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Waves

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**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.

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Waves Waves carry information and energy and waves spread through connections Think of a string Radio waves carry television signals Microwaves carry cellphone conversations or facebook/twitter/instagram/ snapchat updates (aka WHAT REALLY MATTERS!!!)

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**Waves Two types of waves Mechanical Waves Electromagnetic waves**

Need a medium to travel through Ex. Sound, water Electromagnetic waves Do not need a medium to travel through Ex. Light, radio

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**Waves have two shapes Longitudinal Transverse**

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**Waves Longitudinal Waves (compression waves)**

Moves parallel to the wave motion Sound waves are longitudinal waves

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**Parts of A Longitudinal Wave**

•Compression -compact area of wave •Rarefaction -less dense area of compression Wave 1Wavelength=1compression+1rarefraction

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**Transverse Waves Moves perpendicular to the direction the wave moves**

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**Parts of a transverse wave**

•Crest -highest point of wave •Trough -lowest point of wave •Wavelength -distance between one point in a wave and the exact point on the next wave. •Amplitude -distance from crest or trough to middle

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Waves We use the Greek letter “lambda” to represent wavelength. A lambda (λ) looks like an upside down “y.”

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**Waves Frequency In an oscillator, frequency is the number**

of cycles it makes per second The unit of measurement is hertz (Hz) A frequency of one cycle per one second is one hertz

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**Harmonic Motion Period**

Is the length of time for one cycle; how long it takes for one repetition

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Harmonic Motion Frequency and period are inversely related. The period is the time per cycle. The frequency is the number of cycles per time.

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Speed The 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 mph Light waves are extremely fast 186,000 miles per second

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**Waves Speed is frequency times wavelength**

In one complete cycle, a wave moves moves forward one wavelength.

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**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 m speed = 20 m/sec The speed of the wave is 20 m/sec.

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**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.

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**In water waves, crests are also called wave fronts.**

Waves in Motion In water waves, crests are also called wave fronts.

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**Plane Waves And Circular Waves**

The crest of a plane wave is a straight line It is started by disturbing the water in a line It moves perpendicular to the wave fronts Circular Waves Crests of circular waves are circles They are started by disturbing the water at a single point Circular waves radiate outward from the center

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Waves in Motion

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**Wave Interactions Four types of interactions Reflection Refraction**

Wave interactions are when waves interact with an object or another wave Four types of interactions Reflection Refraction Diffraction Absorption

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Reflection Reflection – bouncing back of a wave after it strikes a barrier Angle of incidence = angle of reflection

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Refraction Refraction – bending of a wave as it moves from one medium to another Medium 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 medium of different density and causes wave to bend) Speed is affected by density of the medium.

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Diffraction Diffraction – The bending of a wave as a result of the interaction between a wave and the edge of an object Examples: Waves bend around a rock in the ocean Waves bend around your legs when you stand in the surf at the beach and come together after they pass your legs

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**Waves in Motion Absorption**

When the amplitude of a wave gets smaller and smaller as it passes through a material The wave energy is transferred to the absorbing material.

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**Amplitude changes, speed and frequency do not**

Interference Interference – effect of two or more waves intersecting wave-wave interaction or wave overlap It’s what happens when waves meet Amplitude changes, speed and frequency do not

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**Constructive Interference**

resulting wave gets bigger – “additive” energy increases happens if both wave crests on the same side of the line of origin two crests at the same location – amplitude of wave formed is the sum of the amplitudes

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**Destructive Interference**

Resulting wave gets smaller (subtract) Energy loss Crest of one wave meets trough of another wave 2 possibilities: 1. single wave of reduced amplitude OR 2. no wave at all If crest and troughs are equal but opposite – result is no wave at all (cancel each other out)

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**http://www. aplusphysics**

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Doppler Effect Doppler effect is the change in frequency of a wave for an observer moving relative to its source.

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**Resting Sound Source Frequency fs V=340m/s Frequency fo source at rest**

observer at rest

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**Sound source moving toward observer**

Observer hears increased pitch (shorter wave length) Frequency fs source observer at rest

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**Sound source moving away from observer**

Observer hears decreased pitch (longer wave length) Frequency fs observer at rest source

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BIG BANG THEORY

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