Waves and Sound AP I

Definition of a wave  A disturbance that propagates from 1 place to another.  Characterized by a large transfer of energy without a large transfer of medium

Types of waves  Mechanical waves: require a medium (air, water, ropes) to travel  Electromagnetic waves: do not require a medium to travel (light, radio)

Mechanical Waves  Transverse: the displacement of the individual particles is perpendicular to the direction of propagation.

Mechanical Waves  Longitudinal: The displacement of the individual particles is parallel to the direction of propagation.

Mechanical Waves  Surface waves: the displacement of individual particles is circular (result of both transverse and longitudinal motion)

Waves in motion  Longitudinal and Transverse Wave Motion Longitudinal and Transverse Wave Motion Longitudinal and Transverse Wave Motion

Properties of waves 1. Amplitude (A): the maximum displacement from equilibrium position, measured in meters. 2. Wavelength ( λ): the distance between 2 particles that are in phase with each other, measured in meters.

Wave diagram (link) (link)

Properties of waves 3. Frequency (f): number of complete waves that pass a point in one second, measured in 1/seconds or Hertz (Hz) 4. Period (T): the time it takes for one complete wave to pass a given point, measured in seconds.

Properties of waves  Velocity of propagation (v): horizontal speed of a point on a wave as it propagates, measured in m/s.

Relationships/equations  T =1/ f or f = 1/T  v = f × λ

Phase  In-phase: when waves are synchronized (crest meets crest)  Out-of-phase: waves are not synchronized Opposite phase (180º out-of-phase): crest meets trough Opposite phase (180º out-of-phase): crest meets trough

Reflections  Fixed End: Explanation Explanation Explanation Animation Animation Animation  Open End: Explanation Explanation Explanation Animation Animation Animation  Between different mediums scroll down (What do you notice about the phases? Transmitted? Reflected?) Between different mediums Between different mediums

Principle of Superposition  Occurs when two waves travel through the same medium at the same time.  Each wave affects the medium independently.  The displacement of the medium is the algebraic sum of the displacements.  Animation Animation

Interference  Constructive: occurs when wave displacements are in the same direction (in-phase)  Destructive: occurs when wave displacement are in different directions (out-of-phase)  Animation (try at home) Animation

What is Sound?  Longitudinal  Mechanical (link) (link)  Rarefaction: low air pressure  Compression: high air pressure  module (sources of sound) module

Speed of sound  Depends on… Temperature Temperature V air = 331m/s +(0.6 m/s/ºC)*TV air = 331m/s +(0.6 m/s/ºC)*T Density/kind of medium Density/kind of medium Gases <liquids<solidsGases <liquids<solids Chart of speedsChart of speedsChart of speedsChart of speeds

Speed of sound

Pitch  How we perceive variations in frequency  Audible range 20-20,000 Hz (listen) listen Infrasonic vs. ultrasonicInfrasonic vs. ultrasonic  Most sensitive to 1,000 to 5,000Hz  Loudness can distort our perception of pitch (listen tape)  Module (pitch) Module

Doppler Effect  Variation in the frequency of sound due to the relative motion of the sound source or the listener.  Animation1 Animation1  Picture of a sonic boom Picture of a sonic boom Picture of a sonic boom  Video of sonic boom Video of sonic boom Video of sonic boom  mythbuster mythbuster

Doppler Effect Results  As an moving sound source approaches a listener the frequency (pitch) increase.  As a moving sound source passes by a listener the frequency (pitch) decreases. *Same effect if sound source is stationary and listener is moving.

Calculating Frequency change  f’ = f (v ± v R / v± v s ) f’ = new frequency f’ = new frequency f = original frequency of source soundf = original frequency of source sound v: velocity of soundv: velocity of sound v R : velocity of receiverv R : velocity of receiver v s : velocity of sourcev s : velocity of source

Resonance  Causing the vibration of an object by the influence of another vibrating body. Must match the natural frequency of vibration of the object Must match the natural frequency of vibration of the object Whole-number multiple of the natural frequency work too. Whole-number multiple of the natural frequency work too. Breaking a glass with resonance Breaking a glass with resonance Breaking a glass with resonance Breaking a glass with resonance Boy breaks glass with voice Boy breaks glass with voice Boy breaks glass with voice Boy breaks glass with voice

Standing waves  Caused by the interference of reflected waves with incident waves from the source.  Nodes: pts of no displacement  Antinodes: pts of maximum displacement Applet (try at home) Applet (try at home) Applet Wine glass harp Wine glass harp Wine glass harp Wine glass harp

Vibrating Columns of Air  Column will emit a sound when the air inside achieves resonance. DEMO (cardboard moose call) DEMO (cardboard moose call)  Frequency of vibration depend on Length of column Length of column Type of column Type of column Open endOpen end Closed endClosed end

Calculations for closed pipe FFFFundamental frequency f1= v /4L (L=length of air column) HHHHarmonics fn = nf1 (n=1,3,5,…) λ =4L/n NNNNote: only ODD harmonics are produced AAAA nnnn iiii mmmm aaaa tttt iiii oooo nnnn

Fundamentals and Harmonics  Fundamental Frequency: lowest frequency of vibration  Harmonics: whole number multiples of the fundamental Note: the fundamental frequency is the 1 st harmonic. Note: the fundamental frequency is the 1 st harmonic.  Animation Animation

Closed (at one end) pipe  The standing wave created has Node at closed-end Node at closed-end Antinode at open-end Antinode at open-end N A

Open pipe  The standing wave created has Antinode at both ends Antinode at both ends PVC pipe musicPVC pipe musicPVC pipe musicPVC pipe musicAA

Calculations for open pipe FFFFundamental frequency f1= v /2L (L=length of air column) HHHHarmonics fn = nf1 (n=1,2,3,…) λ =2L/n NNNNote: ALL harmonics are produced aaaa nnnn iiii mmmm aaaa tttt iiii oooo nnnn