Physics Chapter 5, Section 4 Sounds from Vibrating Air

Mar 14, 2012 HW: 5.4 PTG p 526 #1, 4-6, Due Tuesday  Learning Objective  Explain how sound is produced by longitudinal compression waves  Write a conclusion that includes IV, DV, evidence, and the big idea  Success Criteria  Identify standing waves in different kinds of air-filled tubes  Observe how pitch changes with the length of the tube  Observe the effect of closing one end of the tube on the pitch of the sound  Observe sound bending around corners and spreading  Relate observations of pitch to drawings of standing waves  Organize observations to find a pattern  Do Now  Write LO and SC on new left page  p 518 WDYS/WDYT  Agenda  Do Now  Investigation 5.4  Summary

Investigation 5.4 pg  Part A (groups)  with straws  4, 5 with test tubes  Part B  1 - Class demo  2 - with group  Part C  In groups  Set up Notebook  Ok with Spencer  Set up Notebook  Ok with Spencer  Set up Notebook  Ok with Spencer

Mar 16, 2012 HW: HW: 5.4 PTG p 526 #1, 4-6, Due Tuesday  Learning Objective  Explain how sound is produced by longitudinal compression waves  Write a conclusion that includes IV, DV, evidence, and the big idea  Success Criteria  Identify standing waves in different kinds of air-filled tubes  Observe how pitch changes with the length of the tube  Observe the effect of closing one end of the tube on the pitch of the sound  Observe sound bending around corners and spreading  Relate observations of pitch to drawings of standing waves  Organize observations to find a pattern  Do Now  How did closing the end of the tube change the sound? Why do you think this happened?  Agenda  Do Now  Physics Talk  Reflection  Quiz

Physics Talk 5.4  What kind of waves does sound make?  How does this relate to springs?  Compressional (longitudinal) waves

Physics Talk 5.4  What was the medium the sound traveled through?  The air in the straw or tube

Physics Talk 5.4  How do these relate to the standing waves created by the stringed instrument?  Air molecules cannot vibrate at the bottom of the test tube, so this is a node of the wave  The open end of the test tube provides the wave’s amplitude  The vibration of the air at this end, is the sound you hear  This is the antinode of the wave

Physics Talk 5.4  What is diffraction?  The ability of sound waves to spread out or change direction as they emerge from an opening  This is why you can hear someone talking around a corner  Megaphone (cheerleader thing)

Physics Talk 5.4  The top show a large amount of diffraction, when the opening is smaller  The bottom shows a small amount of diffraction, since the opening is larger

Physics Talk 5.4  How do megaphones work?  A megaphone increases the diffraction of sound, due to the small opening you yell into  The best opening size depends on the sound being produced

Vibrating Columns of Air

Physics Talk  How does changing wavelength effect frequency?  When keeping a constant wave speed, increasing the wavelength will decrease the frequency - causing a lower pitch

Physics Talk 5.4  Open tube wavelength  Closed tube wavelength  Half of the wavelength will fit  The wavelength is 2x the length of the tube  One quarter of the wavelength will fit  The wavelength is 4x the length of the tube

Physics Talk 5.4  Why does the closed straw have a lower pitch?  Why does the open straw have a higher pitch?  The wavelength is longer (4x), meaning the frequency is lower  The wavelength is shorter (2x), meaning the frequency is higher

Essential Questions pg. 525  What does it mean?  How do you know?  Why should you care?  LO and SC reflection on left side pages.