1Phys 1240: Sound and Musicwww.colorado.edu/physics/phys1240LAST: waves and soundTODAY: waves and SHMNEXT: resonance and instrumentsREAD: 3.2-3.3(New CAPA is out)Remember help room hours andproblem solving sessions!CT1.3.xxIf a big collision occurs in deep,empty outer space (two asteroidssmall into one another, surroundedby “vacuum”),Does it make a sound?A) SureB) Sure (if there’s an astronaut there to hear it)C) No.“In space no one can hear you scream” (“Alien” ads, c. 1979)CT 2.1.6The air warms up by 20o C. It turns out that thisinstrument (like most wind instruments) producessound waves of a particular waveleng th.So, changing the temperature will not changethe wavelength of sound waves produced bythis instrument (noticeably.)What will change?a) Frequencyb) Speedc) Bothd) Neithere) ??Speed = wavelength*frequencyv = λ f CT 2.1.7We know that pressure changes (as timegoes by) for sound waves.What changes (as time goes by) for gentlewater waves on a pond?a) The water densityb) The water temperaturec) The water level or heightd) The water molecules’ position in thedirection of wave propagatione) Nothing about water waves vary with time2CT 2.1.8Amplitudetime (sec)1 2Looking at the following waveform, whatis the period?a) 1 secb) 2 secc) 1 m/sd) 2 m/se)Not enough informationCT 2.1.9Looking at that same wave (shown againbelow), what is its speed?a) 1/2 m/sb) 2 m/sc) 5 m/sd) 20 m/se) Not enough informationAmplitudeTime (sec)1 2Now given that λ=10 m what is the speed ofthe wave?The wavelength, λ, is 10 m. What is thespeed of this wave?a) 1 m/sb) 7 m/sc) 10 m/sd) 15 m/se) None of the above/not enough info?CT 2.1.101Time (sec)AmplitudeCT 2.2.1An oscilloscope presents a graphicalrepresentation of:a) Amplitude vs. Positionb) Wavelength vs. Timec) Voltage vs. Positiond) Voltage vs. Timee) Wavelength vs Amplitude3CT 2.2.3What is the period of this wave?a) t1b) t2c) Not at all definedd) Not well defined, but t1 is the bestanswere) Not well defined, but t2 is the bestanswert=0t1t2AmptimeCT 2.2.4What is the period?a) t1b) t2c) t2-t1d) t3-t1e) None of the abovet1t2t3Amptime0Simple harmonic motion“Harmonic” motion: periodicIf the force pulling you backdoubles when you stretchtwice as farSimple harmonic motion“Harmonic” motion: periodicIf the force pulling you backgrows linearly with how farfrom equilibrium you are=> SIMPLE harmonic motiondisplacementtime4CT 2.4.1Which of the following is necessary to makean object oscillate?i. A stable equilibriumii. Little or no frictioniii. A disturbancea) i. onlyb) ii. Onlyc) iii. Onlyd) i and iii onlye) all threeGiven the above, will the motion be“Simple Harmonic Motion”?springsMass on an (ideal) spring is “SHM”(simple harmonic…)The frequency is completelydetermined** by the** the Amplitude does not matter!!•Mass (m)•Spring stiffness (K)(bigger K means more stiff)Freq. = (constant) * √ ( K/m)Does this make sense?What if mass is greater?… spring is floppier? (smaller K)CT 2.4.5Freq. = (constant) * √ ( K/m)A mass on a spring oscillates with acertain amplitude and a certainfrequency. If the mass is replacedwith one 4 times heavier, whathappens to the frequency…A doublesB: increases by 4C: halves.D: decreases by 4E: None of these/not sureWhat happens to the
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