Warm Up

Think back to our first day of this waves unit (Tuesday) when an object was dropped in the tub of water....

What do the waves you saw have in common with the waves of the electromagnetic spectrum?

What is a Wave?What is a Wave?

• Repeating disturbance or Repeating disturbance or movement that carries energy movement that carries energy through matter or spacethrough matter or space

Mechanical Waves vs. Mechanical Waves vs. Electromagnetic WavesElectromagnetic Waves

• Mechanical Waves-can only Mechanical Waves-can only travel through mattertravel through matter

• Sound wavesSound waves

• Earthquake wavesEarthquake waves

• Electromagnetic Waves- can Electromagnetic Waves- can travel through spacetravel through space

• Radio, micro, and gamma waves etc.Radio, micro, and gamma waves etc.

Two Basic Types of Waves Two Basic Types of Waves we Studywe Study

• Transverse WavesTransverse Waves– Ocean WavesOcean Waves– Radio WavesRadio Waves– Light WavesLight Waves– Heat WavesHeat Waves

• Longitudinal Longitudinal WavesWaves– Sound WavesSound Waves– Some Earthquake Some Earthquake

WavesWaves

Transverse WavesTransverse Waves

• Move in an up and down motion at Move in an up and down motion at a right angle to the direction of the a right angle to the direction of the wavewave

Parts of a Transverse Parts of a Transverse WaveWave

• CrestCrest: highest point of the wave: highest point of the wave• TroughTrough: lowest point of the wave: lowest point of the wave

Parts of a Transverse Parts of a Transverse Wave cont’dWave cont’d

Wavelength: () Distance between a point on

one wave to the identical point on the next wave

Amplitude: (a) Distance from the crest or trough

of a wave to the resting point

Longitudinal WaveLongitudinal Wave

• Matter vibrates in Matter vibrates in the direction of the the direction of the wavewave

• Examples: Sound Examples: Sound waves, springs, waves, springs, coilscoils

How does a Longitudinal wave How does a Longitudinal wave work?work?

• Compressions expand to an area that is Compressions expand to an area that is lessless dense dense

• RarefactionRarefaction: The less dense area in a : The less dense area in a compressional wavecompressional wave

How Does a Longitudinal Wave How Does a Longitudinal Wave Work? (Cont’d)Work? (Cont’d)

• Wavelength Wavelength ((): One compression and ): One compression and one rarefractionone rarefraction

Wave SpeedWave Speed

• Velocity of a wave is calculated by Velocity of a wave is calculated by multiplying wavelength by multiplying wavelength by frequencyfrequency

VVw w = = x f x f

*As f increases, decreases!

Frequency

Frequency – how many waves pass a point per unit of time.

We usually measure frequency in Hertz (number of waves per second)

What do you usually think of when you hear the term “Hertz”?

Period (T)

T=1/f

Period is the amount of time it takes for 1 wave to pass

Example Problem 1:Example Problem 1:

• A wave is generated in a wave pool at A wave is generated in a wave pool at an amusement park. The wavelength is an amusement park. The wavelength is 3.2 m and the frequency is 0.60 Hz. 3.2 m and the frequency is 0.60 Hz. What is the velocity of the wave?What is the velocity of the wave?

V = V = xx f f

1.92 m/s1.92 m/s

Example Problem 2:Example Problem 2:

• Earthquakes can produce three Earthquakes can produce three types of waves. One of these is a types of waves. One of these is a transverse wave called an “s” transverse wave called an “s” wave. A typical s wave travels at wave. A typical s wave travels at 5000 m/s. Its wavelength is 417 m. 5000 m/s. Its wavelength is 417 m. What is its frequency? What is its frequency?

•F = 12 HzF = 12 Hz

Example Problem 3:Example Problem 3:

• A sound wave has a frequency of A sound wave has a frequency of 500.0 Hz and a wavelength of 3.0 500.0 Hz and a wavelength of 3.0 m. What is the speed of the wave?m. What is the speed of the wave?

V = V = xx f f

Example Problem 4Example Problem 4

• The lowest-pitched sounds humans The lowest-pitched sounds humans can hear have a frequency of 20.0 can hear have a frequency of 20.0 Hz. What is the wavelength of Hz. What is the wavelength of these sound waves if their wave these sound waves if their wave speed is 340.0 m/s?speed is 340.0 m/s?

V = V = xx f f

Frequency and PitchFrequency and Pitch

• PitchPitch: The highness or lowness of : The highness or lowness of soundsound

• Depends on the frequencyDepends on the frequency• High frequency = high pitch High frequency = high pitch • Low frequency = low pitchLow frequency = low pitch

• 20,000 Hz: ultrasonic waves20,000 Hz: ultrasonic waves• 20 Hz and below: infrasonic 20 Hz and below: infrasonic waveswaves

Intensity and Intensity and LoudnessLoudness

• IntensityIntensity: Energy of the wave: Energy of the wave

• LoudnessLoudness: Human perception of : Human perception of sound intensity.sound intensity.– Depends on the Depends on the amplitudeamplitude

Decibel Scale (dB) - Measures intensity of Decibel Scale (dB) - Measures intensity of soundsound

How Loud? How Loud? How High or Low?How High or Low?

• Decibel Scale (dB) - Measures intensity Decibel Scale (dB) - Measures intensity of soundof sound

• Pitch – how high or low a sound seems Pitch – how high or low a sound seems to beto be– Depends on freqencyDepends on freqency– Higher f, higher the soundHigher f, higher the sound– Lower f, lower the soundLower f, lower the sound– Ave range humans – 440 Hz – 7000 HzAve range humans – 440 Hz – 7000 Hz

• Ultrasonic - >100,000 HzUltrasonic - >100,000 Hz• Infrasonic – subsonic - <20 HzInfrasonic – subsonic - <20 Hz

Doppler EffectDoppler Effecthttp://www.lon-capa.org/~mmp/applist/doppler/d.htm

Change in Change in frequency due to frequency due to a moving objecta moving object

• Sound moving Sound moving and the observer and the observer is stationaryis stationary