WAVE MOTION

WAVES A vibration that repeats regularly in

space and time Transmitted from one place to another

w/out actually transporting matter A transmission of Energy Require a medium (substance to travel

through)

Ex. Water waves, sound, wave in string/spring

KANAGAWA OKI NAMI URA - “THE GREAT WAVE OFF OF KANAGUA” - BY HOKUSAI

DESCRIBING A WAVE

Wavelength – (λ) – distance between identical parts of a wave. Length of wave

Amplitude (A)– height of a wave Period (T) - time for one full wave to

pass Frequency (f) – cycles per second … how

many full waves pass by per second

FREQUENCY & PERIOD Frequency = 1/ Period

Period = 1 / Frequency

Reciprocals of each other….Waves per time (frequency)Time per wave (Period)

SIMPLE HARMONIC MOTION Any regularly repeating vibration

PendulumSpringVibrations caused in buildings by windSteps of a person walking

Rules for waves can be used for anything that fits in this category

WAVE MOTION Transfers energy not matter If stone dropped in water, the disturbance

moves not the water

WAVE SPEED Wave speed depends on the medium The more rigid the medium the faster

sound will travel through it Wave speed = frequency X wavelength

v = f λ

TRANSVERSE WAVES

Medium vibrates in a directions perpendicular to the direction of the wave

LONGITUDINAL WAVES Medium vibrates in the same direction

that the wave moves

INTERFERENCE Constructive Interference

Waves can interfere w/ each other so that they add together to produce a larger wave

Destructive Interference Waves can interfere w/ each other so

that they subtract each other and cancel out

Demos

• Out of phase– Destructive interference

• In phase– Constructive interference

DIFFRACTION When waves collide w/ a barrier they have

a tendency to wrap around the barrier Break walls at the beach This is why we can hear a person talking

even if they are around the corner

DIFFRACTION

ENERGY OF WAVES- TSUNAMIS Tsunamis are large waves generated by

a large earthquake or massive landslide Travel at hundreds of miles per hour,

have low amplitudes out at sea, but can become very high when approaching shore

http://www.funkybiology.com/Destructive_Force_of_Tsunami_Waves_mov.mov

http://www.youtube.com/watch?v=dJBS94GVyuo

http://www.youtube.com/watch?v=BAuWa77vYDU

http://www.youtube.com/watch?v=z-t5qe_VSEA

http://www.youtube.com/watch?v=wHtvA-lIksU

http://www.youtube.com/watch?v=sBkMLYUyUZg&safe=active (new)

SOUND Longitudinal wave Sound travels as a region of compressed

air The areas in between compressed

regions are called “rarefactions” Speed of sound is about 340 m/s in air Like any wave the speed depends on

the medium

SOUND Frequency of a sound wave affects the

“pitch” or how we hear a sound Higher frequency, higher the pitch Humans can typically hear pitches

ranging from 20 Hz (infrasonic) to 20,000 Hz (ultrasonic), but that range diminishes as you age… typically at the high end

Loudness of a sound is affected only by amplitude

http://www.cbu.edu/~jvarrian/applets/doppler1/doppler.htm

http://www.youtube.com/watch?v=AXhRmv1mrs4&safe=active Hearing test

http://en.wikipedia.org/wiki/52-Hertz_whale lonely whale

http://www.youtube.com/watch?v=h5l4Rt4Ol7M&safe=active Hearing test

DOPPLER EFFECT Waves From an object that is

approaching have short wavelength, which means they have a higher freq. And a higher pitch

waves coming from an object that is moving away from you have a longer wavelength and therefore a lower freq, and lower pitch

Cars approaching and leaving

BOW SHOCK/SONIC BOOM Sometimes the source of a wave can

travel faster than the waves it is creating

http://www.youtube.com/watch?v=6o0zmafxTmE&safe=active

Can be easily seen with a speed boat http://

www.youtube.com/watch?v=2Sv4o4Kktm4&safe=active

Sonic boom created when a object or plane breaks through the sound barrier

Standing waves• Stationary wave caused by interference between a wave and its reflection

– Two waves of equal amplitude and wavelength pass through each other in opposite directions.

• Nodes – stationary points– Where waves our “out of phase” --- crest lined up with trough

• Antinodes- points of largest amplitude– Where waves are “in phase” - crest lined up with crest

• Standing Wave in Water• Standing wave demo• Standing waves created by speaker• Swimming pool• When an object is forced into vibrating at one of its natural frequencies, it vibrates in a manner

such that a standing wave is formed within the object.

Tacoma Narrows Bridge

• http://www.youtube.com/watch?v=3mclp9QmCGs

Resonance• When an object vibrates at its natural

frequency, a dramatic increase in amplitude occurs

• Resonance happens when a standing wave is created

• Break Glass w/ voice? • Mythbusters

Beats• Two tones of slightly different frequency are

sounded together. This produces a fluctuation in the loudness of combined sounds. – adfs

• Amount of beats per second is equal to the difference in frequencies. – Two tuning forks…. One 340 Hz another 310 Hz are

sounded together. Beats will occur at a frequency of 30 Hz