Longitudinal Wave

Longitudinal wave: medium particles oscillate PARALLEL to direction of wave propagation.

Examples: sound in air/water, P-waves (compression seismic waves), waves along a Slinky.

Compressions and rarefactions alternate along the wave direction.

Speed in a fluid: v = √(B/ρ), where B = bulk modulus, ρ = density.

Sound in air at 20°C: v ≈ 343 m/s. In water: v ≈ 1500 m/s. In steel: v ≈ 5000 m/s.

CANNOT be polarised — oscillation direction is set by propagation.

Can propagate in solids, liquids, gases — wherever pressure can transmit force.

Same wave equation y(x,t) = A·sin(kx − ωt) but y is now particle displacement along x.