(WVS) Types of Mechanical Waves: Longitudinal Waves Lesson

Types of Mechanical Waves

Longitudinal Waves

In contrast to transverse waves, some waves (such as sound waves) are longitudinal. In a longitudinal wave, the particles vibrate parallel to the direction the wave is traveling in.

A longitudinal wave can be shown using a slinky spring; have a look at the animation below:

The information contained in a longitudinal wave comes down to the question 'how close together are the coils of the spring?' At rest, the coils are a certain distance apart, and when the end of the slinky is shaken ( along its length) then a compressed region travels along.

The picture below shows a particle model of a longitudinal wave - it could for instance represent a bunch of air molecules in the presence of a sound wave. The air molecules vibrate in the direction of wave travel and form a series of compressions (high pressure) and rarefactions (low pressure), where the molecules are squashed together and pulled apart respectively.

Longitudinal Waves description Links to an external site.

Parts of a Longitudinal Waves

Instead of crests and troughs as seen in transverse waves, longitudinal waves have compressions and rarefactions. In longitudinal waves, there are regions where the medium is compressed and other regions where the medium is spread out. The region where the medium is compressed is known as a compression and the region where the medium is spread out is known as a rarefaction.

Wavelength, amplitude, frequency, and period are also measured in longitudinal waves just as they are in transverse waves. However, instead of measuring to successive crests in transverse waves, measuring to successive compressions should be done in longitudinal waves as seen in the image below.

Sound waves are the most common longitudinal wave we encounter.  Watch the following videos on Sound Waves to review the information above as well as listen to various frequency sound waves. In the video, you will also see how our ear works to hear sound waves.  

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