Longitudinal waves oscillate by particles moving back and forth about their individual equilibrium positions.
Understanding Longitudinal Wave Oscillation
In a longitudinal wave, unlike some other wave types, the individual particles of the medium do not travel along with the wave itself. Instead, the particles undergo a specific type of motion as the wave passes through.
Based on the reference provided:
The particles do not move down the tube with the wave; they simply oscillate back and forth about their individual equilibrium positions.
This key characteristic defines how the medium oscillates in response to a longitudinal wave.
Particle Motion vs. Wave Motion
It's crucial to distinguish between the motion of the individual particles and the motion of the wave itself. The reference clarifies that the particles do not move down the tube (or through the medium) with the wave. Their movement is localized. The wave's motion is observed as the movement of the disturbed region, often seen as areas of compression or expansion.
Pick a single particle and watch its motion. The wave is seen as the motion of the compressed region (ie, it is a pressure wave), which moves from left to right.
The wave propagates through the medium, transferring energy, but the particles oscillate in place around their starting points.
The Nature of the Oscillation
The oscillation of particles in a longitudinal wave is characterized by movement parallel to the direction of wave propagation. If the wave is moving horizontally, the particles oscillate horizontally. If the wave is moving vertically, the particles oscillate vertically. The oscillation is described as "back and forth about their individual equilibrium positions". This means each particle has a central, resting position, and as the wave passes, it moves away from this position in one direction, then back through it, then away in the opposite direction, and finally back to its equilibrium position, repeating this cycle.
Examples of Longitudinal Waves
Common examples illustrate this back-and-forth oscillation:
- Sound Waves: When you speak or a speaker plays music, air particles oscillate back and forth, creating areas of compression (higher pressure) and rarefaction (lower pressure) that travel as sound.
- Seismic P-waves: These are primary waves generated by earthquakes. They cause the ground to move back and forth parallel to the direction the wave is traveling.
- Waves in a Slinky: If you push and pull one end of a Slinky, you can create a longitudinal wave where the coils compress and stretch as the wave moves along the Slinky.
Understanding this specific back and forth oscillation of particles around their equilibrium positions is fundamental to grasping the nature of longitudinal waves.
