Waves Waves

Chapter 11 Section 1Chapter 11 Section 1

What is a What is a wavewave??

A A wavewave is a is a repeating disturbance repeating disturbance or movement that transfers or movement that transfers energyenergy through matter or space through matter or space

Waves transfer Waves transfer energyenergy NOT NOT mattermatter

MediumMedium: : the matter through which a the matter through which a wave travelswave travels; ; i.e. water, airi.e. water, air

Motion of a Duck on a WaveMotion of a Duck on a Wave

Water WaveWater Wave

Mechanical WavesMechanical Waves

Waves that can travel only through Waves that can travel only through mattermatter

There are There are two typestwo types::Transverse wavesTransverse waves (water, and (water, and

some seismic waves)some seismic waves)Longitudinal wavesLongitudinal waves (sound, spring)(sound, spring)

Requires a medium!!!!!!!Requires a medium!!!!!!!

Longitudinal (compressional) WavesLongitudinal (compressional) WavesParticles in the medium move parallel to Particles in the medium move parallel to

the direction of the waves.the direction of the waves.

particle motion

wave motion

The dense areas are called compressions.The less dense areas are rarefactions.

Transverse WavesTransverse WavesParticles in the medium move perpendicular to the Particles in the medium move perpendicular to the

direction of the waves. direction of the waves.

particlemotion

wave motion

Parts of a WaveParts of a WaveCrest:Crest: the highest point (top) of a the highest point (top) of a

transverse wave.transverse wave.Trough:Trough: the lowest point (bottom)the lowest point (bottom) of a of a

transverse wave. transverse wave.Wavelength:Wavelength: the distance from any point the distance from any point

on a wave to the same point on the next on a wave to the same point on the next wavewave. . (ex: crest to crest)(ex: crest to crest)

Amplitude:Amplitude: the height measured from the the height measured from the resting position.resting position.

trough

amplitude

crest

Parts of a WaveParts of a Wave

wavelength

Seismic WavesSeismic Waves

Seismic wavesSeismic waves are a are a combination of combination of compressional and transverse wavescompressional and transverse waves

1. They can travel along the earth’s 1. They can travel along the earth’s surfacesurface

2.2. When objects on the Earth’s surface When objects on the Earth’s surface absorb some of the energy carried by absorb some of the energy carried by seismic waves, they move and shakeseismic waves, they move and shake

Compressional

Transverse

AMPLITUDEAMPLITUDEMeasures the amount ofMeasures the amount of

energyenergy in a wave in a wave. .

Greater amplitude = Greater amplitude = more energymore energy..

FREQUENCYFREQUENCYThe rate at which waves pass The rate at which waves pass (the (the

# of full wavelengths that pass a # of full wavelengths that pass a point in one second).point in one second).

Symbol: Symbol: ff

Unit: Unit: Hertz (Hz)Hertz (Hz)

1 Hertz = 1 Hertz = 1 vibration per second1 vibration per second

Frequency is Frequency is 1 / T1 / T

WAVE SPEEDWAVE SPEEDHow fast a wave moves. How fast a wave moves.

Symbol: Symbol: vv Unit: Unit: m/sm/s

Wave speed is determined by the Wave speed is determined by the mediummedium.. Generally, waves pass Generally, waves pass through through solidssolids faster b/c particles faster b/c particles are closer and can pass vibrations are closer and can pass vibrations to each other more quickly.to each other more quickly.

Wave speed = frequency times wavelengthWave speed = frequency times wavelength

v = f v = f ·· λλ f = v / f = v / λλ

λλ = v / f = v / f

UNITS: UNITS: λλ = meters (m) = meters (m)

f = Hertz (Hz)f = Hertz (Hz)

v = m/sv = m/s

EQUATIONSEQUATIONS

v

f λ

The string of a piano that produces the note The string of a piano that produces the note middle C vibrates with a frequency of 264 Hz. middle C vibrates with a frequency of 264 Hz. If the sound waves produces have a If the sound waves produces have a wavelength of 1.30 m in air, what is the wavelength of 1.30 m in air, what is the speed of sound in air?speed of sound in air?f = 264 Hzf = 264 Hz

λλ = 1.30 m = 1.30 m

v = ?v = ?

v = 264 Hz (1.30 m)v = 264 Hz (1.30 m)

v = f · λ

v = 343.2 m/s

A water wave has a speed of 1.3 m/s. A A water wave has a speed of 1.3 m/s. A person sitting on a pier observes that it takes person sitting on a pier observes that it takes 1.2 s for a full wavelength to pass the edge of 1.2 s for a full wavelength to pass the edge of the pier. What is the wavelength of the water the pier. What is the wavelength of the water wave?wave?v = 1.3 m/sv = 1.3 m/sT = 1.2 sT = 1.2 sf f = 1 / T = 1 / 1.2 s = 1 / T = 1 / 1.2 s

= 0.83 Hz= 0.83 Hzλλ = ? = ?

λλ = 1.3 m/s / 0.83 Hz = 1.3 m/s / 0.83 Hz

λ = v / f

λ = 1.57 m