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Published byMatteo Herder Modified over 2 years ago

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Sine and Cosine are the y and x components of a point on the rim of a rotating wheel

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Degree and radians on the unit circle s (m) = r (m) * θ (radians) arclength = radius * radians

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Periodic Function

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Sinusoidal wave Amplitudes

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Wavelength (meters) Wavelength defined between any two points on wave that are one cycle apart (2*pi radians). e.g., Peaks Zeros crossing Troughs Sin(θ) where θ is an point. Wavelength of a sine wave, λ, can be measured between any two points with the same phase, such as between crests, or troughs, or corresponding zero crossings as shown.sine wavephasezero crossings

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Wave Period T (s) and Linear Frequency 1/T (s -1 ) Wave parameters T: wave period (s) λ: wave length (m) f=1/T : linear frequency 1 (2π /s -1 or cycles/s) Wave Velocity or Speed: v (m/s) = λ/T = λ * f Angular wave number: k = 2π/ λ Angular frequency: ω = 2π/ T = 2π*f Wave solution: u(x,t) = A * sin( k*x – ω *t ) (m) The period of a wave is the time interval for the wave to complete one cycle (2*pi radians). What is this waves period?

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Wave snapshot in space and time

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F(x,t) amplitude in space/time Wavelength Wave period

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Translation (space or time) of Sinusoidal wave Horizontal axis units are radians/2*pi. if f(θ=w*t) = sin( w*t ) = sin( 2π*(t/T) ) >> t=T >> sin(2 π) if f(θ=k*x) = sin( k*x ) = sin( 2π*(x/λ) ) >> x= λ >> sin(2 π)

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Phase of sinusoidal wave Three phase power: three sinusoids phase separated by 120 ⁰.

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Phase advance/delay and Unit circle Note minus sign in phase argument. The red sine phase is behind (negative) the blue line phase; hence, red sin function leads the blue sin function.

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Wavefront: where and what is it ?

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Pulse wave versus Sinusoidal wave A pulse is a compact disturbance in space/time. A sinusoidal wave is NOT compact, it is everywhere in space/time. A pulse can be ‘built’ up mathematically as a sum of sinusoidal waves.

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Superposition of wave pulses Which is the space (x) axis and which the time (t) axis?

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Waves move KE/PE energy (not mass) in time

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Longitudinal (P) vs. Transverse (S) waves: vibration versus energy transport direction

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Water and Rayleigh waves particle motions Elastic medium Rayleigh surface wave Synchronized P-SV motions Retrograde Circular particle motion Acoustic medium (water) Prograde circular particle motion

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Two different wavelength waves added Together: beating phenomena Two 1-dimensional wave pulse traveling And superimposing their amplitudes

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Huygen’s wavelets: secondary wavefronts propagated to interfere constructively and destructively to make new time advanced wavefront

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Standing waves on a string. Fixed endpoint don’t move; wave is trapped.

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Harmonic motion: two forces out of phase A mechanical wave propagates a pulse/sinusoid of KE+PE energy because the inertial forces load the springs by pushing and pulling on the springs which permits the wave energy to propagated in time.

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