There are two main types of wave motion for mechanical waves. These are longitudinal waves and transverse waves.
Sound waves are longitudinal waves.
What is Compression and Rarefaction?
Longitudinal waves means that the displacement of particles progresses in the same direction as the wave.
The longitudinal waves are manifested in a series of compressions and rarefactions.
Compression occurs when the energy from the sound source pushes the molecules towards each other, resulting in a decrease in the distance between the particles of the medium.
The opposite of compression, rarefaction is characterized by an increase in the distance between the particles of the medium.
This results in a series of compression and expansions that we know as sound waves. These compressions and expansions can take place thousands of times per second.
The sound waves carry information away from their source to reach your ear drums and brain — and we then perceive them as sound.
This rate that these compressions and rarefactions take place is known as the sound wave’s frequency. How fast or slow these waves occur, i.e. their frequency, then gets perceived by us as different pitches.
Speed of sound
Sound travels at different speeds depending on several factors such as temperature, humidity and elevation from sea level. In general terms:
- at 20°C (room temperature), air will transmit sound at 343 m/s (1125 ft/s)
- at 40°C (hotter than room temperature), air will transmit sound at 1100 m/s or 3372 ft/s