1. Compressional Waves

2.  Requires a medium for propagation.  Compression of molecules transmit sound.

3.  Compression - molecules of medium are crowded together by energy.  Rarefaction - molecules of medium are far apart.

5. - 1 compression + 1 rarefaction - Compression to compression - Rarefaction to rarefaction

7.  Number of Compressional waves that pass a point in 1 s.  v = f λ |v = d/t  v = velocity|velocity = distance  f = frequencytime  λ = wave length

8.  Amount of compression  Increase in energy increases compression High Amplitude Low Amplitude

9. Depends on :  Medium (Ex. air, water)  Wave travels faster in more dense media.  Temperature of the medium  Slower in cold air than warm air.  Warm molecules move faster than cold molecules.

10.  1 million times faster than sound  Ex. Lightning  See lightning before you hear thunder

11.  At 0° C = 332 m/s V air = 332m/s + ( o C x 0.6 m/s)  Find speed of sound in air at 20° C V air = 332 m/s + (20 o C x 0.6 m/s) = 344m/s

12.  At 10° C lightning strikes and 8 s later you hear thunder. How close is the lightning to you ? Distance = time x speed of sound d = t x v (at 10° C) d = t x v (at 10° C) d = (8 s) x 332 m/s + (10° C x 0.6m/s) d = (8 s) x 332 m/s + (10° C x 0.6m/s) d = 2704 m d = 2704 m

13.  At 0° C = 1454 m/s V water = 1454 m/s + o C (2.3 m/s)  Find speed of sound in water at 20 o C. V water = 1454 m/s + (20 o C x 2.3 m/s) = 1500 m/s

14.  A ship’s sonar pings the bottom of the ocean whose temperature is 30° C. The sound travels down and back in 3.8 s. d = t x v (at 30° C ) d = t x v (at 30° C ) d = (3.8 s) x 1454 m/s + (30° C x 2.3m/s) = 2762.6 m d = (3.8 s) x 1454 m/s + (30° C x 2.3m/s) = 2762.6 m 2

16.  The "highness" or "lowness" of a sound.  Depends on frequency.  Higher Frequency = Higher Pitch  Sound causing glass to resonate Sound causing glass to resonate

17.  A Human ear can hear sound frequencies between 20 Hz and 20,000 Hz

19.  Ultrasonic waves - > 20,000 Hz (heard by bats and dogs)  Infrasonic waves - less than 20 Hz

20.  Used by humans for imaging purposes  Used by many animals for echolocation (sensing space and surroundings through sound)  Porpoises can here up to 160,000 Hz

21.  Can be generated by earthquakes, volcanoes, aurorae, meteors, oceans, and upper atmosphere lightning.  Used by whales to communicate over hundreds of miles.  Can cause unsettling feelings in humans.

22.  Intensity - depends on amount of energy in wave. This is the sound's amplitude.  Measured in decibels (dB)

23. Threshold of Hearing 0 dB Rustling Leaves 10 dB Whisper 20 dB Normal Conversation 60 dB Busy Street Traffic 70 dB Large Orchestra 98 dB CD Player Max Vol 100 dB Vacuum Cleaner 107 dB Front Rows of Rock Concert 110 dB Threshold of Pain 130 dB Military Jet Takeoff 140 dB Instant Perforation of Eardrum 160 dB

24.  Any sound > 120 dB may cause pain and permanent hearing loss.  As you age you cannot hear sounds of higher frequencies.

25.  As an object producing a wave (ie. sound) approaches an observer the waves become compact, increasing the frequency. As the object leaves the waves spread out  doppler effect how it works doppler effect how it works  Doppler effect train Doppler effect train

26.  supersonic car supersonic car  A sonic boom is heard when an object enters supersonic speeds.

27.  Longitudinal waves – compression rarefaction  Transverse Wave – up and down motion

29.  Ocean waves and vibrating strings produce transverse waves.  Sound and produce longitudinal waves (compression waves)  Earthquakes produce both (S waves and P waves)

30.  Cycle = 1 crest + 1 trough or 1 compression + 1 rarefaction  Frequency (f) = cycles/second  Measured in Hertz (Hz)  Period (T) = seconds/cycle

31.  standing wave in water standing wave in water

32.  Mechanical waves, such as sound and ocean waves require a medium.  Electromagnetic waves, such as light do not.

33.  Reflection : when a wave bounces off of an object (ie. light off a mirror, an echo.)  Refraction : when a wave bends as it moves from one medium to another (ie. the illusion of a bent straw in water.)  Diffraction : when a wave bends around the edge of an of an object or through a slit.

34.  Interference is when waves from two different sources run into each other.  Destructive interference is when the trough of one wave matches the crest of another. The two waves cancel each other out.  Constructive interference is when the crest of one wave overlaps the crest of another and the two waves add together increasing their amplitude.