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| {{redirect|Sinusoid|the blood vessel|Sinusoid (blood vessel)}}
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| [[File:Sine and Cosine.svg|thumb|400px|right|The graphs of the sine and [[Trigonometric functions#cosine|cosine]] functions are sinusoids of different phases.]]
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| The '''sine wave''' or '''sinusoid''' is a [[curve|mathematical curve]] that describes a smooth repetitive [[oscillation]]. It is named after the function [[sine]], of which it is the [[graph of a function|graph]]. It occurs often in pure and applied [[mathematics]], as well as [[physics]], [[engineering]], [[signal processing]] and many other fields. Its most basic form as a function of time (''t'') is''':'''
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| :<math>y(t) = A\sin(2 \pi f t + \phi) = A\sin(\omega t + \phi)</math>
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| where:
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| * ''A'', the ''[[amplitude]]'', is the peak deviation of the function from zero.
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| * ''f'', the ''[[frequency|ordinary frequency]]'', is the ''[[Real number|number]]'' of oscillations (cycles) that occur each second of time.
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| * ''ω'' = 2π''f'', the ''[[angular frequency]]'', is the rate of change of the function argument in units of [[radian]]s per second
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| * ''φ'', the ''[[Phase (waves)|phase]]'', specifies (in radians) where in its cycle the oscillation is at ''t'' = 0.
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| ** When ''φ'' is non-zero, the entire waveform appears to be shifted in time by the amount ''φ''/''ω'' seconds. A negative value represents a delay, and a positive value represents an advance.
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| {{Listen|filename=220 Hz sine wave.ogg|title=Sine wave|description=2 seconds of a 220 Hz sine wave}}
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| [[File:Simple harmonic oscillator.gif|right|frame|The oscillation of an undamped spring-mass system around the equilibrium is a sine wave.]]
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| The sine wave is important in physics because it retains its waveshape when added to another sine wave of the same frequency and arbitrary phase and magnitude. It is the only periodic waveform that has this property. This property leads to its importance in [[Fourier analysis]] and makes it acoustically unique.
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| == General form ==
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| In general, the function may also have''':'''
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| * a spatial variable ''x'' that represents the ''position'' on the dimension on which the wave propagates, and a characteristic parameter ''k'' called [[wavenumber]] (or angular wave number), which represents the proportionality between the angular frequency ω and the linear speed ([[phase velocity|speed of propagation]]) ν
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| * a non-zero center amplitude, ''D''
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| which is
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| :<math>y(x,t) = A\sin(kx -\omega t + \phi ) + D\,</math>, if the wave is moving to the right
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| :<math>y(x,t) = A\sin(kx + \omega t + \phi ) + D\,</math>, if the wave is moving to the left
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| <ref>Resnick Halliday Walker, Fundamentals of Physics</ref>
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| The wavenumber is related to the angular frequency by''':'''.
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| :<math> k = { \omega \over v } = { 2 \pi f \over v } = { 2 \pi \over \lambda }</math>
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| where λ is the [[wavelength]], ''f'' is the [[frequency]], and ''v'' is the linear speed.
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| This equation gives a sine wave for a single dimension, thus the generalized equation given above gives the amplitude of the wave at a position ''x'' at time ''t'' along a single line.
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| This could, for example, be considered the value of a wave along a wire.
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| In two or three spatial dimensions, the same equation describes a travelling [[plane wave]] if position ''x'' and wavenumber ''k'' are interpreted as vectors, and their product as a [[dot product]].
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| For more complex waves such as the height of a water wave in a pond after a stone has been dropped in, more complex equations are needed.
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| == Occurrences ==
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| [[File:ComplexSinInATimeAxe.gif|thumb|400px|Illustrating the cosine wave's fundamental relationship to the circle.]]
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| This [[wave]] pattern occurs often in nature, including [[ocean surface wave|ocean waves]], [[sound]] waves, and [[light]] waves.
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| A [[cosine]] wave is said to be "sinusoidal", because <math>\cos(x) = \sin(x + \pi/2),</math>
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| which is also a sine wave with a phase-shift of π/2. Because of this "[[head start (positioning)|head start]]", it is often said that the cosine function ''leads'' the sine function or the sine ''lags'' the cosine.
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| The human [[ear]] can recognize single sine waves as sounding clear because sine waves are representations of a single [[frequency]] with no [[harmonics]]; some sounds that approximate a pure sine wave are [[whistling]], a [[crystal glass]] set to vibrate by running a wet finger around its rim, and the sound made by a [[tuning fork]].
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| To the human ear, a sound that is made of more than one sine wave will have perceptible [[harmonics]]; addition of different sine waves results in a different waveform and thus changes the [[timbre]] of the sound. Presence of higher harmonics in addition to the fundamental causes variation in the timbre, which is the reason why the same musical [[note]] (the same frequency) played on different instruments sounds differently. On the other hand, if the sound contains aperiodic waves along with sine waves (which are periodic), then the sound will be perceived "noisy" as [[Noise (acoustic)|noise]] is characterized as being aperiodic or having a non-repetitive pattern.
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| == Fourier series ==
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| [[File:Waveforms.svg|thumb|400px|Sine, [[square wave|square]], [[triangle wave|triangle]], and [[sawtooth wave|sawtooth]] waveforms]]
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| {{main|Fourier analysis}}
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| In 1822, [[Joseph Fourier]], a French mathematician, discovered that sinusoidal waves can be used as simple building blocks to describe and approximate any periodic waveform including [[square wave]]s. Fourier used it as an analytical tool in the study of waves and heat flow. It is frequently used in [[signal processing]] and the statistical analysis of [[time series]].
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| ==Traveling and standing waves==
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| Since sine waves propagate without changing form in distributed linear systems, they are often used to analyze [[wave]] propagation. Sine waves traveling in two directions can be represented as
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| :<math>y(t) = A \sin(kx - \omega t)</math> and <math>y(t)= A \sin(kx + \omega t).</math> | |
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| When two waves having the same amplitude and frequency, and traveling in opposite directions, [[Superposition principle|superpose]] each other, then a [[standing wave]] pattern is created. Note that, on a plucked string, the interfering waves are the waves reflected from the fixed end points of the string.Therefore, standing waves occur only at certain frequencies, which are referred to as resonant frequencies and are composed of a fundamental frequency and its higher harmonics. The resonant frequencies of a string are determined by the length between the fixed ends and the [[Tension (physics)|tension]] of the string.
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| == References ==
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| {{reflist}}
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| == See also ==
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| * [[Crest (physics)]]
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| * [[Fourier transform]]
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| * [[Harmonic series (mathematics)]]
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| * [[Harmonic series (music)]]
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| * [[Helmholtz equation]]
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| * [[Instantaneous phase]]
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| * [[Pure tone]]
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| * [[Simple harmonic motion]]
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| * [[Sinusoidal model]]
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| * [[Wave (physics)]]
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| * [[Wave equation]]
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| ==Further reading==
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| *{{cite web |url=http://www.encyclopediaofmath.org/index.php/Sinusoid |work=Encyclopedia of Mathematics |title=Sinusoid |publisher=Springer |accessdate=December 8, 2013}}
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| [[Category:Trigonometry]]
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| [[Category:Wave mechanics]]
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| [[Category:Waves]]
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| [[Category:Waveforms]]
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