2 Waves A wave is an oscillation that travels from one place to another. The word oscillation means a motion that repeats regularly.The surface of the water oscillates in response to the ball being poked and the oscillation spreads outward from where it started.An oscillation that travels is a wave.
3 WavesWaves carry information and energy and waves spread through connectionsThink of a stringRadio waves carry television signalsMicrowaves carry cellphoneconversations or facebook/twitter/instagram/ snapchat updates(aka WHAT REALLY MATTERS!!!)
4 Waves Two types of waves Mechanical Waves Electromagnetic waves Need a medium to travel throughEx. Sound, waterElectromagnetic wavesDo not need a medium to travel throughEx. Light, radio
6 Waves Longitudinal Waves (compression waves) Moves parallel to the wave motionSound waves are longitudinal waves
7 Parts of A Longitudinal Wave •Compression -compact area of wave•Rarefaction -less dense area of compression Wave1Wavelength=1compression+1rarefraction
8 Transverse Waves Moves perpendicular to the direction the wave moves
9 Parts of a transverse wave •Crest -highest point of wave•Trough -lowest point of wave•Wavelength -distance between one point in awave and the exact point on the next wave.•Amplitude -distance from crest or trough to middle
11 WavesWe use the Greek letter “lambda” to represent wavelength. A lambda (λ)looks like an upside down “y.”
12 Waves Frequency In an oscillator, frequency is the number of cycles it makes per secondThe unit of measurement is hertz (Hz)A frequency of one cycle per onesecond is one hertz
13 Harmonic Motion Period Is the length of time for one cycle; how long it takes for one repetition
14 Harmonic MotionFrequency and period are inversely related. The period is the time per cycle. The frequency is the number of cycles per time.
15 SpeedThe speed of a wave describes how fast the wave can transmit an oscillation one place to another.Waves can have a wide range of speeds:Most water waves are slow (1-2 mph)Sound waves move ~660 mphLight waves are extremely fast 186,000 miles per second
16 Waves Speed is frequency times wavelength In one complete cycle, a wave movesmoves forward one wavelength.
17 The wavelength for a wave is 0. 5 meter, and its frequency is 40 hertz The wavelength for a wave is 0.5 meter, and its frequency is 40 hertz. What is the speed of this wave?speed = 40 Hz × 0.5 m = 40 (1/sec) × 0.5 mspeed = 20 m/secThe speed of the wave is 20 m/sec.
18 Waves in Motion In what shapes do we find waves? What happens when a wave hits something?We will start with waves in water as they are easy to make and observe.Every process we see with water waves also occurs with sound and light waves.
19 In water waves, crests are also called wave fronts. Waves in MotionIn water waves, crests are also called wave fronts.
20 Plane Waves And Circular Waves The crest of a plane wave is a straight lineIt is started by disturbing the water in a lineIt moves perpendicular to the wave frontsCircular WavesCrests of circular waves are circlesThey are started by disturbing the waterat a single pointCircular waves radiate outward from thecenter
22 Wave Interactions Four types of interactions Reflection Refraction Wave interactions are when waves interact with an object or another waveFour types of interactionsReflectionRefractionDiffractionAbsorption
23 ReflectionReflection – bouncing back of a wave after it strikes a barrierAngle of incidence = angle of reflection
24 RefractionRefraction – bending of a wave as it moves from one medium to anotherMedium changes - wave passes from one medium to another (solid to gas, liquid to solid etc)The speed of the wave changes as it moves into mediumof different density and causes wave to bend)Speed is affected by density of the medium.
25 DiffractionDiffraction – The bending of a wave as a result of the interaction between a wave and the edge of an objectExamples:Waves bend around a rock in the oceanWaves bend around your legs when you stand in the surf at the beach and come together after they pass your legs
26 Waves in Motion Absorption When the amplitude of a wave gets smaller and smaller as it passes through a materialThe wave energy is transferred to theabsorbing material.
27 Amplitude changes, speed and frequency do not InterferenceInterference – effect of two or more waves intersectingwave-wave interaction or wave overlapIt’s what happens when waves meetAmplitude changes, speed and frequency do not
28 Constructive Interference resulting wave gets bigger – “additive”energy increaseshappens if both wave crests on the same side of the line of origintwo crests at the same location – amplitude of wave formed is the sum of the amplitudes
29 Destructive Interference Resulting wave gets smaller (subtract)Energy lossCrest of one wave meets trough of another wave2 possibilities: 1. single wave of reduced amplitude OR 2. no wave at allIf crest and troughs are equal but opposite – result is no wave at all (cancel each other out)