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DefinitionWave: Any transfer of energy

without a transfer of matter

Wave Pulse: the disturbance that transfers energy

Periodic Wave: a series of identical, repeating evenly spaced pulses

Medium: The substance through which waves pass or propagate

Transverse Wave: A wave in which a medium moves perpendicular to the direction of wave propagation

Longitudinal Wave: A wave in which a medium moves parallel to the direction of wave propagation

http://cnx.org/content/m12378/latest/Translong.swf

Vibrations & Waves

http://www.stmary.ws/highschool/physics/home/notes/waves/Intro_wave_phenomena.htm

Condensations: areas of maximum compressions; analogous to crests

Rarefactions: areas of maximum separation; analogous to troughs.

Vibrations & WavesWavelength - Distance between peaks Amplitude - Max Height above resting spot

Related to the energy carried by the waveCorresponds to loudness in sound waves

and brightness in light waves Frequency - Number of Bounces/secondPeriod - Time of a complete vibrationPeriod = 1 / Frequency T = 1/fFrequency = 1 / Period

Waves can be produced in two ways:a. Vibration of particles - this requires a medium for transfer

(mechanical wave)ex) sound, water wave, spring wave

b. Small changes in the strength of an electromagnetic field

- this requires no medium for transfer   ex) light, microwaves, x-rays

Pulses & Periodic Waves 1. Pulse – single vibratory disturbance that moves from point to

point  (Medium only moves up and down) 

Ex)In which direction will segment X move as the wave passes through it?

(1) down, only (2) up, only (3) down, then up, then down (4) up, then down, then up

Pulses & Periodic Waves 1. Pulse – single vibratory disturbance that moves from point to

point  (Medium only moves up and down) 

Ex)In which direction will segment X move as the wave passes through it?

(1) down, only (2) up, only (3) down, then up, then down (4) up, then down, then up

a.When the pulse (wave) reaches a boundary with another medium, part is reflected and part is transmitted (goes through)

From high speed to low speed (low density to high density)

From low speed to high speed (high density to low density)

Reflection from a rigid boundary(reflected wave undergoes a 180o phase change)

Reflection from a free boundaryreflected wave has the same polarity (no phase change) as the incident wave

b. When a pulse reaches a fixed, unyielding boundary, then the pulse is completely reflected and inverted (180°)

Wave characteristicshttp://www.stmary.ws/highschool/physics/ho

me/animations3/waves/Wave_Characteristics.html

http://www.stmary.ws/highschool/physics/home/animations3/waves/waves2.html

Frequency exampleEx) A wave generator operating for 4 seconds

produces the waves drawn below.Top view of a periodic wave (Each line is a crest)

How many waves are drawn between A and B? (Be careful!!)

8 cycles

exampleEx) A wave generator operating for 4 seconds

produces the waves drawn below.Top view of a periodic wave (Each line is a crest)

What is the frequency of this periodic wave train?

f = 8 cycles/4 sec = 2 cycles/sec = 2 Hz

FrequencyIn Sound, frequency is pitch.

-Human Ear: Frequency Range  20 Hz - 20,000 Hz.

http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter19/animation__effect_of_sound_waves_on_cochlear_structures__quiz_2_.html

 In Light, frequency is color.

Period T = 1/fPeriod (seconds) – time for an entire wave cycle to

pass a given point in a medium- determined by source of vibration not medium

Ex) The frequency of a light wave is 5.0 x 1014 hertz. What is the period of the wave?

T = 1/f   = 1/(5.0 x 1014 hertz)  = 2.0 x 10-15 s

B (will take the longest  to pass by)

Amplitude Amplitude – maximum change in position of a

particle from its rest position during a single vibration

- determined by source of vibration, not medium

Amplitude of a wave shows the amount of energy in the wave

Amplitude is a measure of loudness for sound and brightness for color -

"In Phase" (0°) – points on a single periodic wave that have the same displacement (from equilibrium  position) and moving in the same direction

Whole number of wavelengths apartA & E, A & I, A & MB & F, B & J, B & N

"Out of Phase"– (1800) - same displacement from equilibrium position but going in a different direction

½, 1½, 2½ etc wavelengths apartA & C, B & D, F & H

C and F

Name 2 points that are 180° out of phase?

B and D E and G

Wavelength λWavelength – distance between two consecutive

points in phasedetermined by medium λ = length of one cycle in meters / # of cycles

Ex) Wavelength?

λ = 5.0 m/2.5 cycles  λ = 2.0 m

Ex) Amplitude? Wavelength?

Amplitude = .10 mWavelength = .60 m

Ex) Amplitude A?, B?, C?

Amplitude of A = 2.0 mAmplitude of B = 2.0 mAmplitude of C = 1.0 m

Speed: v = f λSpeed – the number of meters a single cycle

travels per second

Speed of wave depends on the medium

(slower in dense media)

http://www.stmary.ws/highschool/physics/home/review/outsideContent/waves/speedMechanical_wave.htm

Speed: v = f λSpeed – the number of

meters a single cycle travels per second

Solve for f : f = v / λ

Frequency and

Wavelength are INVERSELY RELATED

Ex) f = 40. hertz. V = ?

(1) 13 m/s (2) 27 m/s(3) 60. m/s (4) 120 m/s

V = fλ 

V = 40. Hz(1.5 m)  (3) 60. m/s

Hw Pg 153-155 #1 - 47

VelocityVelocity sound = 3.3 x 102 m/s(Air, Reference Table, room temperature)

Velocity light in a vacuum = 3 x 108 m/s

About how many times faster is light than sound?

About 1 million times

Depends on the material of the vibrating medium

Sound can vibrate water, wood (speaker enclosures, pianos), metal, plastic, etc.

Sound speed in dry air is 330 meters/second at 0o C

Faster in warm air, slower in coldWater 4 times faster, steel 15 times faster

Source MediumFrequency Speed

Period Wavelength

Amplitude

Doppler Effecthttp:/0/science.discovery.com/videos/time-do

ppler-effect.htmlSheldon explains:

http://www.youtube.com/watch?v=Y5KaeCZ_AaY

http://www.stmary.ws/highschool/physics/home/animations3/waves/DopplerEffectTrain.html

Doppler EffectDoppler Effect – variation in the observed

frequency of a wave when there is relative motion between the source of the wave and the receiver

Because car is “driving into it’s sound wave” the observer in front of car hears a higher frequency.An observer behind the car hears a lower frequency.

To the right, wherethe frequency is higher

Doppler effect on electromagnetic wavesFor Electromagnetic waves, such as visible

light, the frequency change is recorded as a color shift.

Astrophysicist site this phenomenon as proof that universe is expanding.

Sonic BoomOr

- What happens when you go faster than the speed of sound

http://www.metacafe.com/watch/1956849/sonic_boom/

Interesting Fact:The crack of a whip is the sound of the

tip breaking the speed of sound.

Wave Front– locus of adjacent points on a wave which are in

phaseTop View

Superposition Superposition – when waves overlap, the

resultant displacement is the algebraic sum of the individual displacements of each wave – This causes interference

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Interference– effect produced by two waves passing

simultaneously through a region

There exist two kinds of interference:1.Constructive interference 2.Destructive interference

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As the two waves belowpass through eachother, the medium atpoint P will …

(1) vibrate up and down (2) vibrate left and right (3) vibrate into and out of the page(4) remain stationaryJune 2004

As the two waves belowpass through eachother, the medium atpoint P will …

(1) vibrate up and down (2) vibrate left and right (3) vibrate into and out of the page(4) remain stationaryJune 2004

What will the amplitude of the resultant wave be when wave A and B meet at point X?

Amp A + Amp B = 2 + -1 = +1

What is the amplitude of the wave producedwhen these waves overlap?

15 cm

Symmetrical Lines of Interferencehttp://www.stmary.ws/highschool/physics/ho

me/animations3/waves/interference.swfwave patterns produced by the overlap of 2

wave fronts in phaseMaximum Constructive Interference – Phase

difference – whole wavelengthMaximum Destructive Interference -

Phase Difference - 1/2 wavelengthhttp://techtv.mit.edu/tags/1750-interference/v

ideos/632-mit-physics-demo----microwave-interference

Destructive Interference

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multimedia/lesson44/lessonp.html

Standing Waveshttp://www.stmary.ws/highschool/physics/

home/animations3/standingWaves.swf

Standing Wave – waves produced when two waves of the same frequency and amplitude travel in opposite directions in the same medium (ex. Musical instruments)

http://video.google.com/videoplay?docid=5614877943718237184#docid=6482474251978139047

definitionsAntinode – The point of maximum

displacement of a medium

Node – Regions of zero displacement of the medium.

Caused by maximum destructive interference

Standing waves can also be created by reflection

How many Nodes?

5

How many antinodes?

4

How many waves?

2

http://www.physicsclassroom.com/Class/waves/U10L4e.cfm

Periodic Wave PhenomenaBeats and resonance

http://video.mit.edu/watch/tuning-forks-resonance-a-beat-frequency-11447/

BeatsOccur when two sound waves of nearly the same

frequencies (ex. 256Hz and 258 Hz) interact with one another

Beat Freq: Larger freq – smaller freqPitch of resulting soundwave is the average of the two

freq.

In our example f1 = 256 Hz f2 = 258 Hz

Beat Frequency : f2 - f1 = 258 Hz – 256 Hz = 2 beats / sec

Pitch = avg. freq = f2 + f1 = 258 Hz + 256 Hz = 257 Hz

2 2

When the forced vibration matches a natural frequency we get a “resonance” condition

Think about a swing on a playgroundYou go high when you pump the swing

at its natural vibration frequencySympathetic vibrations in tuning forksFamous Tacoma Narrows bridge

collapsehttp://videos.howstuffworks.com/tlc/29833-understanding-

tacoma-narrows-bridge-video.htm

ResonanceResonance – Building up of energy by

adding small amounts of energy in time with the natural frequency of an object

Resonance FrequencyResonance Frequency – natural

frequency that an object vibrates when disturbed

Can sound be used to break glass? Great video!

http://techtv.mit.edu/videos/2964-breaking-glass-with-sound

http://www.youtube.com/watch?v=BE827gwnnk4

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Diffraction – the spreading out of a wave into the region behind an obstacle

Amount of Diffraction depends on Wavelength & Size of Slit.

Diffraction increaseswhen size of the slit approaches  wavelength size.

http://www.stmary.ws/highschool/physics/home/notes/waves/WaveBehavior/diffractionSlitD.swf

hwPg 159 – 161 #48-71

When a sound wave reflects from a surface we generate an echo

Wave reflection from surfaces depends on the characteristics of the surface

Smooth hard surfaces reflect bestRough soft surfaces reflect poorlyEnergy not reflected is absorbed or

transmitted through the material

Think of arrows pointing in the direction of the wave motion

We can trace the path of these arrowsAngle of incidence = Angle of reflection

(θ1=θ2)

Angles Equal

Acoustics of room design is very interesting. Need some reflections to “liven” the room. Too many reflections and the sound gets mushy. Look in a concert hall or auditorium to see the different sound treatments

If there is a change in the characteristics of a medium, waves are bent

This occurs because different parts of the wave front travel at different speeds

Think of a marching around a curved track

The inside people have to move more slowly than the outside people to keep the lines straight

The combination of reflection and refraction enables imaging

Ultrasonic medical imagingNaval SONAR for detecting

submarinesBats catch mosquitoes