<p>20 Physical Science Properties of Waves Notes 3 Chapter 12</p><p>Demo review constructive interference then tuning fork demonstration p.339</p><p>Demo beat frequency using audacity or tuning forks (old school) refer to p. 342 for explanation (formula is not required by curriculum but the simplicity is interesting)</p><p>Example a tuning fork with a frequency of 440 hz is sounded at the same time as a piano key with a frequency of 444 Hz. What is the beat frequency ? A: 4 Hz</p><p>Modes of Vibration</p><p>Illustration tune the signal generator (hooked through the ghetto blaster) to the same pitch as a guitar string. Ask a student to turn around while you pluck the string. Can the student tell the difference? How? What distinguishes the two sound waves?</p><p>Demo standing wave with a spring. Students imagine that the spring is a large guitar string. Emphasize different modes. Summarize on the board including overtones, harmonics and the relationships between the wavelength and the frequency.</p><p>Illustration p.348 - the “sound print” idea</p><p>Demo microphone hooked through oscilloscope & compare tuning fork and guitar patterns.</p><p>Mechanical Resonance</p><p>Illustration How many people have been stuck in the snow? How do you get out? Emphasize how natural it is. Other examples: a child on a swing, dribbling a basketball truck and China my car’s rattle motorcycle (speed wobble) Hula - hoop my producing a standing wave in a spring The pendulum apparatus Resonance - the response of an object (that is free to vibrate) to a force applied with the same frequency as the natural frequency as that object.</p><p>Tacoma Narrows - film on youtube</p><p>Resonance in Air Columns</p><p>Demo wine glass then gulf tube in graduated cylinder stress that as of yet it is only called resonance because sound is being amplified</p><p>There are two types of air colunms open and closed.</p><p>I) Closed Air Columns A closed air colunm is an air column that is closed at one end and open at the other end. For a source of sound of a given frequency, resonance occurs (that is the sound is made louder) when the length of the air column (the “resonant length”, RL) is a certain length (or lengths because there can be more than one length for which resonance occurs). This length must be such that a node forms at one end and an antinode at the other. The length of a closed air column(s) is given by:</p><p>For a given resonant length, there can be several frequencies (the fundamental and overtones) that will resonate Demo - using a big graduated cylinder of a given length students can now predict what frequencies will result in resonance. Follow up with the solution on the board for those who have difficulty.</p><p>Practice p. 351 # 1 - 3 p. 367 # 47 - 51</p><p>II) Open Air Columns An open air column is an air column that is open at both ends. For a source of sound of a given frequency, resonance occurs (that is the sound is made louder) when the length of the air column (the “resonant length”, RL) is a certain length (or lengths because there can be more than one length for which resonance occurs). This length must be a multiple of half the wavelength. The length of a resonating open air column is given by:</p><p>For a given resonant length, there can be several frequencies (the fundamental and overtones) that will result in resonance. Demo using a hollow tube of a given length students can now predict what frequencies will result in resonance. Follow up with the solution on the board for those who have difficulty.</p><p>Practice p. 352 # 1 - 2 p. 367 # 52 - 57</p><p>Flight Related Topics</p><p>Lesson Mach number is the ratio of the speed of an object to the speed of sound. Recall the speed of sound depends on the temperature.</p><p>Mach (M) = speed of object note units must be the same speed of sound</p><p>Practice p. 317 (bottom) # 1,2 p. 335 #17</p><p>Demo So why is mach # important? Youtube simulation Doppler effect and then as this intereference phenomenon accounts for sound barriers and sonic booms</p><p>Doppler Effect</p><p>The apparent shift in the frequency of a sound due to the relative motion of the source</p><p>The formula is only for enrichment – not required by curriculum</p><p> f2 = f1 vs where f2 = the apparent frequency (vs + vo) f1 = the actual frequency vs = the speed of sound vo = the speed of the object Example Practice - p. 368 # 59, 58, & 60 </p>