Sound (Physics)

Recall cards on sound as a longitudinal disturbance of matter that travels outward through a medium. Compressions and rarefactions, the sinusoidal pressure and displacement variations and their quarter-cycle phase difference, and the wave-speed relation v = omega/k = lambda*f. The speed of sound: about 331 m/s in dry air at 0 C, 343 m/s at 20 C, its dependence on absolute temperature v = 331*sqrt(T/273 K), and the forms v = sqrt(Y/rho) in a solid rod and v = sqrt(gamma R T/M) in an ideal gas. Sound intensity I = P/A, the inverse-square falloff, the pressure-amplitude relation, the threshold of hearing 10^-12 W/m^2, and the decibel scale beta = 10 log10(I/I0). Standing sound waves and normal modes: nodes and antinodes, tubes open at both ends (all harmonics, lambda_1 = 2L) versus closed at one end (odd harmonics only, lambda_1 = 4L), fundamentals, overtones, and harmonics. Sources of musical sound and timbre, the end correction, beats and the beat frequency |f1 - f2|, the Doppler effect for moving source and moving observer, and shock waves, the Mach number, the sonic boom, and the shock-cone half-angle sin(theta) = 1/M.