audio spectrum - the range of frequencies that humans are able to hear. Ideally, this ranges from as low as 20 Hz to as high as 20,000 Hz. Often, age and hearing loss prevent people from hearing the entire range. Many animals can hear frequencies outside of this range.
compression - the regions of a sound wave (or other longitudinal wave) in which the particles are "squished" together, or compressed.
decibels (dB) - the unit used to measure the relative intensity of sound. The decibel scale is logarithmic, which means that small decibel changes actually represent large differences in the intensity of a sound. The unit is named after Alexander Graham Bell, inventor of the telephone; therefore, its abbreviation includes a capital "B."
Doppler Effect - the apparent shift in frequency due to the relative motion of the source source and the listener.
frequency - the number of cycles, waves, or compressions made each second. The unit for frequency is Hertz.
Hertz (Hz) - the unit used to measure frequency. It is named after Heinrich Hertz, a scientist who studied electromagnetic waves; therefore, the unit is capitalized.
intensity - the loudness of a sound. Can be measured in units of Watts per square meter, but is often measured in units of decibels.
longitudinal - a type of wave in which the particles vibrate in the same place as the wave travels. Sound waves are longitudinal. Light and water waves are transverse.
medium - the substance that a wave travels through. For sound waves, the medium is usually air, but sound waves can also travel through liquids and solids. The medium determines how fast the sound wave travels.
noise - an undesirable sound which has no constant frequency, or an unpleasant mix of frequencies.
pitch - the highness or lowness of a tone. Depends on frequency: the higher the frequency the higher the pitch.
rarefaction - the regions of a sound wave (or other longitudinal wave) in which the particles are spread out.
source - the object which is vibrating to produce sound.
speed - how fast a sound wave travels through its given medium. Measured in meters per second. The speed of sound depends on the medium and its temperature.