Slide 1 / 81 Slide 2 / 81 Algebra Based Physics Sound Waves 2015-12-01 www.njctl.org https://www.njctl.org/video/?v=mWvx3TvYl_Y Slide 3 / 81 Slide 4 / 81 Table of Contents Click on the topic to go to that section Characteristics of Sound · Characteristics of Sources of Sound · Sound Open Tubes · Closed Tubes · Interference · Doppler Effect · Return to Table of Contents Slide 5 / 81 Slide 6 / 81 Characteristics of Sound 1 Sound waves travel with the greatest velocity in Sound can travel through any kind A gases of matter, but not through a vacuum. B liquids The speed of sound is different in different materials; in general, it C solids is slowest in gases, faster in liquids, and fastest in solids. The speed depends somewhat on temperature, especially for gases. Click here for a video on sound waves moving in various materials https://www.njctl.org/video/?v=wYD-HDP3rYc
Slide 7 / 81 Slide 8 / 81 Characteristics of Sound 2 Which of the following frequencies can be perceieved by humans? Loudness: related to intensity of the sound wave (as the A 10 Hz volume increases, the amplitude of the waves increases) Sound waves are produced by vibrations that occur B 1,000 Hz between 20 to 20,000 vibrations per second. C 100,000 Hz Pitch: related to frequency. Audible range: about 20 Hz to 20,000 Hz; upper limit decreases with age Ultrasound: above 20,000 Hz; see ultrasonic camera focusing below Infrasound: below 20 Hz Click here for a video on how our vocal cords vibrate and produce sound https://www.njctl.org/video/?v=G_q8CixnJhc https://www.njctl.org/video/?v=SmsSgzQZHB8 Slide 9 / 81 Slide 10 / 81 Intensity of Sound: Decibels Intensity of Sound: Decibels An increase in sound level of 3 The intensity of a wave is the energy dB, which is a doubling in transported per unit time across a intensity, is a very small unit area. change in loudness. In open areas, the intensity of The human ear can detect sounds sound diminishes with with an intensity as low as 10 -12 distance: W/m 2 and as high as 1 W/m 2 . Perceived loudness, however, is not proportional to the intensity. However, in enclosed spaces this is complicated by reflections , and if sound travels through air the higher frequencies get preferentially absorbed . https://www.njctl.org/video/?v=X1EZaV08wbI Slide 11 / 81 Slide 12 / 81 3 Doubling the distance from a sound source will change 4 As you walk toward a sound source the volume will the intensity (volume) by a factor of the original value A increase A 2 B decrease B 4 C will not change C 1/4 D 1/2 https://www.njctl.org/video/?v=hMqOE3knLuc https://www.njctl.org/video/?v=_Kf1BCv-awE
Slide 13 / 81 Slide 14 / 81 5 Reducing the distance from a sound source to one half 6 Cutting the distance from a sound source by a factor of the original value will change the intensity (volume) by 1/3 will change the intensity (volume) by a factor of the what factor? original value A 2 A 3 B 4 B 9 C 1/3 C 1/4 D 1/9 D 1/2 https://www.njctl.org/video/?v=NSEGauhtHFo https://www.njctl.org/video/?v=92weEIoT6aY Slide 15 / 81 Slide 16 / 81 The Ear and Its Response; Loudness The Ear and Its Response; Loudness Outer ear: sound waves travel down the ear canal to the eardrum, which vibrates in response Middle ear: hammer, anvil, and stirrup transfer vibrations to inner ear Inner ear: cochlea transforms vibrational energy to electrical energy and sends signals to the brain Click here for a video on hearing https://www.njctl.org/video/?v=lGCtTI9PIi0 Slide 17 / 81 Slide 18 / 81 The Ear and its Response; Loudness The ear’s sensitivity varies with frequency. These curves translate the intensity into sound level at different frequencies. Sources of Sound Return to Table of Contents
Slide 19 / 81 Slide 20 / 81 Sources of Sound: Sources of Sound: Vibrating Strings and Vibrating Strings and Air Columns Air Columns The strings on a guitar can Musical instruments produce sounds in various ways – be effectively shortened by vibrating strings, vibrating membranes, vibrating metal or fingering, raising the wood shapes, vibrating air columns. fundamental pitch. The vibration may be started by plucking, striking, The pitch of a string of a given bowing, or blowing. The vibrations are transmitted to the length can also be air and then to our ears. altered by using a string of different density. Click here for a video on guitar string pitch https://www.njctl.org/video/?v=L7WFbK2vDOQ Slide 21 / 81 Slide 22 / 81 Sources of Sound: Sources of Sound: Vibrating Strings and Air Columns Vibrating Strings and Air Columns Length Pitch A piano uses both methods to cover its A piano uses both more than seven-octave methods to cover its range – the lower strings more than seven-octave (at bottom) are both range – the lower strings much longer and much (at bottom) are both thicker than the higher much longer and much ones. thicker than the higher ones. The product of length and pitch is a constant. Observe relationship between wavelength and frequency Slide 23 / 81 Slide 24 / 81 Sources of Sound: Vibrating Strings and Air Columns Wind instruments create sound through standing waves in a column of air. Open Tubes Click here for a video on sound in air columns Return to Table of Contents
Slide 25 / 81 Slide 26 / 81 Sources of Sound: Sources of Sound: Open Tubes Vibrating Strings and Air Columns The general equation for the wavelength of an open tube is: A tube open at both ends (most wind instruments) has pressure nodes, and therefore displacement antinodes, at the ends. Where n is the number of nodes. Slide 27 / 81 Slide 28 / 81 Sources of Sound: Sources of Sound: Vibrating Strings and Air Columns Vibrating Strings and Air Columns If instead of air displacement, you look at air pressure variation the nodes and antinodes are switched. An open tube has the same harmonic structure as a string. Slide 29 / 81 Slide 30 / 81 8 A sound wave resonates in a tube of length 2m with two 7 A sound wave resonates in a tube of length 2m with two open ends. What is the lowest resonating frequency of open ends. What is the wavelength of the lowest the tube if the speed of sound in air is 340m/s? resonating frequency of the tube? A 1m B 1.5m C 2m D 4m E 8m https://www.njctl.org/video/?v=5jrEfQWG1c4 https://www.njctl.org/video/?v=6PG2uub_B10
Slide 31 / 81 Slide 32 / 81 9 A sound wave resonates in a tube of length 6m with 10 A sound wave resonates in a tube of length 6m with two two open ends. What is the wavelength of the lowest open ends. What is the lowest resonating frequency of resonating frequency of the tube? the tube if the speed of sound in air is 340m/s? A 6m B 12m C 18m D 24m E 3m https://www.njctl.org/video/?v=WcX3uoVJMNw Slide 33 / 81 Slide 34 / 81 Sources of Sound: Vibrating Strings and Air Columns A tube closed at one end (some organ pipes) has a displacement node (and pressure antinode) at the closed end. Closed Tubes Return to Table of Contents https://www.njctl.org/video/?v=ACs3T0MIIvQ Slide 35 / 81 Slide 36 / 81 Sources of Sound: Closed Tubes 11 A sound wave resonates in a tube of length 2m with one open end. What is the wavelength of the lowest resonating frequency of the tube? A 1m L L L L B 1.5m # 1 C 2m D 4m E 8m https://www.njctl.org/video/?v=UeTF68F8BEg
Slide 37 / 81 Slide 38 / 81 12 A sound wave resonates in a tube of length 2m with 13 A sound wave resonates in a tube of length 2m with one one open end. What is the lowest resonating frequency of open end. What is the next lowest resonating frequency the tube if the speed of sound in air is 340 m/s? of the tube if the speed of sound in air is 340 m/s? https://www.njctl.org/video/?v=pnzOORrgTlo https://www.njctl.org/video/?v=5HMxPu2VX14 Slide 39 / 81 Slide 40 / 81 14 A sound wave resonates in a tube of length 1/2m 15 A sound wave resonates in a tube of length 1/2m with with one open end. What is the wavelength of the lowest one open end. What is the lowest resonating frequency resonating frequency of the tube? of the tube if the speed of sound in air is 340 m/s? A 1m B 1.5m C 2m D 4m E 8m https://www.njctl.org/video/?v=M-SXIBZF8EM https://www.njctl.org/video/?v=0AoPbUT-PrA Slide 41 / 81 Slide 42 / 81 Quality of Sound, and Noise; 16 A sound wave resonates in a tube of length 1/2m with Superposition one open end. What is the next lowest resonating frequency of the tube if the speed of sound in air is 340 So why does a trumpet sound different from a flute? The answer lies in overtones – which ones are present, and how strong m/s? they are, makes a big difference. The plot below shows frequency spectra for a clarinet, a piano, and a violin. The differences in overtone strength are apparent. Click here for a video on sound and timbre https://www.njctl.org/video/?v=pLsi8ycnhUY https://www.njctl.org/video/?v=HeW5O0SdQ08
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