Ch. 12 Honors Physics: Sound

The Fundamental Frequency

-Corresponds to nodes occurring only at the ends. The string vibrating up and down as a whole corresponds to a half wave length -The wavelength of the fundamental on the string is equal to twice the length of the string; therefore, L=1/2 x wavelength

What is a forced vibration? What is a natural frequency? How do these concepts relate to resonance?

-Forced vibration is when an alternate force is applied to a system. -Natural frequency is the frequency at which a system tends to oscillate without any outside force. -Resonance is connected because something forces an object to vibrate at its natural frequency.

What is a fundamental frequency? What are harmonics? What is the relationship between the two?

-Fundamental frequency is the lowest frequency of a wave and the 1st harmonic. -Harmonics are multiples of the fundamental frequency -Fundamental frequency = 1st harmonic of wave

What is the relationship between pitch and frequency?

-The frequency determines the pitch -We hear pitch, but it is truly the frequency of the sound wave

How do we measure volume?

-decibels -compressed scale, so the change in decibels is difficult due to the amount of sound and power needed

Doppler Radar

-shift in frequency based on motion -when source is closer, frequency is higher -when source is farther, the frequency is lower

Intensity

-the energy transported by a wave per unit time across a unit area perpendicular to the energy flow -is proportional to the square of amplitude - (W/m^2)

What does "out of phase" mean?

-waves crest and trough at different times -waves are 180 degrees out of phase when the waves are reflected over the x-axis

The decibel level at the threshold of human hearing is __________________.

0 dB

0 dB does not mean what?

0 intensity

Intensity base 0 equals...

1 x 10^-12 (threshold)

The human ear can detect sounds with an intensity as low as ______________________ and as high as ___________________.

1 x 10^-12 W/m^2 ; 1 W/m^2 (an even higher, although above this is painful)

1st Harmonic is ________ a wavelength. (open)

1/2

1st Harmonic is __________ a wavelength. (closed)

1/4

Each ______ dB corresponds to a __________-fold change in intensity.

10 ; 10 Example: -an increase in intensity by a factor of 100 corresponds to a sound level increase of 20 dB (10^2 = 100 —-> 2 * 10 = 20)

In general, the human ear is most sensitive to sounds having a frequency of about _____________________________.

1000 Hz

Speed of Sound in Water

1500 m/s

How antinodes are depicted in the diagram?

2

How many nodes are present in a string vibrating at its fundamental frequency?

2

If you hear an echo in 4 seconds, how long did it take to reach its initial distance before returning?

2 seconds

Beats

2 similar frequencies that include destructive and constructive interference

Human Range of Hearing (hz)

20 - 20,000 hz

Audible Range for humans:

20 cycles per second to 20,000 cycles per second

If the distance between the two end nodes is 2 m, what is the wavelength of the wave?

2m

How many nodes are depicted in the diagram?

3

Speed of Sound in Air

340 m/s

The speed of sound in air is approximately _______.

340 m/s

Speed of Sound in Solid

5000 m/s

What is another name for volume?

Amplitude

Describe how a sound wave is created by an object vibrating in air, Use the words *rarefaction* and *compression* correctly in your explanation.

As the object moves in one direction, it pushes against the air in that direction, forming a compression by squeezing the molecules closer together. As the object moves in the opposite direction, the air molecules spread apart, forming a rarefaction. As the object continues to vibrate, a series of compressions and rarefactions travel through the air, creating a sound wave.

What are beats? How do beats relate to music (i.e. tuning instruments)?

Beats are wave patterns from two similar frequencies. In order for music to be made, the instruments need to be tuned to the right frequency. The alternating constructive and destructive interference causes sound to be alternatively soft and loud.

How do you change the speed of sound?

Change the medium (ex: increase temperature)

Groundskeepers who mow lawns for several hours a day usually wear ear protectors, even though the loudness of the sound from the mower engine is well below the threshold of pain. Why are they wise to wear the protectors?

Damage to the ears can result from prolonged exposure to sounds that are not loud enough to cause immediate damage.

What is another name for pitch?

Frequency

What is the relationship between fundamental frequencies and harmonics?

Harmonics are integer multiples of the fundamental frequency.

Pressure Waves (2)

In a wave "compression" (where molecules are closest together), the pressure is higher than normal, whereas in an expansion (or "rarefaction") the pressure is less than normal

The speed of sound in air depends mostly upon ____________________________.

the air temperature

Beat frequency is the same as....

the difference in the two wave frequencies.

Spherical wave fronts can be treated as parallel lines when __________________________________.

they are a large distance from the source

A term for the quality of sound that gives each different musical instrument a unique sound is ___________________.

timbre

The relative amplitudes of the overtones (harmonics) for a given note are different musical instrument, which is what gives each instrument its characteristic quality or ________________.

timbre

The sound quality of an instrument is also called its _____________________.

timbre

If the observer is traveling ________________ the source, the pitch heard is _______________ than that of the emitted source frequency.

toward ; higher

Beats occur when:

two vibration sources with slightly different frequencies sound simultaneously

Frequencies above 20,000 Hz are called ______________________.

ultrasonic (many animals can hear these)

In physics, sound is defined as __________________________________.

vibrations traveling through matter

If I move very slowly away from the speaker, what changes?

volume/amplitude

The Tacoma Narrows bridge disaster is an excellent example of ______________________________________.

wind generated resonance

What do you hear?

Pitch

Pressure Waves (1)

Sound waves can be analyzed from the point of view of pressure

The Doppler effect also occurs when the source is at rest and the observer is in motion. (T/F)

T

When two notes of slightly different frequencies are sounded, beats may be heard. Explain how these beats occur.

The sound waves of the two notes interfere constructively and then destructively resulting in alternating loud and soft moments. The number of these louder-softer combinations that occur per second is equal to the difference in frequencies of the two notes.

Sound Waves in Musical Instruments

The source is set into vibration by striking, plucking, bowing, or blowing. Standing waves are produced and the source vibrates at its natural resonant frequencies. The vibrating source is in contact with the air and pushes on it to produce sound waves that travel outward. The frequencies of the waves are the same of those of the source, but the speed and wavelengths can be different

Comparing Frequencies while Tuning Instruments

To tune a piano, a piano tuner listens for beats produced between his standard tuning fork and that of a particular string on the piano, and knows it is in tune when the beats disappear.

(Wave 1- a compressed wave, Wave 2- broader wave) These waves represent sound waves created by two different vibrating objects. Assuming that both waves are traveling through the same medium, which wave is produced by the object vibrating at the higher frequency?

Wave 1. The waves are traveling at the same speed if they are in the same medium. Therefore, the wave with the shorter wavelength (Wave 1) is created by the higher frequency.

What contributed to the Tacoma Narrows Bridge Collapse?

Wind-generated resonance

Does air temperature influence the speed of sound in air? How? What equation is used to describe this relationship?

Yes, because the change in celerity depends on the medium. Therefore, the hotter the temperature, the higher the velocity (C= 331 + 0.6T)

Resonance

a force causes object to vibrate at its natural frequency

Suppose you're standing on a train platform and a train approaches then passes you. You hear:

a high pitch as it approaches and a low pitch as it passes

Sound cannot travel in the _______________________________.

absence of matter (medium).

Sound waves from a vibrating force travel in ________________ direction(s).

all

A vibrating air column in a cylindrical pipe open on both ends is capable of producing ______________________________.

all harmonics

All vibrating in a pipe open at both ends produces ____________ harmonics, while air vibrating in a pipe closed at one end produces ______________ harmonics

all; odd

The loudness of a sound depends primarily upon the ____________________ of the sound wave.

amplitude

The periodic variation in the amplitude of a wave that is the superposition of two waves of slightly different frequencies is called a ______________________.

beat

Of the following materials, sound waves travel fastest through a.) helium at 0 degrees Celsius b.) air at 0 degrees Celsius c.) copper at 0 degrees Celsius d.) air at 100 degrees Celsius

c (fastest - medium speed - slowest : solid - liquid - gas)

Sound generally travels faster through solids than through gases because the particles of a solid are ____________________________ than the particles of a gas.

closer together

A sound wave consists of a series of ____________________________.

compressions and rarefactions

The perceived loudness of a sound is measured in ___________________.

decibels

Speed of standing wave on string does/does not equal the speed of sound wave in air.

does not

Two flute players are tuning their instruments. One player sounds a tone with a pitch of 527 Hz and the other player sounds a tone with a pitch 523 Hz. How many beats per second will the players hear?

fb = f2-f1 4 = 527-523 4 beats

When a string on an acoustic guitar is struck, the hollow body of the guitar vibrates at the same frequency as a result of _____________________________.

forced vibration

When you strike a tuning fork, the sound is not very loud. When you put the base of the tuning fork on a desk top, the sound is much louder. This is called ______________________.

forced vibration

Pitch is connected with what characteristic of sound waves?

frequency

The human perception of pitch depends on a sound's _________________________.

frequency

The pitch of a pure sound is determined by the _______________________.

frequency

Natural Frequency

frequency an object wants to vibrate at

The lowest frequency of vibration of a plucked string is the string's __________________ frequency.

fundamental

1st harmonic is also known as a wave's

fundamental frequency

Frequencies below 20 Hz are called _____________________.

infrasonic (earthquakes, thunder, volcanoes)

Intensity is proportional to the ______________________.

inverse of the radius squared (1/r^2)

Resonance occurs when a force causes an object to vibrate at _______________________________.

its natural frequency

The velocity on a heavier string is _____________ and the frequency will be less for the same wavelength.

less

A sound wave is an example of a __________________ wave.

longitudinal

Suppose you are on a moving bus as it passes a stationary car in which a stereo is playing music. As the bus goes past the car, you will hear the pitch of the music become _______________.

lower

The ______________ the pitch, the __________________ the frequency, and vice versa.

lower, lower

When you hear the sound from a vehicle that is moving toward you, the pitch is higher than it would be if the vehicle were stationary. The pitch sounds higher because the sound waves arrive ___________________ frequently.

more

Every object sounds different when it's disturbed because it has a _______________________________ at which it vibrates using little energy.

natural frequency

When an orchestra is warming up and are at the same exact frequency, the musicians would hear ____________ beats.

no

What is the relationship between volume (or loudness) and frequency?

none

With a fixed source and a moving observer, the distance between wave crests, the wavelength, is __________________.The velocity of the crests with respect to the observer is _________________.

not changed ; changed

Is a string of a guitar an open or closed vibration?

open

The _______________ of a sound refers to whether it is high, like the sound of a piccolo or violin, or low, like the sound of a bass drum or string bass.

pitch

The frequency of a sound wave determines its ____________________________.

pitch

The measured intensity of sound depends on both the distance from the source and the ___________________ of the sound source.

power

What is the Doppler effect? How does it affect pitch experienced by an observer?

It is a shift in frequency based on motion. When the source of the sound waves are closer, the pitch/frequency is higher, but when the source is farther, the pitch/frequency is lower Example: A train blows its horn passing by --> sound waves compress and go up in pitch for the stationary listener.

What is sound? What kind of waves are sound waves?

It is a wave created by a vibrating source transmitted through a medium: longitudinal

Sound waves are what kind of waves?

Longitudinal

__________________ is related to the intensity (energy per unit time crossing unit area) in a sound wave.

Loudness