Waves

WavesA 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.

WavesWaves 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!!!)

Waves•Two types of waves

•Mechanical Waves•Need a medium to travel through•Ex. Sound, water

•Electromagnetic waves•Do not need a medium to travel through•Ex. Light, radio

Waves•Waves have two shapes

•Longitudinal•Transverse

WavesLongitudinal Waves (compression waves)

•Moves parallel to the wave motion•Sound waves are longitudinal waves

Parts of A Longitudinal Wave•Compression -compact area of wave•Rarefaction -less dense area of compression Wave

1Wavelength=1compression+1rarefraction

WavesTransverse Waves

•Moves perpendicular to the direction the wave moves

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

http://aplusphysics.com/courses/honors/waves/characteristics.html

http://hermes.ffn.ub.es/~albert/ones/wavemotion.html

http://www.youtube.com/watch?v=_ckjttBin58

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

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

Harmonic MotionPeriod

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

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

•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

WavesSpeed is frequency times wavelength

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

The wavelength for a wave is 0.5 meter, and its frequency is 40 hertz. What is the speed of this wave?

Waves in MotionIn 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.

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

Plane Waves And Circular Waves•Plane 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

Waves in Motion

Wave Interactions

• Wave interactions are when waves interact with an object or another wave

• Four types of interactions–Reflection–Refraction–Diffraction–Absorption

Reflection• Reflection – bouncing back of a wave

after it strikes a barrier

Angle of incidence = angle of reflection

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.

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

Waves in MotionAbsorption•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.

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

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

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)

http://www.aplusphysics.com/courses/regents/waves/regents_wave_interference.html

http://www.youtube.com/watch?v=YuveKkmeFWg

Doppler Effect

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

Resting Sound Source

sourceat rest

observer at rest

Frequency fs Frequency foV=340m/s

Sound source moving toward observer

source observer at rest

Frequency fs

Observer hears increased pitch(shorter wave length)

Sound source moving away from observer

sourceobserver at rest

Frequency fs

Observer hears decreased pitch(longer wave length)

BIG BANG THEORY

• http://www.youtube.com/watch?v=Tn35SB1_NYI

• http://www.youtube.com/watch?v=Kg9F5pN5tlI