  In easy-plane ferromagnets, we show that the interplay between a domain wall
and a spin wave packet can be formulated as the collision of two massive
particles with a gravity-like attraction. In the presence of magnetic
dissipation, the domain wall mimics a particle subject to viscous friction,
while the spin wave packet resembles a particle of variable mass. Due to
attractive nature of the interaction, the domain wall acquires a backward
displacement as a spin wave packet penetrating the domain wall, even though
there is no change in momentum of the wave packet before and after penetration.
