Sound Concepts

Sound is a longitudinal wave. A sound is produced when vibrating sources make alternating areas of high and low pressure in air or some other medium.
The speed of sound is found by multiplying wavelength times frequency.
The speed of sound varies with the material. The density of the material and the compressibility of the material affect the speed of sound.
For gases, the speed of sound varies significantly with temperature.
Sound does not exist travel in a vacuum.
The Doppler effect occurs when the distance between a wave source and an observer is changing. If the distance is becoming less, the frequency of the waves increases. If the distance is increasing, the frequency decreases.
A "shock wave" occurs when a wave source is traveling faster than the speed of the waves it produces. The shock wave is very many crests added together in constructive interference. Shock waves produced by fast-moving aircraft are called sonic booms. A shock wave is analogous to the bow wave of a boat.
What musicians call the pitch of a sound is what scientists call the frequency of the sound wave.
What listeners call the loudness of a sound is what scientists call the amplitude of the sound wave.