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Wave. a disturbance that propagates through a material medium or space . Waves transfer energy without the bulk transport of matter. Mechanical Wave. In order for a mechanical wave to exist, energy is needed to create a disturbance in an elastic medium .
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Wave a disturbance that propagates through a material medium or space. Waves transfer energy without the bulk transport of matter.
Mechanical Wave In order for a mechanical wave to exist, energy is needed to create a disturbance in an elastic medium.
No medium is needed for ELECTROMAGNETICwaves. Light, radio, x-rays, and gamma rays are some examples of e/m waves. All e/m wavestravel through free space at a speed of approximately 3.00 x 108 m/s or 186,000 miles/sec. This speed is known as thespeed of light.
TRANSVERSE The displacement of the particles of the medium isperpendicularto the direction of wave propagation.
LONGITUDINAL The displacement of the particles of the mediumisparallelto the direction of wave propagation.
SURFACE A combination of transverse and longitudinal.
A seagull floating on the ocean moves up and down as waves pass.
Amplitude the maximum displacement of a particle of the medium from the rest or equilibrium position denoted by A and measured in units of length
Wavelength the shortest distance between two points that are “in phase” denoted by l and measured in units of length
Frequency- the number of complete vibrations per unit time denoted by f and measured in units of Hz
Velocity - the speed of the wave denoted by v and measured in units of dist/time The speed of a wave depends on the properties of the medium through which it is traveling. v = d/t = l/T = fl
Period - the shortest time interval during which the motion of the wave repeats itself denoted by T and measured in units of time T = 1/f & f = 1/T
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.
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.
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.
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.
Reflection the turning back of a wave when it reaches the boundary of the medium through which it is traveling
Law of Reflection the angle of incidence is equal to the angle of reflection
There are two types of reflection. Fixed-end Termination the reflected wave is inverted when it reflects from a more dense medium
There are two types of reflection. Free-end Termination the reflected wave is upright when it reflects from a less dense medium
Refraction thebendingof a wave as it passesobliquelyfrom one medium into another of different propagation speed For refraction to occur, the wave must change speed and must enter the new medium at an oblique angle.
Diffraction thespreadingof a wave around a barrier or through an opening
Interference the result of the superposition of two or more waves Superposition Principle the displacement of the medium when two or more waves pass through it at the same time is the algebraic sum of the displacements caused by the individual waves
Types of Interference Constructive results in a larger amplitude Destructive results in a smaller amplitude
“Mini Seismic” Waves Though 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 a beetle 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.
When two plates slide past each other, they create a transform fault, like the San Andreas fault.
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.
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.
What types of forcesare created? Tension Force: • stretching or pulling force • Makes a normal fault
Normal Fault http://www.geo.uib.no/jordskjelv/index.php?topic=earthquakes&lang=en
What types of forces are created? Compression Force: • force pushing something together • Makes a reverse fault
Reverse Fault http://www.geo.uib.no/jordskjelv/index.php?topic=earthquakes&lang=en
What types of forces are created? Shear Force: • a system of forces that operates against a body from different sides • Makes a strike-slip fault
Strike-Slip Fault http://www.geo.uib.no/jordskjelv/index.php?topic=earthquakes&lang=en
Seismic Waves Seismic 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.
Tsunami! What happened & why
2004 Indian Ocean Earthquake • Undersea earthquake • Magnitude 9.0 (Moment magnitude scale) NOAA
Epicenter 150 KM west of Sumatra http://en.wikipedia.org/wiki/2004_Indian_Ocean_earthquake
Occurred along the subduction zone where the Indian dives under the Eurasian Plate http://www.nps.gov/prsf/geology/images/plates.gif
