Final answer:
When a longitudinal wave travels through a spring, the coils move parallel to the direction of wave propagation. This movement is characterized by regions of compression and rarefaction, which cause the particles of the medium to oscillate around their equilibrium positions.
Step-by-step explanation:
When a longitudinal wave passes through a spring, each coil of the spring will move in the same direction as the wave propagation. If you were to tie a ribbon to the middle of a spring hanging from the ceiling and flick the end of the spring, you would observe that the ribbon moves back and forth in a direction that is parallel to the spring. This motion is due to the alternating regions of compression and rarefaction that pass through the spring, causing the particles of the medium (in this case, the coil to which the ribbon is attached) to oscillate back and forth around their equilibrium positions. Setup of a longitudinal wave is achieved when the end of the spring is flicked back and forth continuously along the axis of the spring, creating a train of pulses that move through the spring.
The disturbance you observe moves in the same direction as the pull on the spring, suggesting that the energy transfer and the oscillation of the spring's particles are occurring in parallel. This is a key characteristic of longitudinal waves, distinguishing them from transverse waves where the medium's movement is perpendicular to the direction of the wave's propagation. In the case of a slinky spring laid out on a table, flicking it back and forth would set up a longitudinal wave, with the coils moving parallel to the direction of the wave's travel, which represents the direction in which you flick the spring.