Which of the following best describes a longitudinal wave?

A longitudinal wave is characterized by the movement of particles in the same direction as the wave is traveling. In this type of wave, areas of compression and rarefaction occur, which means that particles are pushed together (compression) and then spread apart (rarefaction) as the wave moves through a medium.

This motion results in alternating dense and less dense regions within the material through which the wave is traveling. Sound waves in air are a classic example of longitudinal waves, as the air particles oscillate back and forth in the same direction as the sound wave propagates.

The other options describe different types of wave motion: circular motion typically pertains to waves like water waves where particles move in circular paths; perpendicular motion describes transverse waves, where particles move at right angles to the direction of the wave, as seen in light waves; and independent back-and-forth motion doesn't correlate with the propagation of a wave, as it suggests a lack of coherent movement along the direction of the wave.