conceptual physics 1 sound & music 13-sep-15 physics 1 (garcia) sjsu origin of sound sound is a...

Conceptual Physics 1

Sound & Music

Apr 19, 2023 Physics 1 (Garcia) SJSU

Origin of Sound

Sound is a wave that is produced by the vibrations of material objects.

Tuning fork

Guitar stringDrumhead

Conceptual Physics Chapter 26 3

The Origin of Sound

• All sound waves are produced by the vibration of a material object. E.g., the reed of a saxophone, the string of a guitar or the tines of a tuning fork.

• Sound waves are longitudinal waves that transport acoustic energy through a medium by particle-to-particle interactions between neighboring molecules as they oscillate back and forth.

• The frequency of the sound wave produced is equal to the frequency of the vibrating source.


The Origin of Sound

• The transmission of sound requires a medium. There may be vibrations, but if there is nothing to compress and expand, there can be no sound.

• Sound waves can propagate through solids, liquids and gases, but can not travel through a vacuum.


The Origin of Sound

• Sound can be heard from the ringing bell when air is inside the jar, but not when the air is removed.


Sound in Air

Consider sound waves in a tube.• When the prong of a tuning fork next to the tube moves

toward the tube, a compression enters the tube. • When the prong swings away, in the opposite direction,

a rarefaction follows the compression. • As the source vibrates, a series of compressions and

rarefactions is produced.


The Decibel Scale

• Since the range of intensities that can be detected by the human ear is very large, a logarithmic scale, based on powers of ten, is used to measure intensity levels. This intensity level is measured in decibels (dB).

• A 50 dB sound is 100 times more intense than a 30 dB sound and 1000 times more intense than a 20 dB sound.

Nature of Sound in Air

Sound in air is a longitudinal wave created by compressions and rarefactions.


Demo: Sound is not Wind

With sound, air molecules oscillate in place.

With wind, air moves from place to place.

Smoke rings are not sound because the air moves from place to place.


Demo: Light & Sound

Sound waves can only travel through a material, such as air, water, etc.

Light and radio waves can travel through vacuum.

See the cell phone ringing inside vacuum chamber but don’t hear any sound.

Radio

Wav

e


Check Yourself

Do light waves have energy?

What do we call the type of heat transfer that occurs when light transfers energy?

Do sound waves have also have energy?


Media That Transmit Sound

Sound travels better through elastic liquids and solids, such as water and rocks, than through air.

This is due to the close proximity of the atoms as they vibrate.

Hear richer, louder sound transmitted by string


What Your Voice Sounds Like

Your voice sounds different to you when you hear it from a recording.

This is because when you are speaking aloud, most sound waves reach your ear traveling through the solid flesh and bone of your skull. Leave yourself

a voice-mail

Human Ear

Pressure variations of sound waves push the eardrum, whose vibrations are transmitted by the ossicles (ear bones) to the cochlea (hearing canal)

CochleaVibrations transmitted by the ear bones create oscillations

in the fluid with the cochlea (snail in Latin), which is a spiral-wrapped tube.

These oscillations within the cochlea cause the basilar membrane to ripple, like a waving flag.

Organ of Corti

The organ of Corti forms a ribbon of sensory epithelium that runs lengthwise down the entire cochlea.

The hair cells of the organ of Corti selectively transform the oscillations of the basilar membrane into nerve signals.


Loudness & Amplitude

Loudness depends on amplitude of pressure and density variations in sound waves.

DecibelsLoudness of sound depends on the amplitude of pressure variations in the sound waves.

Loudness is measured in decibels (dB), which is a logarithmic scale (since our perception of loudness varies logarithmically).

From the threshold of hearing (0 dB) to the threshold of pain (120 dB) the pressure increase is a million times higher.

At the threshold of pain (120 db) the pressure variation is only about 10 Pascals, which is one ten thousandths atmospheric pressure.


Demo: Make Some Noise

Let’s experience the loudness of sound like by clapping at various decibel levels.

SoundMeter

Start clapping softly and slowly increase or decrease loudness, as I direct you using the sound meter.

Hearing by Age & Sex

Hearing acuity decreases with age, especially in the high frequencies.In general, women have greater acoustic sensitivity than men.

Absolute thresholds of hearing by age in males and females

Male, Age 20

Male, Age 30

Male, Age 40

Male, Age 50

Male, Age 60

Female, Age 60

Hearing Loss

Hair cells that respond to high frequency sound are very vulnerable to destruction, and loss of these neurons typically produces difficulty understanding human voices.

Much of this type of permanent hearing loss is avoidable by reducing exposure, such as to loud music.

The hair cells that line the cochlea are a delicate and vulnerable part of the ear. Repeated or sustained exposure to loud noise destroys the neurons of the Organ of Corti.

Once destroyed, the hair cells are not replaced, and the sound frequencies interpreted by them are no longer heard.

What?


Speed of Sound in Air

Speed of sound in air is about 340 m/s.

Sound travels about one kilometer in three seconds, about one mile in five seconds.

Light is a million times faster than sound.


Demo: Helium Voice

Sound speed in helium is higher than speed in air.

Wavelength of sound unchanged (size of vocal cords is unchanged).

Frequency of voice is higher since

He

Talk like me!

(Wave speed)(Wavelength)(Frequency) =

Breath Helium…


Reflection of Sound

Sound reflects strongly from rigid surfaces.

Softer surfaces absorb sound.

Quiet after a fresh snowfall because the soft, irregular surface of the snow absorbs sound instead of reflecting it.


Check Yourself

When crowded, which restaurant will be quieter?


Singing in the Shower

Multiple reflections from the hard walls create reverberation.

Hear your voice from several sources, slightly shifted in time.

Reverberation extends each note and smears (smoothens) the pitch.

Your voice sounds better when singing in the shower


Refraction of Sound

Sound speed can vary by material or conditions.

This causes the sound to bend in direction, in the same way that light bends when it passes through a glass lens.

Fig. 20.8


Ultrasound

Ultrasound is high frequency (Megahertz), short wavelength

(0.1 mm) sound.

Reflections and refractions of ultrasound by flesh and bone allow “seeing” inside the human body.


Forced Vibrations

Vibrating guitar strings force the vibration of the guitar’s body, producing most of the sound.

553 Hz 731 Hz

Circular rings indicate where the surface is vibrating up and down


Demo: Tuning Fork & Sound Box

Tuning fork by itself is not very loud.

Sound is much louder if it is held against a sound box, such as the body of a guitar or any similar rigid surface.

The tuning fork forces the surface into oscillation at the same frequency.


Natural Frequency

Metal wrench and wooden bat sound very different when dropped to the floor.

Different materials and shapes vibrate at their own natural frequencies.


Demo: Singing Rod

Stoking an aluminum rod with rosin-covered fingers induces loud vibrations at the rod’s natural frequency.


ResonanceResonance occurs when forced vibrations match an

object’s natural frequency.

Oscillations grow in amplitude due to synchronized transfer of energy into the vibrating object.

Acoustic Resonance

Sound at an object’s natural frequency can produce resonant vibrations.

If the amplitude of the sound is sufficiently large, resonant vibrations can shatter a wine glass.

As shown by Myth Busters, this may even be achieved by exceptionally powerful singers (and by average singers using electronic amplifiers).


Beats

• When two sound waves differing slightly in frequency are superimposed they will not maintain a constant phase relationship.

• This leads to alternating reinforcement and cancellation of the sound energy.

• The audible result is a series of pulsations called beats.

400 & 401 Hz sounds – 1 beat per second400 & 403 Hz sounds – 3 beats per second400 & 410 Hz sounds – 10 beats per second


Beats

• The pattern of alternating constructive and destructive interference can be found from applying the law of superposition to the interfering waves.


Beats

• Beats can occur with any kind of wave and are a practical way to compare frequencies.

• To tune a piano, a piano tuner listens for beats produced between a standard tuning fork and a particular string on the piano.

• When the frequencies are identical, the beats disappear. • The members of an orchestra tune up by listening for

beats between their instruments and a standard tone.


Tacoma Narrows Bridge

In 1940, the first Tacoma Narrows bridge was destroyed by resonance.

First Bridge

Second Bridge


Movie: Tacoma Narrows Bridge

Chapter 21Musical Sounds

Noise Versus Music• What is the difference between noise

and music?– Answer: The appearance of the waveform.

Mic&Osc

Pitch...• … is the "highness" or "lowness" of a

tone.

• Pitch corresponds to frequency.

• Concert A on the Musical Scale has a frequency of 440 Hertz.

Sound Intensity and Loudness

• Intensity of Sound– refers to the amplitude of the pressure

variations in the sound wave

Loudness• the physiological sensation directly

related to the sound intensity

• measured in bels (1bels = 10 decibels)

= 10 log(I/Io)

Demo – Sound Meter

Source of Sound Loudness (db)

Threshold of Hearing 0

Conversation 60

Ear Damage Begins 85

Amplified Music 110

Jet Airplane at 30 meters 140

Common Sound Intensities

Source of Sound Intensity, I (W/m2)Sound Level, (db)

Threshold of Hearing I0 = 10-12 0

10

20

40

60

70

90

110

120

140

10-11

10-10

10-8

10-6

10-5

10-3

10-1

1

102

Rustle of Leaves

Whisper

Quiet Radio in Home

Conversation in Home

Busy Street Traffic

Riveter

Disco Music Amplified

Air-raid Siren, Nearby

Jet, 30 m Away

• Loudness– Increase the loudness by 10db and you

increase the intensity by 10.– Increase the loudness by 20db and you

increase the intensity by 100.

• Increase the loudness by 30db an you increase the intensity by ...

A. 10

B. 100

C. 200

D. 1000

E. 10000

Quality...• …is the characteristic sound that

allows us to distinguish between two musical instruments. (a.k.a. timbre)

• Partial Tones - one of the many frequencies present in a complex tone

• Demo: Guitar String Tones

• Fundamental Frequency– the lowest frequency of vibration– a.k.a. the first harmonic

• Harmonic– a partial tone that is an integer multiple

of the fundamental frequency

Fourier Analysis...

• …is a mathematical method that will resolve any periodic wave form into a series of simple sine waves.

• See Figure 21.9.

BackBack

Open Organ PipeModes of Vibration

• Open Organ Pipe Table– Harmonics– Wavelength– Frequency– Nodes & Antinodes– e.g. Spinning Tubes

Closed Organ PipeModes of Vibration

• Closed Organ Pipe Table– Harmonics– Wavelength– Frequency– Nodes & Antinodes– e.g Ruben’s Tube and Coke Bottles

1. _________ is the bending in the direction a wave travels due to the fact that the medium is not uniform.

a. refraction

b. diffraction

c. reflection

d. absorption

2. A vibrating tuning fork causes an identical fork to vibrate. This is called ___________.

a. refraction

b. resonance

c. beats

d. reverberation

3. A grandfather clock runs too slow. Which of the following could you do to correct this?

a. remove some mass from the bob

b. increase the amplitude

c. move the bob down

d. move the bob up

4. The lowest frequency that can be produced on a guitar string has a wavelength ________ as long as the string.

a. twice

b. half

c. four times

d. one fourth

5. A decibel is a measure of a sound’s

a. frequency

b. wavelength

c. speed

d. loudness

e. all of these

6. A violin and a piano sound different because they play sounds of different ____________.

a. amplitude b. quality

c. frequency d. wavelength

7. The natural frequency of a whistle is 1020 Hz. If you observe its frequency to be 1010 Hz, you can conclude

a. you and the source are moving farther away from each other

b. the source is moving c. you and the source are both movingd. the source and you are moving closer togethere. more that 40 m/s

8. Two waves having the same amplitude and frequency interfere as a crest meets a trough. The result will be _____.

a. constructive interference

b. destructive interference

c. resonance

d. standing waves

9. If you observe the beat frequency between two speakers to be ten hertz and if you know one of the speakers is 250 hertz, what are the other possible frequencies for the second speaker?

a. 240 and 260 hertz

b. 230 and 270 hertz

c. 250 and 240 hertz

d. 200 and 300 hertz

10. The longitudinal waves produced on a slinky more closely represent which of the following waves?

a. water waves

b. light waves

c. sound waves

d. transverse waves on a guitar string

conceptual physics 1 sound & music 13-sep-15 physics 1 (garcia) sjsu origin of sound sound is a...

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