WAVESWAVESChapter 25Chapter 25

The Nature of WavesThe Nature of Waves

Ia. Ia. WaveWave:: a repeating disturbance or a repeating disturbance or movement that transfers movement that transfers energy through space or energy through space or mattermatter..

Ex light, sound, radioEx light, sound, radio

Ib. Ib. Medium:Medium:any material that a any material that a wave transfers energy wave transfers energy throughthrough

ex. Water is the mediumex. Water is the medium for ocean wavesfor ocean waves

II. II. 2 Types of Waves2 Types of Waves

1. Transverse

2. Longitudinal (Compressional)

1a. Transverse Waves1a. Transverse Waves

Particles of the medium vibrate perpendicular (up & down) to the direction the wave is moving.

Direction of Wave

Motion of Molecules

2a. Longitudinal Waves2a. Longitudinal Waves particles vibration is parallel to the

direction of the wave. These waves require a medium (such as air or water) through which to travel.

ex. Sound waves (looks like a spring)

Direction of Wave

Direction of Movement

III. Wave Properties- III. Wave Properties- DefinitionsDefinitions

a.a. WavelengthWavelength – the distance between one – the distance between one point on a wave and the nearest point point on a wave and the nearest point just like it. The greek symbol is just like it. The greek symbol is , , called called lambda.lambda.

b.b. FrequencyFrequency – number of wavelengths ( – number of wavelengths () ) that pass a given point each secondthat pass a given point each second

c.c. CrestCrest – the highest point of a transverse – the highest point of a transverse wavewave

Definitions continued….Definitions continued….

d.d. TroughTrough – the lowest point on a – the lowest point on a transverse wavetransverse wave

e.e. AmplitudeAmplitude – the measure of the energy – the measure of the energy of the wave (height for TW) of the wave (height for TW) ex. Large amplitude = more ex. Large amplitude = more energyenergy

f.f. Nodal LineNodal Line – an imaginary line, it is the – an imaginary line, it is the usual resting position of a waveusual resting position of a wave

Draw a transverse wave large enough to label 6 parts .

IV. Transverse Wave Diagrams

Parts of a Tranverse Wave

Crest is the top of the wave

Crest

Trough is the bottom of the wave

Trough

Wavelength

The wavelength is the distance from one crest of a wave to the

corresponding crest in the next wave or from one trough to the next trough.

Wavelength

Wavelength

Amplitude is the distance from the nodal line to the crest or the nodal

line to the trough.

Amplitude

V. V. Parts of a longitudinal Parts of a longitudinal wave are:wave are:

A.A. A A compressioncompression is the part where the is the part where the particles of matter are pushed close particles of matter are pushed close together.together.

B.B. A A rarefactionrarefaction is the part where particles of is the part where particles of matter are spread apart.matter are spread apart.

C.C. The The wavelengthwavelength is one complete is one complete compression and one complete rarefaction. compression and one complete rarefaction. SI unit is in meters. SI unit is in meters.

Parts of a Longitudinal WaveParts of a Longitudinal WaveCompression

the part where the particles of matter are pushed together

Longitudinal Wave DiagramsLongitudinal Wave DiagramsRarefaction

part where particles of matter are spread apart

Parts of a Longitudinal WaveParts of a Longitudinal WaveWavelength

Compression & Rarefactiontogether

compression rarefaction

Compressional Wave

VI. Calculating Wave SpeedVI. Calculating Wave Speed

Frequency Frequency is the number is the number of waves that pass a of waves that pass a given point each second. given point each second. The SI unit for frequency The SI unit for frequency is is HertzHertz (Hz)(Hz)..

At a constant speed, there At a constant speed, there is an inverse relationship is an inverse relationship between frequency and between frequency and wavelengthwavelength::

V = F V = F

V = Velocity of the wave (m/s) F = Frequency (hertz) (hz)

= wavelength (m)

is the Greek symbol called “lambda”.

Measuring Transverse WavesMeasuring Transverse Waves

Interactive WebsiteInteractive Website

V = F V = F Practice Practice ProblemsProblems

A. What is the velocity of a wave that has a frequency of 20hz and a wavelength of 3 m ?

GIVEN FORMULA SUB ANSWER & UNIT

V = = F

V = F V = F Practice Practice ProblemsProblems

A. What is the velocity of a wave that has a frequency of 20hz and a wavelength of 3 m ?GIVEN FORMULA SUB ANSWER & UNITV=V

F = 20hz

= 3m

V = = F

V = F V = F Practice Practice ProblemsProblems

A. What is the velocity of a wave that has a frequency of 20hz and a wavelength of 3 m ?

GIVEN FORMULA SUB ANSWER & UNIT

V=V

F = 20hz

= 3m

V = = F V = = 20 3

V = F V = F Practice Practice ProblemsProblems

A. What is the velocity of a wave that has a frequency of 20hz and a wavelength of 3 m ?

GIVEN FORMULA SUB ANSWER & UNIT

V=V

F = 20hz

= 3m

V = = F V = = 20 3

60 m/s

V = F V = F Practice Practice ProblemsProblems

B. What is the frequency of a wave traveling at 16 m/s with a wavelength of 8 m ?

GIVEN FORMULA SUB ANSWER & UNIT

V = = F

V = F V = F Practice Practice ProblemsProblems

B. What is the frequency of a wave traveling at 16 m/s with a wavelength of 8 m ?

GIVEN FORMULA SUB ANSWER & UNIT

V=16m/s

F = F

= 8m

V = = F

V = F V = F Practice Practice ProblemsProblems

B. What is the frequency of a wave traveling at 16 m/s with a wavelength of 8 m ?

GIVEN FORMULA SUB ANSWER & UNIT

V=16m/s

F = F

= 8m

V = = F 16 = = F 8

V = F V = F Practice Practice ProblemsProblems

B. What is the frequency of a wave traveling at 16 m/s with a wavelength of 8 m ?

GIVEN FORMULA SUB ANSWER & UNIT

V=16m/s

F = F

= 8m

V = = F 16 = = F 8 8 8

V = F V = F Practice Practice ProblemsProblems

B. What is the frequency of a wave traveling at 16 m/s with a wavelength of 8 m ?

GIVEN FORMULA SUB ANSWER & UNIT

V=16m/s

F = F

= 8m

V = = F 16 = = F 8 8 8

2 hz

C. What is the wavelength of a wave traveling at 9 m/s with a frequency of 36 hz ?

GIVEN FORMULA SUB ANSWER & UNIT

V = F V = F Practice Practice ProblemsProblems

C. What is the wavelength of a wave traveling at 9 m/s with a frequency of 36 hz ?

GIVEN FORMULA SUB ANSWER & UNIT

V=9m/s

F = 36hz

=

V = = F

V = F V = F Practice Practice ProblemsProblems

GIVEN FORMULA SUB ANSWER & UNIT

V=9m/s

F = 36hz

=

V = = F 9 = = 36

C. What is the wavelength of a wave traveling at 9 m/s with a frequency of 36 hz ?

V = F V = F Practice Practice ProblemsProblems

GIVEN FORMULA SUB ANSWER & UNIT

V=9m/s

F = 36hz

=

V = = F 9 = = 36 36 36

C. What is the wavelength of a wave traveling at 9 m/s with a frequency of 36 Hz ?

V = F V = F Practice Practice ProblemsProblems

GIVEN FORMULA SUB ANSWER & UNIT

V=9m/s

F = 36hz

=

V = = F 9 = = 36 36 36 1/4 or 0.25 m

C. What is the wavelength of a wave traveling at 9 m/s with a frequency of 36 Hz ?

VI. VI. ReflectionReflection is the is the bouncing back of bouncing back of a wavea wave

ex. Your reflection in a mirror

VII. VII. TheThe Law of Law of ReflectionReflection: :

all waves bounce off all waves bounce off of a surface at the of a surface at the same angle they same angle they

strike the surface. strike the surface. TheThee angle of e angle of

incidence is equal to incidence is equal to the angle of the angle of reflection.reflection.

Normal

VIII VIII RefractionRefraction: : the the bending of a wave bending of a wave caused by a change in speedcaused by a change in speed of the of the

wavewaveas it passes from onas it passes from one e medium to medium to another.another.

Ex. Objects look distorted under water

IX. DIFFRACTION:

The bendingof a wave as it passesan edge or opening

Ex. Ocean waves change direction and bend after striking an island

Diffraction of a Monochromatic Light SourceDiffraction of a Monochromatic Light Source

Ripple TankRipple Tank

XI. XI. InterferenceInterference

The combination of 2 or more The combination of 2 or more waves – 2 types:waves – 2 types:

a. Constructive Interferencea. Constructive Interference

b. Destructive Interferenceb. Destructive Interference

a. a. Constructive interferenceConstructive interference

occurs when waves occurs when waves align in sync – are align in sync – are added togetheradded together

Ex. in sound waves constructive Ex. in sound waves constructive interference causes a louder soundinterference causes a louder sound

b. b. Destructive interferenceDestructive interference

occurs when sound occurs when sound waves are out of sync. waves are out of sync. They subtract from They subtract from each other.each other.Ex. in sound waves destructive Ex. in sound waves destructive interference causes a softer soundinterference causes a softer sound

XII. XII. ResonanceResonanceis the ability of an is the ability of an object to vibrate by object to vibrate by absorbing energy at absorbing energy at its natural frequencyits natural frequency

Ex. A “singing” wine glassEx. A “singing” wine glass

http://www.howstuffworks.com/question603.http://www.howstuffworks.com/question603.htmhtmsinging wine glass” videosinging wine glass” video

Tacoma Bridge DisasterTacoma Bridge Disaster

Tacoma Washington BridgeTacoma Washington Bridge

Tacoma Bridge -- TwistTacoma Bridge -- TwistOne sidewalk was 28 feet higher than One sidewalk was 28 feet higher than the other.the other.

Tacoma Bridge -- TwistTacoma Bridge -- TwistOne sidewalk was 28 feet One sidewalk was 28 feet higher than the other.higher than the other.

Tacoma Bridge -- TwistTacoma Bridge -- Twist

Tacoma Bridge -- BreakTacoma Bridge -- Break

Bridge -- Side Span SagBridge -- Side Span Sag

Tacoma Bridge -- AfterTacoma Bridge -- After

Obj. 12. Another type of compressional Obj. 12. Another type of compressional wave is created by earthquakes. wave is created by earthquakes. Earthquakes occur along plate boundaries Earthquakes occur along plate boundaries in fault zones. As the plates move, stress in fault zones. As the plates move, stress becomes so great that the rocks break. becomes so great that the rocks break. When the rocks break, energy is released When the rocks break, energy is released in the form of seismic waves. The primary in the form of seismic waves. The primary (or P) waves are longitudinal.(or P) waves are longitudinal.

THE ENDTHE END