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Introduction Sound Waves outline Slide 1 Introduction slide Slide 2 Parts of a wave The wave shown is transverse but the amplitude wavelength crests and troughs apply to compressional longitudinal waves also I have a word bank on top because many students have seen this before so I make them tell me where the labels go Discuss how to measure one complete wavelength peak to peak trough to trough wherever the wave repeats one cycle Slide 3 Compressional waves vs transverse What are the differences and similarities They have the same attributes from the previous slide They are different in the direction that the amplitude vibrates perpendicular to or parallel to the direction of the moving wave What are examples of each type of wave Light is a transverse wave and sound creates compressional waves Slide 4 Frequency the number of waves passing a point in a given amount of time Demonstration Click on the waveform to see it travel to the right Have a volunteer student measure with a stopwatch as the rest of the class counts 5 complete waves go by Calculate the frequency about 1 Hz Slide 5 Students are often confused by frequency and the unit of Hertz so I use this slide to show that Hertz can measure waves per second bears per second or anything happening regularly in time Answer appears after students try to answer the question Slide 6 Using the ideas of wavelength and frequency to find the speed of a wave Explain to students that if 3 waves pass a point in one second and each wave is 2 meters long then 6 meters will pass that point Again answer appears after students try to answer Slide 7 Sound waves travel at 343 m s under normal conditions but this value can change with humidity elevation etc The key concepts are that a sound must travel through a medium like the air and b the speed of a sound wave depends on how closely the material is packed together Slide 8 To re enforce the same idea we can see a column of air where something has caused a vibration at the left end the red line is moving back and forth The sound wave travels through air until it reaches the dog s ears and the dog s brain interprets it as sound Slide 9 Must be connected to the internet and have speakers the students can hear for slides 9 and 10 Re enforcing the idea of a medium being necessary for a sound wave Click on the blank screen and a 30 second Star Wars movie clip will play Ask the students what s wrong An outside person watching shouldn t be able to here the gunfire and spaceships moving in the vacuum of outer space Slide 10 A Star Wars movie clip about 30 seconds will play in the screen Ask the students if anything seems strange about the scenes in outer space An observer shouldn t be able to hear the gunfire or spaceships fly by Slide 11 Standing waves are waves with an amplitude which is moving up and down but the wave isn t moving anywhere For example when you swing a baseball bat you create a standing wave in the bat like you see in the picture The dots are nodes the parts of a standing wave which don t move When you hit a ball with part of a bat other than the node a vibration is created in the bat which hurts your hands Instruments work on the idea of creating standing waves with air Slide 12 The wave on the top will move up and down like a guitar string to show anti nodes and nodes The equation shows that if you change the guitar string length the frequency will change If you change the density of the string which changes the velocity you will also change the frequency of the string The bottom pictures show that a tube with two open ends can only have multiples on wavelengths inside while a tube with one closed end can have multiples of wavelengths Slide 13 Some sound examples of the three types of instruments we talk about string percussion and woodwind For each of them vibrations created in the instrument cause vibrations in the air which travel to the listener s ear Slide 14 The Doppler Effect occurs when an observer hears the frequency of sound waves in front of and behind a passing object like a fire engine Slide 15 The stages of an object breaking the sound barrier 1 a sound source standing still like a jet sitting on the runway before take off 2 An object which is moving but at a speed smaller than the speed of sound 3 An object travels at the speed of sound so the sound waves produced in front of the object cannot move away from it Slide 16 This is a really interesting video found at the website noted The weather conditions had to be correct for this to happen The water vapor in the air can be seen as the gathering wall of sound waves pressurizes it into a visible form As the jet passes the ship you can see the cone of the sound waves starting at the point of the jet I don t know if the jet it quite traveling the speed of sound since the video is 9 seconds long at the jet would have to travel about 3100 meters almost 2 miles in that time to be going the speed of sound Slide 17 A few of the things to discuss when mentioning that waves carry energy earthquakes tsunamis and tidal waves Earthquakes and tsunamis are both created by the movement of techtonic plates The water waves produced tsunami is Japanese for harbor wave can be as tall as 100 feet and travel half the speed of sound Tidal waves are different and are created from the energy of high winds A good quick demonstration is just to stick a vibrating tuning fork into a glass of water The water will splash everywhere showing the point that energy is transferred the tuning fork to moving water Slide 18 One of the labs we worked on with the students involved resonance It can be a difficult thing to understand so the key point is that they understand that a solid object has a natural frequency it likes to vibrate at


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