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A sound wave is often called a pressure wave because there are regions of high and low pressure established in the medium through which the sound wave travels. The regions of high pressure are known as ____ and the regions of low pressure are known as ____.
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Definition of Compression and Rarefactions:
A compression is a region within a medium in which particles of that medium are smooshed together or compressed. A rarefaction is a region within a medium in which particles of that medium are pulled apart or spread out.
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The vibration of particles of the medium about a fixed position results in compressions and rarefactions in the space surrounding the source. The compressions are high density regions and the rarefactions are low density regions. When the density of particles within any given region is high, the pressure associated with that region of space is high as well. Conversely, when the density of particles is relatively low, the pressure is relatively low as well. Thus, compressions are regarded as high pressure regions of space and rarefactions are considered low pressure regions of space.
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Most students readily think of crests and troughs at the mention of the idea of waves. The picture of a water wave or a slinky wave with its high points (crests) and low points (troughs) is ingrained in our mind. These crest and trough positions are common for transverse waves in which particles of the medium vibrate in a direction perpendicular to the wave motion. But don't be fooled! Sound waves are not transverse waves and do not result in the formation of crests and troughs. Sound waves are longitudinal waves. In a longitudinal wave, particles of the medium do not vibrate perpendicular to the direction that the medium vibrate. As such, crests (large displacements abovethe resting position) and troughs (large displacements in the opposite direction). Sound waves produce compressions and rarefactions as a result of the longitudinal motion of the particles of the medium.
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