Are you taking Phys. 1240, The Physics of Sound and Music, for credit? A ) yes B ) no

1. Are you taking Phys. 1240, The Physics of Sound and Music, for credit?A) yesB) no

2. Welcome to PHYS 1240 Sound and Music Professor Allen Hermann Cell Phones off Clickers on

3. M T W R F

4. GradesMid-term exam……….25%Final exam……………...35%Homework………………30%Class participation (clicker) ..........…….10%Total……………………….100%

5. Exam dates:Wed. July 23 midtermFri. Aug.8 final

6. CT 1.0.1 What instrument have you played? (If you have played several, which one the most?) • piano • guitar • any other instrument with strings • any wind instrument • never played any instrument

7. What is sound? Sound is produced by periodic vibrations, but we need a medium as well for the sound to propagate. Sound is different from light in that it cannot travel in empty space. So an explosion of a distant star would never be heard by us on earth. Sound travels as mechanical waves, through solids liquids and gases. So to understand sound, we must understand periodic vibrations or oscillations(the source of sound), the movement of the disturbance which these vibrations cause through a material medium (sound wave), and the reception of this disturbance by, e.g. the ear.

8. Graphs

11. The slope is the speed (discuss the term “velocity”).In the last slide the initial slope corresponds to about 180 m traversed in about 3 minutes (180 sec), or the initial speed is about 180m/180 sec= 1 m/s

12. In the period between second 6 and second 9, the student’s speed isa) faster than the initial speedb) slower than the initial speedc) the same as the initial speed

13. PhET simulationsyou should gain access at phet.colorado.edugo to Play with SIMSwe will do The Moving Man

14. To learn about Periodic Vibrations or Oscillations, we must first learn about Forces

18. A little about Vectors

20. The bigger the weight (force on the spring), the more the spring extends and the more the spring “pulls back”, i.e. the greater the restoring force.We can write the restoring force Fr is proportional to the extension x,Fr=-kx

22. PhET Masses and Springs

23. PhET Pendulum Lab

25. Simple Harmonic Motion • Position x vs. time t • Definition of period T • Definition of amplitude A

26. SHM Systems

30. Let the period be T (in seconds). The number of times the vibrating source executes SHM in one second (i.e. the frequency, f, units of Hz)) is 1/T.For example, if T is 0.1 s, f is just 1/0.1=10 Hz

31. Frequency and Period f = 1/T or T = 1/f or f T =1 T period, in seconds (s) f = frequency in Hertz (Hz) Metric prefixes: centi- (c), milli- (m), micro- (m) kilo- (k), mega- (M)

35. CT 2.1.8 Amplitude Looking at the following waveform, what is the period? • 1 sec • 2 sec • 1 m/s • 2 m/s • Not enough information time (sec) 0 1 2

36. CT 2.1.2 When the amplitude of an oscillating object is doubled, the period becomes: • twice as big • 1/2 as big • Stays the same • 1/4 times as big • Not enough information to decide When the frequency is doubled, the period becomes…

37. Pulses and Waves

38. Phet Wave on a StringPulse propagation

41. CT 1.3.3x I grab the left end of a LONG string and wiggle it up and down. There is a purple painted spot somewhere on the string. What choice below best shows the motion of the purple spot? (up and down) (pushed steadily to the right) (left and right) (no motion) (circular path)

42. PhET Wave on a StringPeriodic Oscillations or Vibrations

47. Wave velocity for a periodic vibrationLet the wavelength be λand the frequency of the vibration be f.The wave velocity v is just V=λ/T, orV= λf

48. CT 2.1.10 Amplitude The wavelength, λ, is 10 m. What is the speed of this wave? • 1 m/s • 7 m/s • 10 m/s • 15 m/s • None of the above/not enough info? Time (sec) 0 1

49. What determines the velocity of a transverse pulse or wave on a string (v=λf simply constrains f and λ) ?The velocity is determined by the tension T ( a force in N) applied to the string, and the mass per unit length μ ( in kg/m).