Phys 1240: Sound and Musicwww.colorado.edu/physics/phys1240LAST: Intro, course logisticsProduction, propagation, perceptionTODAY: pitch/frequencySpeed of soundNEXT: waves and pressure wavesREAD: Hall 1.5, 2.1, 2.2Online homework Tues - see web.(CAPA next Thursday… pick one upin basement)[email protected] you have a clicker?A) Yes, I do!B) Not yet…(Don’t forget to register it, there’s alink in the “announcement box”on our home page)CT 1.0.1How do you think you will learn physics thebest?a) Listening to lectureb) Reading the textbookc) Doing the homeworkd) Discussing with otherse) Other…We cannot teach you physics (!)Physics is not a collection of facts - it’s away of thinking.Only you can teach yourself to think!Analyzing, sense making, applyingconcepts , solving problemsCT 1.1.2The following sound would be classified as:a) Musicalb) Speechc) Noised) Organized sounde) TransientPitch & loudness(Perception)Pitch: “how low or high” For musicians: bass or trebleLoudness: sensation of strengthCT 1.2.2If I whack a ruler hanging off thedesk, I can make a “note”.What happens if I move it back soless hangs off the edge, but Iwhack it just as hard?A) Pitch , loudness similarB) Pitch similar, loudnessC) Pitch , loudnessD) Pitch , loudness similarE) Something elseWHY?CT 1.2.3What determines pitch?Which is the most important featureof the instrument/source ofsound?A) Length/sizeB) “Bendability”/rigidityC) Heaviness/density of materialD) Amplitude (how hard it is struck)E) More than one of the aboveA-B: very (equally) importantC: Depends!D is a special case… but usuallydoes NOT matter (much).CT1.2.4Let’s fill the Tibetan singing bowl withwater. What happens to the pitch ofthe tone it makes?A) goes upB) goes downC) pretty much unchangedD) no way to know this withouttryingWhy?Propagation:• Speed. (How could we measure it?)• Medium (Does it matter? Come back tothis very soon)CT 1.4.7Which sounds travel the fastest through air?a) Higher pitchb) Lower pitchc) Louder soundsd) Quieter soundse) They all travel at the same speedAnd a darn good thing…Speed of sound(344 m/s in room temperature air.)CT 1.4.1Approximately how close is a thunderstormif you see lightning flash and hear a clashof thunder after counting up to 6 seconds?(the speed of sound is 344 m/s)a)0 kmb)1 kmc)2 kmd)6 kme)None of theseUnits:1 meter is 3.3 feet! = 344 m " 1So, 344 m/s is the same as 1135 feet/s (more than 3 football fields/s)= 770 mi/hr! = 344 m " 3.3 feet1 m ! = 1135 feet 344 meterCT 1.4.2You are traveling on a commercial airplane (saya Boeing 757). Relative to the speed of soundyou are traveling:a) much slower than soundb) a little slower than soundc) the same speed than soundd) a little faster sounde) much faster soundCT 1.4.4In which of the following venues can you noticea difference between the music you perceiveand the movements of the musicians (i.e. canyou tell that the sound has traveled a distance?)a) The rear of the Fox Theaterb) Pepsi Centerc) Red Rocks amphitheaterd) All of the aboveTextbook says about 20 meters (about 60 feet,about the width of the grass field in thestadium) is where most people start tonotice it.CT 1.4.5In a 32 o C room sound travels…a) > 344 m/sb) 344 m/sc) < 344 m/sSpeed depends on the temperatureDepends on the medium(Faster through solid metal thanthrough air, e.g!)What if the room is 32o F? Does the soundtravel faster or slower than a 32o C room?a) Fasterb) Slowerc) Same speed(speed is 344 m/s at 20 °C) Temperature dependence?• Speed of sound goes up byabout .6 m/s for every degreeCelsius increase.Tune clarinet in an air conditionedroom (20 °C)Go outside (HOT) 40 C (>100°F!)Speed is (40-20)*.6 m/s faster = 12 m/s(12/344 = 3% faster)
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