Sound waves are vibrations that travel through matter, carrying energy from one place to another. This section explores their key properties, including frequency, wavelength, and amplitude. We'll see how these characteristics affect our perception of sound and how waves behave in different media.

Understanding sound waves is crucial for grasping how we hear and interact with our environment. We'll look at how pitch relates to frequency, loudness to amplitude, and examine the differences between longitudinal and transverse waves. This knowledge forms the foundation for studying more complex acoustic phenomena.

Sound wave characteristics

Fundamental properties of sound waves

• Sound waves propagate through a medium by vibrating particles
• Mechanical waves require a medium for transmission
• Frequency measures complete oscillations per unit time in Hertz (Hz)
• Wavelength represents distance between consecutive compression points
• Amplitude indicates maximum particle displacement from equilibrium
• Wave equation relates speed, frequency, and wavelength: $v = f\lambda$
• Sinusoidal waves graphically represent pressure variations over distance/time
• Wave energy proportional to square of amplitude

Sound wave behavior in different media

• Speed of sound depends on propagation medium
• Fluids (gases and liquids) transmit only longitudinal sound waves
• Solids can propagate both longitudinal and transverse sound waves
• Longitudinal waves travel faster than transverse waves in same medium
• Acoustic impedance affects sound transmission between media
• Wave attenuation occurs due to absorption, scattering, geometric spreading
• Reflection, refraction, diffraction happen at medium boundaries/obstacles

Frequency, pitch, amplitude, and loudness

Frequency and pitch perception

• Pitch describes subjective perception of sound frequency
• Higher frequencies correspond to higher perceived pitches
• Human hearing range spans approximately 20 Hz to 20,000 Hz
• Pitch perception follows logarithmic relationship to frequency
• Equal-loudness contours (Fletcher-Munson curves) show frequency-dependent loudness perception
• Factors affecting pitch perception include intensity, duration, harmonics

Amplitude and loudness measurement

• Loudness represents subjective perception of sound intensity
• Amplitude of sound wave correlates with perceived loudness
• Decibel (dB) scale measures sound intensity levels logarithmically
• 10 dB increase equates to 10-fold increase in sound intensity
• Weber-Fechner law describes logarithmic relationship between perceived loudness and intensity
• Factors influencing loudness perception include duration, frequency, background noise

Longitudinal vs transverse waves

Longitudinal wave characteristics

• Particle displacement parallel to wave propagation direction
• Compressions (high pressure) and rarefactions (low pressure) form
• Propagate through all states of matter (solids, liquids, gases)
• Primary wave type for sound in fluids
• Faster propagation speed compared to transverse waves in same medium
• Examples include sound waves in air, P-waves in earthquakes

Transverse wave characteristics

• Particle displacement perpendicular to wave propagation direction
• Crests (peaks) and troughs (valleys) form
• Generally limited to solids and liquid surfaces
• Secondary wave type for sound in solids
• Slower propagation speed compared to longitudinal waves in same medium
• Examples include waves on a string, S-waves in earthquakes

Sound wave generation and propagation

Sound generation mechanisms

• Vibrating sources initiate sound waves (vocal cords, speaker diaphragms)
• Alternating compression and rarefaction regions form in surrounding medium
• Vibration frequency determines produced sound frequency
• Vibration amplitude influences sound wave amplitude
• Resonance amplifies sound production in many instruments (guitar strings)
• Harmonics contribute to timbre and richness of sound

Propagation through various media

• Gases and liquids transmit sound via molecular collisions
• Solids propagate sound through atomic/molecular vibrations in lattice structure
• Speed of sound varies with medium properties (density, temperature, elastic modulus)
• Sound speed in air (at 20°C): approximately 343 m/s
• Sound speed in water: approximately 1,480 m/s
• Sound speed in steel: approximately 5,960 m/s
• Impedance mismatches at medium interfaces cause reflection/transmission