WavesWavesChapters 11, 12, 13Chapters 11, 12, 13

CH 11-1 The Nature of WavesCH 11-1 The Nature of Waves

wavewave: repeating disturbance or movement : repeating disturbance or movement that transfers energy through matter or that transfers energy through matter or spacespace

Figure 2 page 327Figure 2 page 327 All waves are produced by vibrations.All waves are produced by vibrations.

Mechanical WavesMechanical Waves

mediummedium: the matter the waves travel : the matter the waves travel throughthrough

The medium can be solid, liquid, gas, or a The medium can be solid, liquid, gas, or a combination of these.combination of these.

What is the medium for sound waves? What is the medium for sound waves? airair

What is the medium for ocean waves?What is the medium for ocean waves? waterwater

As a wave travels through a medium, As a wave travels through a medium, particles of the medium particles of the medium do notdo not travel with travel with the wave.the wave.

So, what do waves carry?So, what do waves carry?

Two Types of Mechanical WavesTwo Types of Mechanical Waves

1.1. transverse waves: transverse waves: matter in the medium moves back and matter in the medium moves back and forth at right angles to the direction the forth at right angles to the direction the wave travelswave travels

2.2. compressional (longitudinal) waves: compressional (longitudinal) waves: matter in the mediummatter in the mediummoves back and forth moves back and forth in the same direction in the same direction that the wave travelsthat the wave travels

Transverse WavesTransverse Waves

Compressional WavesCompressional Waves

The arrows represent motion of particles The arrows represent motion of particles of a medium and the motion of a wave of a medium and the motion of a wave traveling through the medium. Which traveling through the medium. Which combination best represents transverse combination best represents transverse waves?waves?

A. A. B.B.

C. C. D. D.

Three Types of WavesThree Types of Waves

Sound wavesSound waves compressional wavecompressional wave When a sound wave reaches your ear, it When a sound wave reaches your ear, it

causes your eardrum to vibrate. Your inner causes your eardrum to vibrate. Your inner ear then sends signals to your brain and your ear then sends signals to your brain and your brain interprets the signals as sound.brain interprets the signals as sound.

Three Types of WavesThree Types of Waves

Water wavesWater waves transverse (but not purely)transverse (but not purely) Ocean waves are caused by wind blowing Ocean waves are caused by wind blowing

across the water. The changing wind speed across the water. The changing wind speed acts like a vibration.acts like a vibration.

Three Types of WavesThree Types of Waves

Seismic wavesSeismic waves combination of compressional and transversecombination of compressional and transverse

CH 11-2—Wave PropertiesCH 11-2—Wave Properties Parts of a transverse waveParts of a transverse wave

crestcrest: highest point on a transverse wave: highest point on a transverse wave troughtrough: lowest point on a transverse wave: lowest point on a transverse wave

Parts of a compressional waveParts of a compressional wave compressioncompression: crowded regions of a : crowded regions of a

longitudinal wavelongitudinal wave rarefactionrarefaction: spread out regions of a : spread out regions of a

longitudinal wavelongitudinal wave

Properties of a WaveProperties of a Wave

wavelengthwavelength: distance between one point : distance between one point on a wave and the nearest point just like iton a wave and the nearest point just like it crest to crest, trough to trough (transverse)crest to crest, trough to trough (transverse) compression to compression, rarefaction to compression to compression, rarefaction to

rarefaction (longitudinal)rarefaction (longitudinal)

frequencyfrequency: number of wavelengths that : number of wavelengths that pass a fixed point each secondpass a fixed point each second

Finding frequency:Finding frequency: transverse wave—count # of crests or troughs transverse wave—count # of crests or troughs

that pass by a point each secondthat pass by a point each second compressional wave—count # of compressional wave—count # of

compressions or rarefactions that pass by a compressions or rarefactions that pass by a point each secondpoint each second

SI unit for frequency: Hertz (Hz)SI unit for frequency: Hertz (Hz)

Frequency and wavelength are related. Frequency and wavelength are related. As frequency increases, wavelength As frequency increases, wavelength decreases.decreases.

Calculating Wave SpeedCalculating Wave Speed

velocity = wavelength x frequencyvelocity = wavelength x frequency v = v = λλ x f x f

A wave is traveling at a speed of 18 m/s A wave is traveling at a speed of 18 m/s with a frequency of 3 Hz. A second wave is with a frequency of 3 Hz. A second wave is traveling at a speed of 16 m/s with a traveling at a speed of 16 m/s with a frequency of 4 Hz. What is the difference frequency of 4 Hz. What is the difference in the two wavelengths?in the two wavelengths? 2 m2 m

amplitudeamplitude: maximum distance the : maximum distance the particles of a medium are disturbed from particles of a medium are disturbed from their resting positions their resting positions transverse: distance from the crest or trough transverse: distance from the crest or trough

of the wave to the rest position of the mediumof the wave to the rest position of the medium compressional: related to how tightly the compressional: related to how tightly the

medium is pushed together at the medium is pushed together at the compressionscompressions

The greater amplitude—the more energy The greater amplitude—the more energy carried by the wave.carried by the wave.

CH 11-3 The Behavior of WavesCH 11-3 The Behavior of WavesReflectionReflection

Reflection occurs when a wave strikes an Reflection occurs when a wave strikes an object and bounces off of it.object and bounces off of it.

All types of waves, including sound, water, All types of waves, including sound, water, and light waves, can be reflected.and light waves, can be reflected.

RefractionRefraction A wave’s speed depends on the medium it A wave’s speed depends on the medium it

is moving through.is moving through. Refraction is the bending of a wave Refraction is the bending of a wave

caused by a change in its speed as it caused by a change in its speed as it moves from one medium to another.moves from one medium to another.

The greater the change in speed, the more The greater the change in speed, the more the wave bends.the wave bends.

DiffractionDiffraction Diffraction occurs when an object causes Diffraction occurs when an object causes

a wave to change direction and bend a wave to change direction and bend around it.around it.

Waves can also be diffracted when they Waves can also be diffracted when they pass through a narrow opening.pass through a narrow opening.

InterferenceInterference Interference occurs Interference occurs

when two or more when two or more waves overlap and waves overlap and combine to form a combine to form a new wave.new wave.

This new wave exists This new wave exists only while the original only while the original waves continue to waves continue to overlap.overlap.

ResonanceResonance

The ability of an object to vibrate by The ability of an object to vibrate by absorbing energy at its natural frequency absorbing energy at its natural frequency is called resonance.is called resonance.