1Phys 1240: Sound and MusicLAST: diffraction, dopplerTODAY: outdoor sound, intensity andloudnessNEXT: more on decibelsREAD: 5.3 and 5.4CAPA 5 in bins, due in TWO weeks,(Thursday AFTER the break)So… no help sessions today.If you want to meet, email any ofus!4.4.2A child is swinging on a swingtowards a person blowing a whistle.At which position will the pitchsound the highest to the child?d. The pitch is the same at all thepoints.Whistlera.b.c.endstart4.4.4The picture below shows a travelingobject that is emitting a sound. Thereis a person at point A and a person atpoint B.Which way is the sound traveling?a) Towards the rightb) Towards the leftc) All directionsd) No directions, this is a standingwavee) ??A BWho hears the higher pitch?A B) C) They hear the same pitchD) ??4.3.1Adding a shell around a performerat an outdoor show…a) Improves the music no matterwhere the performer is positionedor where the audience sitsb) Subtly alters the pitch of thesound, making it more pleasing tonormal hearingc) Diffracts the music better,allowing bigger audience to heard) Is mostly for aestheticpurposes/protection from raine) Could increase the loudness forthe audience, depending on wherethe performer is positioned withinthe shell.2Outdoor music• Sound is generally weaker thanindoors (why?)• Shell reflects sound, can improve– Volume for audience– Consistency of sound at various spots– Acoustics for the performers(Why?)Where should the performer stand toget the maximum benefits out of thiscircular shell?d)Somewhere elsee)There is no difference4.3.2a.b.c.DiscussionHow/why do each of thefollowing improve outdoormusic performances?• Stadium seating• Shell behind the performers• Roof above the performers• Locating the musicianshalfway between a curved walland that wall’s center ofcurvatureWould the amplitude on this graph mostlikely be…a) Velocity amplitudeb) Displacement amplitudec) Pressure amplituded) Wavelength amplitudee) None of the above5.1.1Position (m)Time (s)Which amplitude have we been mostconcerned with when studying music so far?(why?)3Describing sound strength Amplitude tells you“overpressure” => extra force/areaCan be very useful…But sometimes we are moreinterested in something else…5.1.2Which sound is stronger?a) The one on the leftb) The one on the rightc) They are the same strengthd) You can’t tellOver Pressure (N/m2)Time(s)Time(s)Over Pressure (N/m2)5.1.3Looking at the following two graphswhat can you say about the energycarried by the wave?a)The energy is larger in I.b)The energy is larger in II.c)The energy is the same in bothd)You can’t tell anything about theenergy from these graphse)What does energy have to dowith music?Over Pressure (N/m2)Time (s)Over Pressure (N/m2)Time (s)I.II.Measuring…FORCE => NewtonsPRESSURE => Newtons/m2WORK or ENERGY => JoulesRecall:Work = force * distance(So, 1 Joule = 1 Newton* 1 meter)45.1.4If you do overall positive work on asystem, what happens to the totalenergy of that system?a) Energy increasesb) Energy decreasesc) Energy is conserved, it does notchange.d) ??Mass on a spring• If pull it twice as far => need twice the forceWork = force*distancePull it twice as far => “twice the force” * “twice the dist.” => FOUR times the work!Energy of oscillating objectsgrows like (amplitude)2CT 5.1x.1You pull a mass on a spring 1 cm andlet it go. Suppose it has 2 Joules (2 J)of energy.If you now pull it 10 cm and let it go,how much energy does it have?A) 2 JB) 10 JC) 20 JD) 100 JE) 200
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