The primary motion of particles in a longitudinal wave is?

In a longitudinal wave, the primary motion of particles is parallel to the direction of wave propagation. This means that as the wave travels through a medium, the particles of that medium oscillate back and forth in the same direction as the wave moves. When a compression occurs, particles are pushed together, and during a rarefaction, they spread apart. This oscillation results in areas of high pressure (compressions) and low pressure (rarefactions) along the pathway of the wave, which is characteristic of longitudinal waves, such as sound waves in air.

The other options refer to different types of wave motion. For instance, elliptical motion pertains to waves where particles move in circular paths combined vertically and horizontally, which is typical in surface waves such as those found in water. Perpendicular motion describes transverse waves, where particles move at right angles to the direction of wave propagation, such as in light waves or waves on a string. Random motion does not correspond to the organized oscillation found in waves. Understanding these distinctions highlights the unique properties of longitudinal waves and the nature of particle behavior within them.