physics 101: lecture 22, pg 1 physics sound review review and assessment with clickers! chapeter...

Physics 101: Lecture 22, Pg 1

Physics Sound ReviewPhysics Sound Review Review and Assessment with Clickers!

Chapeter test


Speed of SoundSpeed of Sound

sound waves require a medium to travel speed of those waves depends on the density

and atomic forces (tension) in the medium:

Speed = square root(Force /density)

Speed in air is given by V= 331 + 0.6*Temp



Rank these medium from fast to slow:

a. Air > water > steel

b. Steel > water > air

c. Water >air > steel

d. Trick question- all the same!


Speed of SoundSpeed of Sound Rank these from medium

from fast to slow

a. Air > water > steel

b. Steel > water > air

c. Water >air > steel

d. Trick question- all the same!

Medium Speed (m/s)

Steel 5600

Water 1500

Air 344

Steel is 15x air

Water is 3x air



speed in air is given by V= 330 + 0.6*Temp(where temp is always measured in celcius)

What is the speed of sound in m/s at room temperature which is about 20 C?

a. 340 b. 550

c. 343 d. 350


What is a Wave?What is a Wave? Movement (wiggle & jiggle) in Space & Time Transfer Energy (Info) without transferring Mass

All waves have similar properties! Sound vibrations move along with the wave

and are called longitudinal waves Light vibrations move perpendicular to the

wave’s motion and are called transverse


Transverse WavesTransverse WavesThe following video demonstrates the

motion of a Transverse Wave…


Longitudinal WavesLongitudinal WavesThe following video

demonstrates the motion of a Longitudinal Wave…


What type of wave is this?What type of wave is this?A. sound b. lightA. sound b. light

c. water wave d. radioc. water wave d. radio


What type of wave is this?What type of wave is this?A. A. sound sound b. light b. light

c. water wave d. radioc. water wave d. radio


Which statement is totally Which statement is totally true?true?

a.. sound is a longitudinal wave that does not exist at ultra sound frequencies

b. Sound is a transverse wave that exists at infrasonic and ultrasonic frequencies

c. Sound is a longitudinal wave that does not exist in outer space

d. Sound is a transverse wave that does not exist above 120 dB


Wave parts (M=10Wave parts (M=1066, , =10=10-6-6))

Crests

Troughs

Amplitude (A)

Wavelength (

Equilibrium

wavewave


Wave CharacteristicsWave Characteristics

v = f

Wavelength (: Distance it takes for Wave to repeat itself (units in meters)

Period (T): Time for one complete cycle (units in seconds)

Frequency (f): Number of complete cycles per unit time (units in 1/sec or Hz)

Unit Analysis: m/s = (m)(1/s)

f = 1/T

Wave Velocity (v): Speed of wave propagation (units in m/s)


What is shown What is shown here?here?

A. frequencyA. frequency b. wavelength b. wavelength

c. period c. period d. amplituded. amplitude


What is shown What is shown here?here?

A. frequencyA. frequency b. wavelengthb. wavelength

c. period c. period d. amplituded. amplitude


A 100 Hz wave contains 10 waves A 100 Hz wave contains 10 waves every 20 m. What is it’s speed?every 20 m. What is it’s speed?

A. 1 m/sA. 1 m/s b. 2 m/sb. 2 m/sc. 5m/sc. 5m/s d. 200 m/sd. 200 m/s

v = d/t v= f v = /T


If you shake a slinky at If you shake a slinky at twice the frequency…twice the frequency…

a. amplitude doublesa. amplitude doubles b. period doubles b. period doublesc. speed doublesc. speed doubles d. no answer d. no answer


Physics of MusicPhysics of Music

BeatBeat is humming sound between 2 is humming sound between 2 closely matched frequenciesclosely matched frequencies

(beat frequency= f(beat frequency= f22 – f – f11))

Octave Octave = double or half frequency= double or half frequency

half stephalf step = frequency * 1.059 = frequency * 1.059 (1.059 * itself 12 times = 2(1.059 * itself 12 times = 2

since 12 notes in an octave)since 12 notes in an octave)


Beats are due to interferenceBeats are due to interference

Consider two harmonic waves A and B meeting at x=0.

A(1t)

B(2t)

CONSTRUCTIVEINTERFERENCE

DESTRUCTIVEINTERFERENCE

C(t) = A(t) + B(t)


A4 is middle A on a piano with a 440Hz. A4 is middle A on a piano with a 440Hz. What is the frequency of the next A What is the frequency of the next A

note 12 keys higher?note 12 keys higher?A. 441A. 441 b. 880b. 880C. 439C. 439 d. 220d. 220


Your guitar string should play 256 Hz, Your guitar string should play 256 Hz, but when you play a 256Hz tuned but when you play a 256Hz tuned

piano key at the same time you hear a piano key at the same time you hear a beat frequency of 2 hz. What is the beat frequency of 2 hz. What is the

frequency of your strings?frequency of your strings?

A.A.2 2

b. 258b. 258

c. 254 or c. 254 or 258258

d. 512d. 512


Intensity and LoudnessIntensity and Loudness Intensity is the power per unit area. (W/m2)

I = P / A where P = power in watts

A = area = 4*pi *d2 (d=distance away)

Threshold for hearing I0 = 10-12 W/m2

Loudness (Decibels) is the perception of intensityMeasured on log scale using decibels = (10 dB) log10 ( I / I0)


Bow WavesBow Waves source of a wave moves

faster than the sound waves

Ex: Boat faster water waves

V-Shaped pattern of bow waves behind the boat.


Shock WavesShock Waves

A Shock Wave = 3-D version of 2-D Bow Wave.

Except that the shock wave is shaped conically while the bow wave is a V-Shape.


Sonic BoomSonic BoomPlane travels faster than soundSound waves overlap– constructive interferencesonic boom is continuously formed behind jet Mach number = speed plane / speed of sound

Mach = jet distance/sound distance

jet distance

Sound distance


Sonic BoomSonic BoomWhat is the mach number of this plane?

1. 1 2. 2 3. 3 4. 4


Sonic BoomSonic BoomWhat is the mach number of this plane?


Intensity and LoudnessIntensity and LoudnessRules of 10 dB

10 times more people is 10x more sound

it’s 10 more dB

it’s 10x more intense

but it only sounds 2x louder to us

Compare to 1 person whispering: 0 dB , Io

10 people talking: 10 dB, I = 10x, loudness = 2x

100 people talking: 20 dB, I=100x, loudness=4x

1000 people talking: 30 dB, I=1000x, loudness=8x


Intensity and LoudnessIntensity and LoudnessRules of 3 dB

2 times more people is 2x more intensity

but it only sounds 1.7x louder to us

Compare to 1 person whispering: 0 dB , Io

2 people talking: 3 dB, I = 2x,

4 people talking: 6 dB, I= 4x,

8 people talking: 9dB, I= 8x

16 people talking: 12 dB, I= 16x


Intensity ACTIntensity ACT Recall Intensity = P/A. If you are standing 6 meters

from a speaker, and you walk towards it until you are 3 meters away, by what factor has the intensity of the sound increased?

1) 2 2) 4 3) 8 4) 18


Decibels ACTDecibels ACT

If 1 person can shout with loudness 50 dB. How loud will it be when 100 people shout?

1) 52 dB 2) 70 dB 3) 150 dB


Intense Concert PhysicsIntense Concert PhysicsSuppose at a concert you want to quadruple (4x) how loud it sounds.

Since you can’t quadruple the number of speakers w/o permission,how much closer should you get to quadruple your listening pleasure?

1. 2x close 2. 4x closer 3. 8x closer 4. 16x closer


Intense Concert PhysicsIntense Concert PhysicsSuppose at a concert you want to decrease how loud it sounds

By 100 times using ear plugs. How many decibels is this?

1. 0dB 2. 3 dB 3. 6 dB 4. 20 dB


Intense Concert PhysicsIntense Concert PhysicsSuppose at a concert you want to decrease how loud it sounds

By 100 times using ear plugs. How many decibels is this?

1. 0dB 2. 3 dB 3. 10 dB 4. 20 dB


Constructive Constructive InterferenceInterference

Constructive Interference occurs when 2 waves combine with their troughs lining up, and their crests lining up.

Once aligned, a wave “grows” between the waves, demonstrating increased size.


Destructive Destructive Interference DiagramInterference Diagram

The following demonstrates Destructive Interference…


Standing Waves areStanding Waves areinteger multiples of harmonicsinteger multiples of harmonics

Node…. NodeStrings, flutes

/2, , 3/2 /, …

Anti-Node…. Nodeclarinet, palm pipe

/4, 3, 5/4 , …


How many waves is this How many waves is this 11stst harmonic harmonic

(fundamental)?(fundamental)?A. ¼ b. ½ c. 3/2 d. 1A. ¼ b. ½ c. 3/2 d. 1


Which harmonic wave is Which harmonic wave is this:this:

a. 1a. 1stst b. 2 b. 2ndnd c. 3 c. 3rdrd d. 4th d. 4th


This 3This 3rdrd harmonic forms in harmonic forms ina. guitara. guitar b. flute b. flute

c. clarinet d. organ pipec. clarinet d. organ pipe


Resonance ACTResonance ACT

What happens to the fundamental frequency of a pipe, if the air (v=300 m/s) is replaced by helium (v=900 m/s)?

1) Increases 2) Same 3) Decreases


Organ PipeOrgan Pipe

A 0.9 m organ pipe (open at both ends) is measured to have it’s first harmonic at a frequency of 382 Hz. What is the wavelength of this note?a. 1.8 m b. 0.9m c. 0.45m d. No idea and can’t draw

pictures

L=0.9 m



A 0.9 m organ pipe (open at both ends) is measured to have it’s first harmonic at a frequency of 382 Hz. What is the wavelength of this note?a. 1.8 m b. 0.9m c. 0.45m d. No idea and can’t draw

pictures

L=0.9 m



A 0.9 m organ pipe (open at both ends) has a speed of sound of 180 m/s. What is it’s frequency?

L=0.9 m

A.1.8 b. 180 c.100 d. Idk, need wavelength


DopplerDoppler Effect Effect When source is moving toward you:

Distance between waves decreasesFrequency increasesVelocity of sound is still same (same medium)

When source is moving away from you:Distance between waves increasesFrequency decreasesVelocity of sound is same (same air,same temp)


Preflight 5Preflight 5 As a police car passes you with its siren

on, the frequency of the sound you hear from its siren

1) Increases 2) Decreases 3) Same

Doppler Example Audio

Doppler Example Visual


Doppler ACTDoppler ACTA: You are driving along the highway at 65 mph, and behind you a police car, also traveling at 65 mph, has its siren turned on.

B: You have both pulled over to the side of the road, and a police car turns on a siren and travels past you as they chase after someone else

In which case does the frequency of the siren seem higher to you?

1. Case A 2. Case B 3. both 4. neither

vs

f

vo

f’v


SummarySummarySound travels as fast as the medium allows

it’s measured by wavelength and frequency

Two sounds close but not perfect make beats

You hear a higher or lower pitch when sound moves closer or further away

Resonance is the resounding of natural frequencies or harmonics creating timbre


That’s all folks!That’s all folks!

physics 101: lecture 22, pg 1 physics sound review review and assessment with clickers! chapeter...

Documents

speed of sound speed

water wave

sound waves

transverse wave slide

longitudinal wave slide

sound frequencies

sound vibrations

transverse slide