- 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.