Waves, Oscillations & Acoustics — 53 Terms Defined

Absorption Coefficient Waves, Oscillations & Acoustics Dimensionless The fraction of incident sound energy absorbed by a material surface rather than reflected. α = I_absorbed / I_incident (0 ≤ α ≤ 1)

Acoustic Impedance Waves, Oscillations & Acoustics Pa·s/m (Rayls) The physical opposition offered by a medium to sound wave flow, defined as ratio of acoustic pressure to particle velocity. Z = ρ v_sound

Acoustic Power Waves, Oscillations & Acoustics W The total sound energy emitted by an acoustic source per unit time in all directions. P_ac = ∫ I · dA = 4π r² I

Acoustic Resonance Waves, Oscillations & Acoustics Hz The amplification of sound waves within a hollow cavity or tube when driven at frequencies matching cavity standing wave modes. f_n = n v / (2 L)

Angular Frequency Waves, Oscillations & Acoustics rad/s A scalar measure of rotation or oscillation rate expressed in radians per unit time. ω = 2π f = 2π / T

Beats Waves, Oscillations & Acoustics Hz The periodic volume fluctuation or throbbing sound produced by the interference of two sound waves with slightly different frequencies. f_beat = |f1 - f2|

Closed Organ Pipes Waves, Oscillations & Acoustics Hz An acoustic pipe closed at one end and open at the other, having a displacement node at the closed end and an antinode at the open end. f_n = n v / (4 L) (n = 1, 3, 5, ...)

Compound Pendulum Waves, Oscillations & Acoustics s A rigid body suspended from a fixed horizontal axis that oscillates under gravity about a pivot point. T = 2π √(I / (m g d))

Constructive & Destructive Interference Waves, Oscillations & Acoustics m The phenomenon where overlapping coherent waves combine to reinforce (constructive) or cancel (destructive) each other's amplitude. Path Diff ΔL = m λ (Constructive), ΔL = (m + ½) λ (Destructive)

Damped Oscillations Waves, Oscillations & Acoustics m Oscillatory motion whose mechanical energy and amplitude decrease exponentially over time due to dissipative forces like friction or viscosity. x(t) = A exp(-b t / 2m) cos(ω_d t + φ)

Decibel Scale Waves, Oscillations & Acoustics dB A logarithmic scale used to express sound intensity or sound pressure level relative to a reference threshold. β = 10 log10(I / I0), I0 = 10⁻¹² W/m²

Doppler Effect Waves, Oscillations & Acoustics Hz The apparent shift in observed wave frequency caused by relative motion between the wave source and the observer. f_obs = f_src (v ± v_obs) / (v ∓ v_src)

Echo Waves, Oscillations & Acoustics m A distinct reflected sound wave received at the listener's ear with sufficient time delay after the direct sound. d = v t / 2

End Correction Waves, Oscillations & Acoustics m An acoustic correction applied to resonance pipe lengths to account for displacement antinodes forming slightly outside the open pipe ends. e ≈ 0.6 r, L_effective = L + 0.6 r (One Open End)

Forced Oscillations Waves, Oscillations & Acoustics m Oscillations produced in a system subjected to a periodic external driving force. m (d²x/dt²) + b (dx/dt) + k x = F0 cos(ω t)

Frequency Waves, Oscillations & Acoustics Hz (s⁻¹) The number of complete wave cycles or vibrational repetitions occurring per unit time. f = 1 / T = v / λ

Fundamental Frequency Waves, Oscillations & Acoustics Hz The lowest natural frequency at which a standing wave pattern can be established in a vibrating system. f1 = v / (2 L) (String / Open Pipe)

Group Velocity Waves, Oscillations & Acoustics m/s The velocity at which the overall envelope shape of a wave packet travels through space, representing energy transport speed. v_g = dω / dk

Harmonics Waves, Oscillations & Acoustics Hz Resonant frequencies of a system that are integer multiples of its fundamental frequency. f_n = n f1 (where n = 1, 2, 3, ...)

Huygens-Fresnel Principle Waves, Oscillations & Acoustics N/A The wave propagation principle asserting that every point on a wavefront acts as a secondary source of spherical wavelets. New Wavefront = Envelope of Secondary Wavelets

Lissajous Figures Waves, Oscillations & Acoustics N/A Complex geometric curves traced by combining two perpendicular simple harmonic oscillations. x(t) = A sin(a t + δ), y(t) = B sin(b t)

Longitudinal Wave Waves, Oscillations & Acoustics m A wave in which medium particles oscillate parallel to the direction of wave energy propagation. s(x,t) = s_max cos(k x - ω t)

Loudness Waves, Oscillations & Acoustics Sone (or Phon) The subjective human psychological sensation of sound strength, depending on physical intensity and ear frequency response. Loudness ∝ log10(I / I0)

Mach Number Waves, Oscillations & Acoustics Dimensionless A dimensionless speed ratio equal to the speed of an object or fluid divided by local speed of sound in the surrounding medium. M = v / v_sound