```                               WAVE AND WAVE MOTION
Waves                                                   Frequency (f): Number of oscillations
performed by a particle per unit time.
    It is a vibration or disturbance in space.
    A medium is the substance that all sound           Wavelength (λ): For a progressive wave, it is
waves travel through and need to have in           the distance between any two successive
order to move.                                     particles that are in phase, e.g. it is the distance
between 2 consecutive crests or 2 troughs.
Types of Waves
Wave speed (v): The speed at which the
1. Longitudinal Wave - A fixed point will               waveform travels in the direction of the
move parallel with the wave motion.                propagation of the wave.
[Compression- an area of high molecular
density and pressure; Rarefaction - an area        Wave front: A line or surface joining points
of low molecular density and pressure]. It         which are at the same state of oscillation, i.e.
can passes through liquids and gasses.             in phase, e.g. a line joining crest to crest in a
2. Transverse Wave - A fixed point will                 wave.
move perpendicular with the wave motion.
Wave parts (recall demo for simple                 Ray: The path taken by the wave. This is used
harmonic        motion)-     crest,   trough,      to indicate the direction of wave propagation.
wavelength, amplitude, frequency, period.          Rays are always at right angles to the wave
It requires a material to be solid to              fronts (i.e. wave fronts are always
propagate.                                         perpendicular to the direction of propagation).
3. Surface waves - particles travel in a
circular motion. These waves occur at              Sound Wave
interfaces. Examples include waves in the
ocean and ripples in a cup of water.                  Sound waves exist as variations of
4. Electromagnetic waves (including light)                  pressure in a medium such as air.
can move through a vacuum.                          They are created by the vibration of an
5. Physical waves require matter through                    object, which causes the air surrounding it
which to propagate. Physical waves are                 to vibrate.
further distinguished by the phases of              The vibrating air then causes the human
matter through which they can move.                    eardrum to vibrate, which the brain
interprets as sound.
Wave Motion                                              The scientific study of sound waves is
known as acoustics.
It transfers energy from one point to another,          Facts about Sound
often with no permanent displacement of the              Dogs can hear sound at a higher frequency
particles of the medium - that is, with little or           than humans, allowing them to hear noises
no associated mass transport.                               that we can’t.
 Sound can’t travel through a vacuum (an
Displacement (y): Position of an oscillating                area empty of matter).
particle from its equilibrium position.                  The speed of sound is around 767 miles
per hour (1,230 kilometres per hour).
Amplitude (y0 or A): The maximum                         When traveling through water, sound
magnitude of the displacement of an                         moves around four times faster than when
oscillating particle from its equilibrium                   it travels through air.
position.                                                The sound of thunder is produced by
rapidly heated air surrounding lightning
Period (T): Time taken for a particle to                    which expands faster than the speed of
undergo one complete cycle of oscillation.                  sound.
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