4.7.1: Transverse and Longitudinal Waves
- Page ID
- 472555
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- Understand the difference between a transverse and a longitudinal wave.
A simple wave consists of a periodic disturbance that propagates from one place to another. The wave in Figure \(\PageIndex{3}\) propagates in the horizontal direction while the surface is disturbed in the vertical direction. Such a wave is called a transverse wave or shear wave; in such a wave, the disturbance is perpendicular to the direction of propagation. In contrast, in a longitudinal wave or compressional wave, the disturbance is parallel to the direction of propagation. Figure \(\PageIndex{4}\) shows an example of a longitudinal wave. The size of the disturbance is its amplitude \(X\) and is completely independent of the speed of propagation \(v_{\mathrm{w}}\).
Waves may be transverse, longitudinal, or a combination of the two. (Water waves are actually a combination of transverse and longitudinal. The simplified water wave illustrated in Figure \(\PageIndex{2}\) shows no longitudinal motion of the bird.) The waves on the strings of musical instruments are transverse—so are electromagnetic waves, such as visible light.
Sound waves in air and water are longitudinal. Their disturbances are periodic variations in pressure that are transmitted in fluids. Fluids do not have appreciable shear strength, and thus the sound waves in them must be longitudinal or compressional. Sound in solids can be both longitudinal and transverse.
Earthquake waves under Earth’s surface also have both longitudinal and transverse components (called compressional or P-waves and shear or S-waves, respectively). These components have important individual characteristics—they propagate at different speeds, for example. Earthquakes also have surface waves that are similar to surface waves on water.
Exercise \(\PageIndex{1}\)
Why is it important to differentiate between longitudinal and transverse waves?
- Answer
-
In the different types of waves, energy can propagate in a different direction relative to the motion of the wave. This is important to understand how different types of waves affect the materials around them.
Section Summary
- A transverse wave has a disturbance perpendicular to its direction of propagation, whereas a longitudinal wave has a disturbance parallel to its direction of propagation.
Glossary
- longitudinal wave
- a wave in which the disturbance is parallel to the direction of propagation
- transverse wave
- a wave in which the disturbance is perpendicular to the direction of propagation