Propagation of Sound

Discover how sound travels through different media, understand sound waves as mechanical waves, and learn about their characteristics and speed!

Sound in Medium
Medium: Air
Sound needs a medium to travel. Particles vibrate about their mean position but don't travel forward.

Mechanical Wave
Compressions & Rarefactions
C - R - C - R
Sound travels as alternating compressions (high pressure) and rarefactions (low pressure).

Longitudinal Wave
Sound Propagates as Density & Pressure Variations
Density Variation
Pressure Variation
Sound waves carry energy through alternating regions of high and low density/pressure
Pitch & Frequency
Low frequency = Low pitch
Loudness & Amplitude
Small amplitude = Soft sound
Wave Speed Formula
v = λ × ν
Where:
v = speed of sound (m/s)
λ = wavelength (m)
ν = frequency (Hz)

Also: ν = 1/T
T = time period (s)
Sound Wave Calculator
Enter values to calculate speed
Select a wave characteristic
Use the buttons below to explore different characteristics of sound waves
Wave Type: Longitudinal
Particle Motion: Parallel to wave
Example: Sound waves
Region: Compression
Pressure: High
Density: Maximum
Region: Rarefaction
Pressure: Low
Density: Minimum
Wavelength (λ): 35 cm
Frequency (ν): 440 Hz
Amplitude: Medium
Sound in Solids
Speed: ~5960 m/s (steel)
Particles closely packed
Fastest transmission
Sound in Liquids
Speed: ~1498 m/s (water)
Moderate particle density
Medium transmission
Sound in Air
Speed: ~344 m/s (22°C)
Particles far apart
Slowest transmission
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 Sea Water 1531
Distilled Water 1498
Ethanol 1207
Methanol 1103
Gases Hydrogen 1284
Helium 965
Air 346
Oxygen 316
Sulphur dioxide 213

Activity 11.4: Slinky Wave Demonstration

Step 1: Setup
Take a slinky. You and your friend hold opposite ends and stretch it.
Example 11.1
Problem: A sound wave has a frequency of 2 kHz and wavelength 35 cm. How long will it take to travel 1.5 km?
Given:
Frequency, ν = 2 kHz = 2000 Hz
Wavelength, λ = 35 cm = 0.35 m
Distance, d = 1.5 km = 1500 m
Find Speed:
v = λ × ν
v = 0.35 × 2000 = 700 m/s
Calculate Time:
t = d / v
t = 1500 / 700 = 2.14 s
Time taken = 2.14 seconds

Practice Questions

Q1.
What are sound waves? Why are they called mechanical waves?
Answer:
Sound waves are disturbances that travel through a medium when particles of the medium set neighboring particles into motion. They are called mechanical waves because:
• They require a material medium for propagation
• They involve the motion of particles in the medium
• The particles vibrate about their mean position but don't travel forward
Q2.
Distinguish between compressions and rarefactions.
Answer:
Compressions:
• Regions of high pressure
• Particles are crowded together
• Maximum density of particles

Rarefactions:
• Regions of low pressure
• Particles are spread apart
• Minimum density of particles
Q3.
Calculate the wavelength of a sound wave whose frequency is 220 Hz and speed is 440 m/s in a given medium.
Solution:
Given: Frequency (ν) = 220 Hz
Speed (v) = 440 m/s

Using: v = λ × ν
λ = v / ν
λ = 440 / 220 = 2 m

Answer: Wavelength = 2 m
Explore Sound Propagation
Understanding Sound Propagation
Sound is produced by vibrating objects and travels through a medium (solid, liquid, or gas). The disturbance moves through the medium, not the particles themselves. Particles only vibrate about their mean position, making sound a mechanical wave.
v = λ × ν
Speed of Sound = Wavelength × Frequency
SI Units: Speed (m/s), Wavelength (m), Frequency (Hz)
Nature: Longitudinal mechanical wave
Sound Wave Characteristics
• Frequency: Number of oscillations per second (Hz)
• Wavelength: Distance between consecutive compressions
• Amplitude: Maximum displacement from mean
• Time Period: Time for one complete oscillation
• Pitch: How brain interprets frequency
• Loudness: Determined by amplitude
Longitudinal Waves
• Particles oscillate parallel to wave direction
• Create compressions and rarefactions
• Compression: High pressure region
• Rarefaction: Low pressure region
• Sound cannot travel in vacuum
• Speed depends on medium properties
Key Points to Remember
• Sound needs a medium to travel - it cannot travel through vacuum
• Speed of sound: Solids > Liquids > Gases
• Speed increases with temperature
• Sound travels slower than light (that's why we see lightning before hearing thunder)
• Frequency remains constant when sound travels through different media
• Higher frequency = Higher pitch; Greater amplitude = Louder sound
• Sound intensity decreases with distance from source