Sound is a mechanical wave that travels through a medium (air, water, solids) by the vibration of particles. Unlike transverse waves (like waves on a string), sound waves are longitudinal – the particles move back and forth in the same direction as the wave travels.
Imagine a crowd at a stadium doing the wave. Each person stands up and sits down in sequence. The movement travels through the crowd, but the people themselves only move up and down (not sideways). Similarly, in a sound wave, the air molecules move forward and backward along the direction the sound travels.
| Parameter | Symbol | Units |
|---|---|---|
| Wavelength | \$\lambda\$ | m |
| Frequency | \$f\$ | Hz |
| Speed of Sound | \$v\$ | m s⁻¹ |
| Amplitude | \$A\$ | m or Pa |
The speed of a sound wave in a given medium is related to its frequency and wavelength by the equation:
\$v = f \lambda\$
For example, in air at 20 °C, \$v \approx 343\;\text{m s}^{-1}\$. If a note has a frequency of 440 Hz (A4), its wavelength is:
\$\lambda = \frac{v}{f} = \frac{343}{440} \approx 0.78\;\text{m}\$
Sound waves are longitudinal mechanical waves where particles oscillate parallel to the direction of propagation, creating alternating compressions and rarefactions. Their key properties—frequency, wavelength, speed, and amplitude—are linked by \$v = f \lambda\$, and they can travel through any medium that allows particle interaction.