Good Vibes

Even prior to the annual science units on the moon phases, the identity of sound as a wave has been ingrained into every child's grey matter. Sound is a wave. Sound is a wave. Sound is a ...wait, what's a wave?

The ripples of a pond disturbed by a pebble are an example of waves. The oscillating rope below is an example of a wave. A wave is an energy-transferring disturbance in a medium, or the substance through which the wave moves. For instance, in the first example the disturbance is the rippling of the water surface and the medium is the water.

To no one's surprise, a dichotomy between types of waves exists. A sound wave would be classified as a mechanical wave, in which the particles of the medium experience motion. This is in contrast to an electromagnetic wave which requires no medium and deals with light, not sound, so we shall pay it no more heed.

Furthermore, a sound wave is further categorized as a longitudinal wave, as opposed to a transverse wave. A transverse wave is one in which the particles of the medium move perpendicular to the direction of the wave. Since a picture is worth about $300 million, a graphic is probably appropriate.

As you can see in the above GIF, the motion of the wave is quite apparently moving to the right. However, the individual components of the medium (people) are moving vertically. The water ripples and the twanged rope are both examples of transverse waves.

However, sound is not a transverse wave but a longitudinal wave in which the particles of the medium travel parallel to the wave's motion. Cue another fabulous visual by Daniel A. Russell.

Similar to the "people-wave", the motion of this wave is to the right. Unlike the previous wave, however, the motion of each individual particle is side-to-side (parallel to the motion of the wave!). Applying this model to sound, we can imagine all the black specks as various molecules in the air. The red bar on the left is a speaker which compresses the air, creating a disturbance that is propagated through the medium. This disturbance eventually reaches our eardrums, where it is captured (much like a wild gazelle) and sent to the brain to be analyzed. Therefore, sound is simply a transmitted vibration of the air.

Sources:

Knight, Randall Dewey, Brian Jones, and Stuart Field. "Traveling Waves and Sound." College Physics: A Strategic Approach. 3rd ed. N.p.: Pearson Education, n.d. N. pag. Print.

Russell, Daniel A. Multiple Wave GIFs. Digital image. Acoustics and Vibration Animations. N.p., 18 Feb. 2015. Web. 20 Oct. 2015.

"What Is a Wave?" What Is a Wave? The Physics Classroom, n.d. Web. 20 Oct. 2015.