Warm-Up: March 27thWarm-Up: March 27th

1.1. What are the two types of mechanical What are the two types of mechanical waves?waves?

2.2. Sound is what kind of wave? Sound is what kind of wave?

3.3. What is the topmost part of a transverse What is the topmost part of a transverse wave called? wave called?

4.4. What makes up the wavelength of a What makes up the wavelength of a longitudinal wave (what two parts)? longitudinal wave (what two parts)?

5.5. If you can see the light coming from If you can see the light coming from another room (not directly), the lightwaves another room (not directly), the lightwaves are bending. What do we call that?are bending. What do we call that?

Sound WavesSound Waves

Longitudinal Longitudinal –– Disturbance of Disturbance of

medium is parallel medium is parallel to wave to wave movementmovement

MUST have a MUST have a medium to travel medium to travel inin

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!

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

Warmup March 28Warmup March 28thth Happy Happy Spring Break!!Spring Break!!

1.1. What kind of waves are sound What kind of waves are sound waves?waves?

A.A.LongitudinalLongitudinalB.B.ElectricalElectricalC.C.TransverseTransverseD.D.Both A and BBoth A and B

2. As frequency of a wave Increases, 2. As frequency of a wave Increases, the length of a wave ___________(if the length of a wave ___________(if velocity is same)velocity is same)

A.A.IncreasesIncreasesB.B.Stays the SameStays the SameC.C.DecreasesDecreases

3. Sound travels fastest through 3. Sound travels fastest through A.A. SolidSolidB.B. LiquidLiquidC.C. GasGas

4. Frequency of a wave determines a 4. Frequency of a wave determines a sound’s sound’s A.A. AmplitudeAmplitudeB.B. PitchPitchC.C. IntensityIntensity

5. What is the Frequency of a sound 5. What is the Frequency of a sound wave traveling 330m/s (in the air) wave traveling 330m/s (in the air) with a wavelength of .55 meters?with a wavelength of .55 meters?A.A. 1550 Hz1550 HzB.B. 800 Hz800 HzC.C. 775 Hz775 HzD.D. 600 Hz600 Hz

ANSWERS TO ANSWERS TO WARMUPWARMUP

1.A1.A

2.C2.C

3.A3.A

4.B4.B

5.D5.D

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

• LoudnessLoudness: Human perception of : Human perception of sound intensity.sound intensity.• Depends on the amplitudeDepends on the amplitude

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

Waves go through mediums, and different mediums are transparent to different types of wave energy.

But also, a wave’s energy can be partly or completely absorbed by the different medium

When Waves Hit ThingsWhen Waves Hit Things

Sound – as WavesSound – as Waves

Amplitude Amplitude = volume= volume

FrequencyFrequency = pitch. High frequency, high = pitch. High frequency, high pitch. Low frequency, low pitch. pitch. Low frequency, low pitch.

Must have a medium – no medium, no Must have a medium – no medium, no sound. sound.

Sound waves – What type of medium do Sound waves – What type of medium do they travel fastest through (solid, liquid, they travel fastest through (solid, liquid, gas)? gas)?

Measuring Sound

Decibel – a measure of the Sound Pressure Level. The higher the decibel, the more intense the sound.

Whisper Quiet Library at 6' 30dB

Normal conversation at 3' 60-65dB

City Traffic (inside car) 85dB

Level at which sustained exposure may result in hearing loss

90 - 95dB

Power mower at 3' 107dB

Listening to music with headphones

105-120 dB (earbuds add 6-9 dB)

Pain begins 125dB

12 Gauge Shotgun Blast 165dB

Death of hearing tissue 180dB

Loudest sound possible 194dB

It happened to my uncle…he was It happened to my uncle…he was one of the first people I ever knew one of the first people I ever knew

to own a to own a “SONY WALKMAN”“SONY WALKMAN”

He listened at very high volumes He listened at very high volumes pretty much all day…now he is pretty much all day…now he is

pretty much deaf……and it’s very pretty much deaf……and it’s very much annoying for us and him! much annoying for us and him!

DID YOU HEAR WHAT I SAID???DID YOU HEAR WHAT I SAID???

DON’T LET THIS HAPPEN TO DON’T LET THIS HAPPEN TO YOU!!!!!!!!YOU!!!!!!!!

August 27, 1883

Krakatoa

180 dB

Loudest sound ever heard.

The sound itself caused tsunamis

The Doppler EffectThe Doppler EffectThe What?????The What?????

Where have you heard the term Where have you heard the term “doppler” before?“doppler” before?

http://www.youtube.com/watch?v=h4OnBYrbCjY&authuser=0

http://www.youtube.com/watch?v=Djz_rtnXSfY&authuser=0

The Doppler EffectThe Doppler Effect

A change in the A change in the observedobserved frequency of a frequency of a wave when the source and observer (you) wave when the source and observer (you) are in motion relative to each other. are in motion relative to each other.

The frequency The frequency appearsappears to increase as the to increase as the source get closer, and appears to decrease source get closer, and appears to decrease as it moves away.as it moves away.

Cool sound stuff…

Supersonic (faster than the speed of sound)

Subsonic (slower than the speed of sound)

Sonic boom (what happens when you pass the speed of sound)

Infrasound (below 20 Hz)

Sound Waves Carry Energy!!

https://www.youtube.com/watch?v=BE827gwnnk4

Calculate the Wavelength of 3 Calculate the Wavelength of 3 different tuning forksdifferent tuning forks

Speed of sound in air is 330m/sSpeed of sound in air is 330m/s

The frequency of each fork is printed on The frequency of each fork is printed on the stemthe stem

Calculate the wavelength of three different Calculate the wavelength of three different tuning forks.tuning forks.

256, 312, 680256, 312, 680

VVw w = = x f x f