Surface tension - Solid objects or reeds possess inherent tension but strings or membranes must first be stretched to sustain vibration.

Medium of transmission - Sound cannot be transmitted in a vacuum.

Air or water - Water is a more efficient transmitter of sound compared to air as sound travels faster in water.

More dense - Condensation.

Less dense - Rarefraction.

Human ear - The inner ear contains minute hair (cilia) of graduated sizes that respond to different speeds of sound vibrations transmitted by the eardrum. The network of cilia receptors is directly connected to the nervous system where the signals are processed.

Sound wave - An example of longitudinal vibration.

Musical sounds - A musical sound is called a tone.

Cycles - One complete up-and-down movement of the sound source vibration is called a cycle.

Hertz (Hz) are named after Heinrich Hertz (1857-1894) who generated and detected electromagnetic waves across the length of his laboratory on a wavelength of approximately one meter. To detect electromagnetic waves Hertz used a simple form of oscillator which he called a 'resonator'. Cycles per second (cps) are now expressed as Hz, i.e. 800 Hz, rather than 800 cps.

Harmonics are a combination of notes whose frequencies are related by simple whole number ratios. A harmonic series is a set of frequencies which are successive multiples of the fundamental (or 1st harmonic). For example, the set of frequencies 100, 200, 300, 400, 500 Hz is a harmonic series whose fundamental is 100 Hz and whose 5th harmonic is 500 Hz. In general, the nth harmonic of a series has a frequency which is n times the fundamental frequency.

Tone - The quality of a musical sound. An oboe might be described as producing a 'reedy' tone whereas a flute produces a 'mellow' tone.

Node - Point of no displacement. Because the ends of the string are attached and fixed in place to the guitar's structure — the bridge at one end and the frets at the other — the ends of the string are unable to move.

Anti-node - Location where constructive interference continually occurs and where the displacement is maximum.

Stringed instruments - For example, violin, cello, guitar, harp, double bass.

Tension - Amount of force used to stretch the string.

Wind instruments - For example, flute, clarinet, trumpet, trombone, saxophone.

Length of the column - Longer columned instruments generally make a lower sound and shorter columned instruments make a higher sound.

Percussion instruments - For example, drum, triangle, cymbals, xylophone.