Write the displacement variable in the propagation of sound in air.

(N/A) In the propagation of sound in air,the displacement variable is the displacement of air molecules from their mean equilibrium position.
Let the displacement of a particle at position $x$ and time $t$ be represented by $y(x, t)$.
The equation for a plane progressive harmonic sound wave is given by:
$y(x, t) = A \sin(kx - \omega t + \phi)$
Where:
$A$ is the amplitude of the displacement of air molecules.
$k$ is the angular wave number $(k = 2\pi / \lambda)$.
$\omega$ is the angular frequency $(\omega = 2\pi f)$.
$\phi$ is the initial phase constant.
Thus,the displacement variable represents the longitudinal oscillation of air molecules along the direction of wave propagation.