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a a disturbance disturbance that propagatesthat propagatesthrough a material through a material mediummedium or or spacespace..

Waves Waves transfer energytransfer energy withoutwithout

the bulk transport of the bulk transport of matter.matter.

Wave

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Mechanical WaveIn order for a In order for a mechanical wavemechanical wave to to exist, exist, energyenergy is needed to create is needed to create

a a disturbancedisturbance in an in an elastic elastic mediummedium..

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All e/m wavesAll e/m waves travel through freetravel through freespace at a speed of approximatelyspace at a speed of approximately

3.00 x 103.00 x 1088 m/s m/s oror 186,000 miles/sec 186,000 miles/sec..

This speed is known as theThis speed is known as the speed of lightspeed of light..

Light, radio, x-rays, and gamma raysLight, radio, x-rays, and gamma raysare some examples of e/m waves. are some examples of e/m waves.

No medium is needed forNo medium is needed forELECTROMAGNETICELECTROMAGNETIC waves.waves.

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The displacement of the particlesThe displacement of the particlesof the medium isof the medium is perpendicularperpendicular totothe direction of wave propagation.the direction of wave propagation.

TRANSVERSE

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LONGITUDINALThe displacement of the particlesThe displacement of the particlesof the mediumof the medium isis parallelparallel to theto thedirection of wave propagation.direction of wave propagation.

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SURFACEA A combinationcombination of of

transverse transverse and and longitudinallongitudinal..

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A seagull floating on the ocean moves up and down as waves pass.

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AmplitudeAmplitudethe the maximum displacementmaximum displacement

of a particle of the medium fromof a particle of the medium fromthe rest or equilibrium positionthe rest or equilibrium positiondenoted by A and measured in units of lengthdenoted by A and measured in units of length

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WavelengthWavelengththe the shortest distanceshortest distance

betweenbetweentwo points that are “in two points that are “in

phase”phase”denoted by denoted by and measured in units of length and measured in units of length

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FrequencyFrequency - - the number of complete the number of complete vibrations per unit timevibrations per unit time

denoted by f and measured in units of Hzdenoted by f and measured in units of Hz

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VelocityVelocity - the - the speedspeed of the wave of the wavedenoted by v and measured in units of dist/timedenoted by v and measured in units of dist/time

v = d/t = /T = f

The speed of a wave depends on the propertiesThe speed of a wave depends on the propertiesof the medium through which it is traveling.of the medium through which it is traveling.

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PeriodPeriod - - the shortest the shortest timetime interval during interval duringwhich the motion of the wave repeats itselfwhich the motion of the wave repeats itself

denoted by T and measured in units of timedenoted by T and measured in units of time

T = 1/f & f = 1/T

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Ever wondered how we got to the point of being able to measure time accurately using clocks?

• Galileo got the idea while sitting in church.

• He was fascinated by the swinging movements of the chandeliers hanging high overhead from the cathedral’s ceiling.

• Galileo noticed that, although the angle of the swinging movements changed over time, the amount of time required for the pendulum to swing in one direction and then return to its original starting point (known as the period of a pendulum) appeared to remain constant.

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Vibration of a Pendulum

• A pendulum’s swing is like a wave. Both repeat motion in cycles.

• The period of the pendulum depends only on the length of the pendulum and the acceleration of gravity.

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Vibration of a Pendulum

• In the same way that a long pendulum has a greater period, a person with long legs tends to walk with a slower stride than a person with short legs.

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Vibration of a Pendulum

The back-and-forth vibratory motion of a swinging pendulum is

called SIMPLE HARMONIC MOTION

***The source of all waves is something that vibrates.18

Reflectionthe the turning backturning back of a wave when of a wave whenit reaches the it reaches the boundaryboundary of the of the

medium through which it is travelingmedium through which it is traveling

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Law of Reflectionthe the angle of incidenceangle of incidence is is equalequal

to the to the angle of reflectionangle of reflection

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There are two types of reflection.Fixed-end TerminationFixed-end Terminationthe reflected wave is

inverted when it reflectsfrom a more dense medium

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There are two types of reflection.Free-end TerminationFree-end Terminationthe reflected wave is

upright when it reflectsfrom a less dense medium

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the bendingbending of a wave as it passes obliquelyobliquely from

one medium into another of different propagation different propagation

speedspeed

RefractioRefractionn

For refraction to occur, the waveFor refraction to occur, the wavemust change speed and must entermust change speed and must enterthe new medium at an oblique angle.the new medium at an oblique angle.

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DiffractionDiffractionthethe spreadingspreading of a of a

wavewavearound a barrier oraround a barrier orthrough an openingthrough an opening

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Interferencethe result of the the result of the superpositionsuperposition

of two or more wavesof two or more waves

Superposition Principlethe displacement of the medium whenthe displacement of the medium when

two or more waves pass throughtwo or more waves pass throughit at the same time is the it at the same time is the algebraicalgebraicsumsum of the displacements caused of the displacements caused

by the individual wavesby the individual waves25

ConstructiveConstructiveresults in a larger amplitudelarger amplitude

Types of InterferenceTypes of Interference

DestructiveDestructiveresults in a smaller amplitudesmaller amplitude

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Types of InterferenceTypes of Interference

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“Mini Seismic” WavesThough we might not refer to them as

seismic, anything moving on the ground can transmit waves through the ground. If you stand near a moving locomotive or a heard of charging elephants, you would feel these vibrations. Even something as small as abeetle generates pulses when it moves. These pulses can be detected by a nocturnal sand scorpion. Sensors on its eight legs can detect both longitudinal and surface waves. The scorpion can determine the direction of the waves based on which legs feel the waves first. It can determine the distance of the prey based on the time delay between the fast moving longitudinal waves and the slower moving surface waves. The greater the time delay, the farther away the beetle. This is the same way seismologists determine the distance of a quake’s epicenter. Sand is not the best conductor of waves, so the scorpion will only be able to detect beetles within about a half meter. 28

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When two plates slide past each other, they create a transform fault, like the San Andreas fault.

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• Earthquakes can happen in any of these situations. Despite the powerful forces driving plate movement, the plates themselves spend much of the time locked in place by the friction of the plates rubbing against each other. Eventually, however, they build up so much

pressure that the plates abruptly snap forward. Then the ground can shift a few feet—or a few dozen! Shock waves from that sudden motion shoot out in all directions, creating an earthquake. 31

Because the San Andreas fault curves around Los Angeles, and then again into the Pacific in northern California, the two plates cannot slide smoothly against each other. Instead, the complex stresses of plate movement have fractured the land and created dozens of smaller fault lines.

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Tension ForceTension Force: stretching or pulling force Makes a normal normal fault

What types of forcesWhat types of forces are created?

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http://www.geo.uib.no/jordskjelv/index.php?topic=earthquakes&lang=en 34

Compression ForceCompression Force: force pushingpushing something togethertogether Makes a reversereverse fault

What types of What types of forcesforces are created?

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http://www.geo.uib.no/jordskjelv/index.php?topic=earthquakes&lang=en 36

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Shear ForceShear Force: a system of forces that

operates against a body from different sides

Makes a strike-slipstrike-slip fault

What types of What types of forcesforces are created?

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http://www.geo.uib.no/jordskjelv/index.php?topic=earthquakes&lang=en 39

Seismic WavesSeismic waves use Earth itself as their medium. Earthquakes produce them and so does a nation when it carries out an underground nuclear test. (Other countries can detect them.) Seismic waves can be longitudinal, transverse, or surface waves. P and S type waves are called body waves, since they are not confined to the surface. Rayleigh waves do most of the shaking during a quake.

Name Type Info

P Wave Longitudinal Also known as primary, compressional, or acoustic waves; fastest seismic wave

S wave Transverse Also known as secondary, or shear waves; do not travel through fluids;

Rayleigh Wave

Surface Rolls along surface like a water wave; large amplitude

Love Wave Surface Ground moves side to side as wave moves forward 40

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Tsunami!Tsunami!What happened &

why

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2004 Indian Ocean Earthquake 2004 Indian Ocean Earthquake

NOAA

•Undersea earthquake•Magnitude 9.0 (Moment magnitude scale)

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http://en.wikipedia.org/wiki/2004_Indian_Ocean_earthquake

Epicenter 150 KM west of Epicenter 150 KM west of SumatraSumatra

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Occurred along the Occurred along the subduction zone where the subduction zone where the

Indian dives under the Indian dives under the Eurasian PlateEurasian Plate

http://www.nps.gov/prsf/geology/images/plates.gif 45

http://msnbc.msn.com/id/6770108/ 46

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http://home.cfl.rr.com/battleshipron/before_after.gif

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