Which type of wave has particle motion that is perpendicular to the direction of wave propagation?

A transverse wave is characterized by particle motion that is perpendicular to the direction in which the wave propagates. To visualize this, imagine a wave traveling along a string: as the wave moves horizontally, the individual segments of the string move up and down. This distinct orientation of particle movement in contrast to the direction of the wave's travel is what defines transverse waves.

In contrast, longitudinal waves, such as sound waves, involve particle motion that occurs in the same direction as the wave’s propagation, causing regions of compression and rarefaction.

Mechanical waves require a medium through which to propagate, but this trait applies to both transverse and longitudinal waves, so it does not specifically indicate their mode of particle motion. Surface waves, often seen in water, combine characteristics of both longitudinal and transverse waves, exhibiting complex motion but do not solely represent the perpendicular motion of particles.

Thus, the definition of a transverse wave aligns with the description of particle motion being perpendicular to the direction of wave propagation.