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Sound travels as a wave through a medium, such as air. These waves are typically longitudinal waves, meaning the particles of the medium vibrate parallel to the direction the wave is traveling. This vibration causes areas of higher and lower pressure, which we call compression and rarerfaction, respectively.
Compression occurs when the particles in the medium are squeezed together, resulting in a higher density and higher pressure. This is the region of maximum intensity in a sound wave.
Rarerfaction occurs when the particles in the medium are spread apart, resulting in a lower density and lower pressure. This is the region of minimum intensity in a sound wave.
| Region | Particle Density | Pressure |
|---|---|---|
| Compression | High | High |
| Rarefaction | Low | Low |
As a sound wave propagates, it alternates between regions of compression and rarefaction. The frequency of these compressions and rarefactions determines the pitch of the sound. Higher frequency means more compressions and rarefactions per second, resulting in a higher pitch. The amplitude of the compression and rarefaction determines the loudness of the sound. Larger amplitude means greater pressure variations, resulting in a louder sound.
The speed of sound depends on the properties of the medium. In general, sound travels faster in denser and stiffer materials. The speed of sound ($v$) can be calculated using the following equation:
$$v = \frac{f \times \lambda}{T}$$Where:
Compression and rarefaction are fundamental to how we perceive sound. The rapid alternating pressure variations are what our ears detect and interpret as sound.