Ponderomotive Forces, Stokes Drift, and Momentum in Acoustic and Electromagnetic Waves

TL;DR

This paper uncovers universal relationships between ponderomotive forces, Stokes drift, and wave momentum in classical wave physics, applicable to both acoustic and electromagnetic waves, enhancing understanding of wave-medium interactions.

Contribution

It establishes simple, universal expressions linking ponderomotive force, Stokes drift, and wave momentum across different wave types and media.

Findings

Unified expressions for ponderomotive force, Stokes drift, and wave momentum.

Applicable to both acoustic and electromagnetic waves in inhomogeneous fields.

Provides insights into wave-medium interaction dynamics.

Abstract

We reveal universal connections between three important phenomena in classical wave physics: (i) the ponderomotive force acting on the medium particles in an oscillatory wavefield, (ii) the Stokes drift of free medium particles in a wave field, and (iii) the canonical wave momentum in a medium. We analyse these phenomena for (a) longitudinal sound waves in a gas or fluid and (b) transverse electromagnetic waves interacting with electrons in a plasma or metal. In both cases, assuming quasi-monochromatic yet arbitrarily inhomogeneous wavefields, the connections between the ponderomotive force, Stokes drift velocity, kinetic energy, and canonical wave momentum carried by the medium particles are given by the same simple expressions. This sheds light on the nature of these phenomena, their fine interplay, and can be useful for applications to dynamical transport phenomena in various types of waves.