Sound Wave Properties: Wavelength, Frequency, Speed

• Sound is a mechanical wave needing a medium like air, water, or solids to propagate.
• Sound cannot travel in a vacuum.
• The speed of sound depends on the medium's properties, including density and elasticity.
• Sound travels at approximately 343 meters per second in dry air at 20°C.
• Sound waves are longitudinal, with medium particles vibrating parallel to the wave's direction.
• Compressions are high-pressure regions in a sound wave.
• Rarefactions are low-pressure regions in a sound wave.
• Wavelength (λ) is the distance between successive compressions or rarefactions.
• Frequency (f) is the number of complete waves passing a point per unit time, measured in Hertz (Hz).
• Period (T) is the time for one complete wave to pass a point; it is the inverse of frequency (T = 1/f).
• Amplitude is the maximum particle displacement from equilibrium, related to sound intensity or loudness.
• The relationship between the speed of sound (v), frequency (f), and wavelength (λ) is v = fλ.
• Sound intensity (I) is the power (P) carried by a sound wave per unit area (A), measured in watts per square meter (W/m²): I = P/A.
• Sound intensity is proportional to the square of the sound wave's amplitude.
• Sound level is measured in decibels (dB) using a logarithmic scale relative to a reference intensity (I₀ = 10⁻¹² W/m²): dB = 10 log₁₀(I/I₀).
• The threshold of hearing is around 0 dB, corresponding to the reference intensity I₀.
• A 10 dB increase means a tenfold increase in sound intensity.
• Pitch is the perception of a sound's frequency.
• High-frequency sounds are high-pitched, and low-frequency sounds are low-pitched.
• Human hearing typically ranges from 20 Hz to 20,000 Hz.
• Ultrasound has frequencies above 20,000 Hz, beyond human hearing.
• Infrasound has frequencies below 20 Hz, below human hearing.
• The Doppler effect is the change in wave frequency or wavelength relative to a moving observer.
• The observed frequency increases (higher pitch) when a sound source approaches an observer.
• The observed frequency decreases (lower pitch) when a sound source moves away from an observer.
• For a moving source and stationary observer, the Doppler effect equation is f' = f (v / (v ± vs)), where f' is the observed frequency, f is the source frequency, v is the speed of sound, and vs is the source's speed. Use + when the source is moving away and - when moving towards.
• The Doppler effect is applied in radar, sonar, and medical imaging.
• Superposition is when overlapping waves' displacements combine.
• Constructive interference occurs when waves are in phase, increasing amplitude.
• Destructive interference occurs when waves are out of phase, decreasing amplitude.
• Beat frequency is the difference between two close frequencies: f_beat = |f₁ - f₂|.
• Beats are periodic amplitude variations from two interfering sound waves with slightly different frequencies.
• Resonance occurs when an object vibrates at its natural frequency.
• Natural frequency is the frequency at which an object most easily vibrates.
• Forced vibration is an object's vibration caused by an external force.
• A tube closed at one end resonates at lengths of L = (2n-1)λ/4, where n = 1, 2, 3...
• A tube open at both ends resonates at lengths of L = nλ/2, where n = 1, 2, 3...
• The fundamental frequency is the lowest resonant frequency.
• Harmonics are integer multiples of the fundamental frequency.
• Overtones are resonant frequencies above the fundamental frequency.
• Sound quality (timbre) is determined by the amplitudes of the fundamental frequency and its overtones.
• Reflection happens when a sound wave bounces off a surface.
• Echoes are sound wave reflections heard distinctly from the original.
• Reverberation is sound persistence due to multiple reflections after the original sound stops.
• Absorption converts sound energy into other forms, like heat.
• Soundproofing reduces sound transmission using specific materials and techniques.
• Diffraction is the bending of waves around obstacles or through openings.
• Sound waves diffract around corners and through doorways.
• Diffraction depends on the sound wave's wavelength and the obstacle/opening size.
• Acoustic impedance (Z) measures how difficult sound passes through a material: Z = ρv, where ρ is density and v is the speed of sound.
• Sound waves are partially reflected/transmitted between media with different acoustic impedances.
• Greater acoustic impedance differences cause greater reflection.
• Sonar (Sound Navigation and Ranging) uses sound waves to detect underwater objects.
• Ultrasound imaging uses high-frequency sound waves to image internal body structures.
• Musical instruments produce sound through vibrating strings, air columns, etc.
• Different instruments have unique sounds due to their harmonic and overtone combinations.

Explore the properties of sound waves: mechanical wave nature, speed in different mediums, compressions, rarefactions, wavelength, frequency, and amplitude. Understand how these properties define the characteristics of sound and its propagation. Sound waves are longitudinal waves.