
Because particles in solids are tightly packed and can transfer vibrations faster.
Q2. What is the speed of sound in air at room temperature?
Approximately 343 m/s at 20°C.
Q3. Why can’t sound travel in space?
Space is a vacuum, so there are no particles to transmit sound waves.
Q4. What causes a sonic boom?
A sonic boom occurs when an object moves faster than the speed of sound, producing shock waves in air.
Q5. What is the working principle of SONAR?
SONAR works on the reflection of ultrasonic waves to detect the distance and movement of underwater objects.
