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.