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December 16, 2015 What is the difference between a compression and rarefaction? What type of waves have these?
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Today Check: HW Part 1-6 Notes: Doppler Effect
Assignment: Start Part 7 Homework: Finish part 7
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Q: What is the Doppler Effect?
When a sound travels toward you and then away from you the change in sound is called the Doppler Effect Ex. Ambulance passing you: high pitch when traveling toward you, then low pitch when traveling away.
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Q: What is the Doppler Effect?
Due to a perceived change in frequency (notice the number of waves hasn’t changed, but they are just squished into a smaller area)
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Q: What causes a sonic boom?
When an object is traveling at the speed of sound, the waves in the front of the object become all bunched up. Then, the object travels faster than the speed of sound. (Supersonic!)
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Q: What causes a sonic boom?
This bunching causes a shock wave
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Q: What causes a sonic boom?
The audio result is a sonic boom- when all the compressions and rarefactions are heard at one time
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Q: What happens when two waves collide?
This means two waves are traveling toward each other. Called interference
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2 Types of Interference: Type 1
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2 Types of Interference: Type 1
Constructive Interference Colliding waves cause an increase in amplitude, which means a louder sound Both waves are at crests (or in compression) OR at troughs (or in rarefaction)
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2 Types of Interference: Type 2
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2 Types of Interference: Type 2
Destructive Interference Colliding waves cause a decrease in amplitude, which means a quieter sound (maybe completely cancel out) One wave is a crest and other is a trough (or one is in compression, the other is in rarefaction)
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AFTER INTERFERENCE OCCURS….
Waves continue on as if nothing happened (they don’t stop!)
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Why does this matter? Interference is the cause of “beats” when two sounds collide.
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PRACTICE PROBLEM For each point (G – O), identify if destructive or constructive interference is occuring.
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Wave Interactions Reflection Refraction Diffraction
Wave hits something and bounces back Causes echoes of sound Refraction Wave changes speed and bends due to change in medium Ex. Looking at a glass of water with a straw that looks bent/broken, depth perception in lakes, pools, etc Diffraction Wave travels around barriers (ex. Out the door and down the hall)
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