Resources | Subject Notes | Physics
Sound is a mechanical wave, meaning it requires a medium (like air, water, or solids) to travel. Unlike transverse waves (like light), sound waves travel through vibrations of the particles in the medium. This vibration is longitudinal.
In a longitudinal wave, the particles of the medium vibrate parallel to the direction in which the wave is traveling.
Sound waves are typically created by a vibrating object. For example, when a speaker vibrates, it causes the air molecules near it to vibrate. These vibrations are then passed on to adjacent air molecules, and so on, creating a chain of compressions and rarefactions.
| Characteristic | Description |
|---|---|
| Compression | A region where the particles of the medium are close together. |
| Rarefaction | A region where the particles of the medium are spread out. |
A sound wave consists of alternating compressions and rarefactions. The distance between two consecutive compressions (or two consecutive rarefactions) is called the wavelength (represented by λ). The number of complete wavelengths that pass a point in a given time is the frequency (represented by f).
The speed of a longitudinal wave (including sound) is related to its wavelength and frequency by the following equation:
$$v = f \times \lambda$$
Where:
Imagine a slinky. If you push and pull one end of the slinky along its length, you create a wave where the coils themselves move back and forth parallel to the direction the wave is traveling. This is analogous to how sound waves travel.
The longitudinal nature of sound waves is crucial for how we hear. Our eardrums vibrate in response to the compressions and rarefactions of sound waves, and these vibrations are then interpreted by our brain as sound.