Waves Waves are “a disturbance that transfers energy”. Some waves can only move through matter. The matter they move through is called a “medium”; and these waves are called “mechanical waves”. Some waves can move through a vacuum; these waves are called “electro- magnetic waves”; electromagnetic waves can also move through matter. When mechanical waves move through a medium, the medium doesn’t change locations. The particles of the medium move as the wave passes, but they return to their original location.

Types of Mechanical Waves Transverse waves – the particles of the medium vibrate at right angles to the direction of wave motion Longitudinal waves – the particles of the medium vibrate parallel to the direction of wave motion Surface waves (which occur at the boundary of a medium instead of within it) – the particles of the medium travel in a circular path

Parts of a Wave Wave pulse – a single piece of wave energy (non-periodic, non-repeating) Periodic wave – a wave produced by a repetitive vibration (periodic) Transverse waves have “crests” and “troughs” – high points and low points [graphed as “displacement” as a function of position] Longitudinal waves have “compressions” and “rarefactions” – regions of high density and regions of low density [graphed as “density” as a function of position]

Wave Properties Wavelength – the distance between adjacent similar points along a periodic wave (usually crest-to-crest, but also trough-to-trough, etc.) Amplitude – the magnitude of displacement from the “at rest” position; amplitude is related to the amount of energy – the “volume” of your stereo Period – the time taken by one wavelength (cycle) to pass a certain point Frequency – the number of wavelengths that pass a certain point in a given amount of time [frequency = period-1] Units: Hertz (Hz) “cycles per second” Wave Speed – how fast the wave moves v = f x λ (frequency x wavelength)

Wave Interference When more than one wave is traveling through a particular location, the waves “interfere” with each other – the displacements of the two waves combine with each other into a single wave When two positive displacements (or two negative displacements) combine, the resulting displacement has a greater magnitude – this is called “constructive interference” When a positive displacement and a negative displacement combine, the resulting displacement has a lesser magnitude – this is called “destructive interference”

Standing Waves When a wave is reflected from a fixed boundary and its frequency meets certain conditions, a “standing wave” is created – the pattern of the wave is stationary Certain parts of a standing wave have complete destructive interference; these parts have no displacement – they are called “nodes” Other parts have complete constructive interference; these part have the greatest amount of displacement – they are called “antinodes” The two ends of a standing wave are always nodes; and the number of nodes is always one greater than the number of antinodes