ISNS 3371 - Phenomena of Nature The second test will be next Thursday, March 15 at the regular class time. We will have two review sessions, one at 1:00

ISNS 3371 - Phenomena of Nature

The second test will be next Thursday, March 15 at the regular class time.We will have two review sessions, one at 1:00 PM today (Tuesday) and one at 1:00 PM tomorrow (Wednesday), both in FN 2.212 on the SW corner of Founder’s North. The test will cover any topic we have discussed in class. These include:

Heat, TemperatureTransfer of heat - Conduction, ConvectionChange of state of matterGases - gas laws: Boyle, Charles, Guy Lusac, GeneralLaws of ThermodynamicsArchimedes’ PrincipleBernoulli EffectWaves, Properties of WavesStanding WavesSound WavesResonance, InterferencePitch vs. Frequency,Loudness vs. Intensity


Standing Wave vs Traveling Wave

Traveling wave - a type of wave pattern which is seen traveling through a medium - crests are seen to propagate through the medium

Standing wave - a wave reflected in such a way that it does not propagate.

node: point where particles are at rest.

antinode: point where particles execute maximum periodic motion, (maximum amplitude).

Standing wave modes arise from the combination of reflection and interference.


Two traveling waves which exist in the same medium will interfere with each other. If amplitudes add - constructive interference. If they are "out of phase" and subtract - destructive interference

Constructive interference is the combined result of two waves that are exactly in phase. In other words, both of the waves are operating at the exact same frequency and both of them crest at the exact same moment.

Interference

Destructive interference is the combined result of two waves that are out of phase. In other words, When the crest of one wave occurs at the same time as the trough of another wave.

ISNS 3371 - Phenomena of Nature Interference

Constructive - waves add in phase, producing larger peaks than any wave alone.

Destructive - waves add out of phase, producing smaller peaks than a single wave alone.


Interference of Waves

Dark lines are crests and light lines are troughs - interference creates a pattern.

Constructive interference occurs at A and B - crests are twice as highDestructive interference occurs at C, D, E, and F - the waves cancel out


Reflection

The string appears to vibrate in segments or regions and the fact that these vibrations are made up of traveling waves is not apparent - hence the term "standing wave".

ISNS 3371 - Phenomena of NatureProducing a Standing WaveWhen a wave of the proper frequency is produced on a string, a node occurs at the end of the string and the interference of the incident wave and the reflected wave occur in such a manner that there are specific points along the medium which appear to be standing still.


Sound Waves

• Longitudinal or compressional wave

• Vibrating source pushes air molecules adjacent to it closer together - compresses them. This motion is handed on from molecule to molecule.

Thus is generated a compressional wave that propagates through the air.

Each compression is followed by a rarefaction, a region of lesser density.

• The wave travels through the air but each molecule only moves forth and back in its local position.


Propagation of a compression

along the particles of a

medium.

Propagation of a rarefaction

along the particles of a

medium.


A vibrating tuning fork - capable of creating a longitudinal sound wave. As the tines of the fork vibrate back and forth, they push on neighboring air particles. The forward motion of a tine pushes air molecules horizontally to the right and the backward retraction of the tine creates a low pressure area allowing the air particles to move back to the left. Because of the longitudinal motion of the air particles, there are regions in the air where the air particles are compressed together and other regions where the air particles are spread apart - compressions and rarefactions. The compressions are regions of high air pressure while the rarefactions are regions of low air pressure.

Tuning Fork

QuickTime™ and aGIF decompressor

are needed to see this picture.


Sound wave - consists of a repeating pattern of high pressure and low pressure regions moving through a medium.

Sound - A Pressure Wave

A plot of pressure vs. time appears as a sine curve. The crests of the sine curve correspond to compressions; the troughs correspond to rarefactions; and the "zero point" corresponds to the pressure which the air would have if there were no disturbance moving through it.


When a pressure wave reaches the ear, a series of high and low pressure regions impinge upon the eardrum. The arrival of a compression or high pressure region pushes the eardrum inward; the arrival of a low pressure regions pulls the eardrum outward. The continuous arrival of high and low pressure regions sets the eardrum into vibrational motion.

The Ear

The eardrum is attached to the bones of the middle ear - the hammer, anvil, and stirrup. As these bones begin vibrating, the sound signal is transformed from a pressure wave traveling through air to the mechanical vibrations of the bone structure of the middle ear. These vibrations are then transmitted to the fluid of the inner ear where they are converted to electrical nerve impulses which are sent to the brain.


If you put your finger gently on a loudspeaker you will feel it vibrate - if it is playing a low note loudly you can see it moving. When it moves forwards, it compresses the air next to it, which raises its pressure. Some of this air flows outwards, compressing the next layer of air. The disturbance in the air spreads out as a travelling sound wave. Ultimately this sound wave causes a very tiny vibration in your eardrum.

Loudspeakers


“In Space, No One Can Hear You Scream”

Without a medium such as air or water, there is no sound.


Speed of sound

• air: 1100 ft/sec(750 mph)

• water: 4700 ft/sec• Steel: 15000 ft/sec

• Air is a non-dispersive mediumAll sound frequencies travel at the same speed.

• Speed is a function of temperature.It increases 1.1 ft/sec for each degree F rise in air temperature.


Properties of Sound Waves

Pitch: Highness or lowness of soundRelated to frequency of sound wave.

Intensity: Average rate at which acoustic energypasses a point.

Related to amplitude of sound wave.

Loudness: Magnitude of sensation of sound asjudged by an individual.

Subjective aspect of hearing process.


Frequency of wave

• Frequency of sound wave is related to pitch of sound• Low frequency - low pitch• High frequency - high pitch• Range of audible frequencies

20 hertz to ~18,000 hertz

(1 hertz = 1 cycle per second)


Frequency of notes on staff (C):

66, 132, 264, 528, 1056 (hertz)

Each succeeding note is 1 octave higher and has twice the frequency

Standard frequency: A = 440 hertz.


Interval Frequency Ratio

Examples

Octave 2:1 512 Hz and 256 Hz

Third 5:4 320 Hz and 256 Hz

Fourth 4:3 342 Hz and 256 Hz

Fifth 3:2 384 Hz and 256 Hz

Certain sound waves when played (and heard) simultaneously will produce a particularly pleasant sensation when heard, are are said to be consonant. Such sound waves form the basis of intervals in music.

Many people, especially those who have been musically trained, are capable of detecting a difference in frequency between two separate sounds which is as little as 2 Hz.

http://upload.wikimedia.org/wikipedia/en/4/49/Interval_numbers.gif


Intensity and loudness

Physical vs psychological characteristic of sound - no direct relationship.

Intensity related to amplitude of sound wave, or to the pressure variation in the sound wave.

Loudness depends on intensity, frequency and sensitivity of ear.

Intensity is proportional to the amount of sound energy that is flowing past a given point. The greater the amplitude of vibrations of the particles of the medium, the greater the rate at which energy is transported through it, and the more intense that the sound wave is. Intensity is the energy/time/area; and since the energy/time ratio is equivalent to the quantity power, intensity is simply the power/area. Typical units for expressing the intensity of a sound wave are Watts/meter2.


Sound intensity

Sound pressure:Minimum audible: one billionth of atmospheric pressure - corresponds to an intensity of 1 X 10-12 W/m2.Threshold of pain: one thousandth of atmospheric pressure - 1 X 101 W/m2

Range of audible pressure changes is 1 million - 16 orders of magnitude in intensityScale to measure these is called decibel scale (db).

Since the range of intensities which the human ear can detect is so large, the scale which is frequently used by physicists to measure intensity is a scale based on multiples of 10 - a logarithmic scale. The scale for measuring intensity is the decibel scale.

The threshold of hearing is assigned a sound level of 0 decibels (abbreviated 0 dB). A sound which is 10 times more intense (1 X 10-11 W/m2) is assigned a sound level of 10 dB, a sound 100 times more intense (1 X 10-10 W/m2) is assigned a sound level of 20 db, etc…


Source Intensity Intensity Level # Times Greater Than TOH

Threshold of Hearing (TOH)

1 X 10-12 W/m2 0 dB 1

Rustling Leaves 1 X 10-11 W/m2 10 dB 101

Whisper 1 X 10-10 W/m2 20 dB 102

Normal Conversation 1 X 10-6 W/m2 60 dB 106

Busy Street Traffic 1 X 10-5 W/m2 70 dB 107

Vacuum Cleaner 1 X 10-4 W/m2 80 dB 108

Large Orchestra 6.3 X 10-3 W/m2 98 dB 109.8

Walkman at Maximum Level

1 X 10-2 W/m2 100 dB 1010

Front Rows of Rock Concert

1 X 10-1 W/m2 110 dB 1011

Threshold of Pain 1 X 101 W/m2 130 dB 1013

Military Jet Takeoff 1 X 102 W/m2 140 dB 1014

Instant Perforation of Eardrum

1 X 104 W/m2 160 dB 1016

Documents

ISNS 3371 - Phenomena of Nature The second test will be next Thursday, March 15 at the regular class time. We will have two review sessions, one at 1:00