Presentation on theme: "Chapter 15 Sound If a tree falls in the forest and no one is there to"— Presentation transcript:
1 Chapter 15 Sound If a tree falls in the forest and no one is there to hear it, does it make a sound?A sound wave is a pressure variation that istransmitted through matter.Sound is a longitudinal and a mechanical wave
2 Chapter 15 Sound The speed of sound in air at 0º C is 330 m/s and increases at .6 m/s for each degree increasein temperature.In general, the speed of sound is faster in solidsand in liquids because the molecules are closertogether.The frequency and the wavelength are relatedby the equation v = f.
3 Chapter 15 Sound Loudness: The loudness of a sound depends primarily on the amplitude of the pressure wave.Loudness is measured in decibels.Frequency: The number of cycles per second.The human ear can detect frequencies between20 and 20,000 Hz.Frequency and loudness are not related.
4 Chapter 15 Sound Find the frequency and the period of a sound wave moving in air at room temperature (20º C)with a wavelength of .8 m.v = f or f = v/f = (330 m/s + (.6 m/s)(20))/.8 mf = 342 m/s /.8 m= Hz
5 Chapter 15 Sound If a sound is made and hear the echo from a wall 3 seconds later, how far away is the wall?The temperature is 30º C.d = vtd = (330 m/s + (.6 m/s)(30) ( 1.5 s)d = (348 m/s)(1.5 s) = 522 m
6 Chapter 15 Sound Doppler Shift: A change in sound frequency due to the relative motion of either the sourceor the detector.Demonstration
10 Chapter 15 Sound Raising and lowering the tube changes the length of the air column. When theair column is in resonancewith the tuning fork, thesound is the loudest,
11 Chapter 15 Sound Musical Instruments String -Vibration of a string resonate a sounding board.Brass - Vibration of lipsReed - Vibration of a column of airPercussion - Vibration of an object, vibrates a column ofair.
12 Chapter 15 Sound Columns of /4, 3/4, 5/4, … will all be in resonance with a tuning fork.Demonstration
13 Chapter 15 Sound Columns of /2, , 3/2, 2, … will all be in resonance with a tuning fork.
14 Chapter 15 Sound A tuning fork with a frequency of 392 Hz is found to cause resonances in an air columnSpaced by 44.3 cm. The air temperature is27º C. Find the velocity of sound in air at thattemperature.f = 392 Hzl = 44.3 cmResonances are spaced by one-halfwavelength so = 2lV = f = f(2l) = (392 Hz)(.866m) = 347 m/s
15 Chapter 15 Sound The frequency of a tuning fork is unknown. A student uses an air column at 27°C and findsresonances spaced by 39.2 cm. What is thefrequency of the tuning fork?v = 347 m/sl = 39.2 cmResonances are spaced by one-halfwavelength so = 2lF=v/ = 347m/s/.784 m = 443 Hz
16 Chapter 15 Sound Higher frequencies which are Odd-number multiples of thefundamental frequency arecalled Harmonics.
17 Chapter 15 SoundThe ear consists of three basic parts -the outer ear, the middle ear, and the inner ear.Each part of the ear serves a specific purpose in the task of detecting and interpreting sound.The outer ear serves to collect and channel soundto the middle ear. The middle ear serves to transformthe energy of a sound wave into the internal vibrationsof the bone structure of the middle ear and ultimatelytransform these vibrations into a compressional wave inthe inner ear. The inner ear serves to transform the energyof a compressional wave within the inner ear fluid into nerve impulses which can be transmitted to the brain.
19 Chapter 15 Sound Sound Quality Chord Several pitches played together. Dissonance An unpleasant set of pitches.Consonance A pleasant set of pitches.Octave The interval between twofrequencies with a ratio of 2:1Pythagoras noted that pleasing sounds occurredwhen the strings have lengths in smallwhole-number ratios, 1:2, 2:3, etc.