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Edit Comment Close Premium member Presentation Transcript Slide 1: Sound Longitudinal wave requires a medium (cannot travel in a vacuum) Slide 2: is known as ACOUSTICS Study of Sound Slide 3: Properties of Sound A sound is a vibration The vibrating causes the air molecules near the movement to be forced closer. This is called compression As the vibration moves on, the density and air pressure becomes lower than normal and is called rarefaction Pressure wave – longitudinal Frequency = pitch v = 334 m/s in air at room temperature Velocity is dependent upon the material Slide 4: Do molecules move faster or slower as temperature increases? So would sound travel faster or slower as temperature increases? Temperature Can affect speed Slide 5: Waves travel fastest in solids, slowest in gases. Solid Liquid Gas Type of Medium Slide 6: Speed of sound Fastest in solids, slowest in gases. Air = 340 m/s water= 1440 m/s steel = 5000 m/s Supersonic: faster than the speed of sound. Slide 7: Sound travels faster in warm water than in cold water By measuring the time it takes for sound to travel a known distance through the ocean the average temperature of the water can be calculated = ATOC (acoustic thermometry of ocean climate) Speed of sound Speeds of Soundat T = 20 C : Speeds of Soundat T = 20 C Air Helium Hydrogen Water Sea water Iron/Steel Glass Aluminum 343 m/s 1005 m/s 1300 m/s 1440 m/s 1560 m/s ≈5000 m/s ≈ 4500 m/s ≈ 5100 m/s Slide 9: The highness or lowness of sound. Depends on the frequency of sound waves. High frequency = High pitch Low frequency = Low pitch Pitch Slide 10: Also called LOUDNESS Amount of energy Depends on the amplitude of sound waves. (amplifier) Large Amp. = Loud sound Small Amp. = Soft sound Intensity Intensity of Sound : Intensity of Sound Unit is the “Bel”. Named after Alexander Graham Bell More commonly used is the decibel (dB) = 0.1 Bel (in dB) = 10 log(I/I0) I is the intensity ( A2) I0 = 1.0 x 10 -10 W/m2 the “threshold of hearing” Some Intensities (in dB) : Some Intensities (in dB) Jet plane at 30 m Threshold of pain Indoor rock concert Auto interior Street traffic Conversation Whisper Rustle of leaves 140 120 120 75 70 65 1x10-10 1x10-11 Slide 13: Sound waves reflecting from hard surfaces Ex.: Multiple echo resulting from the direct sound AND the reflected sound Reverberation Reverberation vs Echo : Reverberation vs Echo Animations courtesy of Paul Hewitt and borrowed from physicsclassroom.com Slide 15: Near total silence - 0 dB A whisper - 15 dB Normal conversation - 60 dB Lawnmower - 90 dB Threshold of pain - 120 dB A rock concert or a jet engine - 120 dB Gunshot, firecracker - 140 dB Measurement of loudness Decibels Sound is a pressure wave : Sound is a pressure wave Animations courtesy of Paul Hewitt and borrowed from physicsclassroom.com Ear : Ear Slide 18: Human Ear 20Hz--20 000 Hz Infrasonic: below 20 Hz (below our hearing) Ultrasonic Sound: above 20,000Hz (above our hearing) Tuning fork creating a sound wave : Tuning fork creating a sound wave Animations courtesy of Paul Hewitt and borrowed from physicsclassroom.com Ultrasounds : Ultrasounds Ultrasound can be used to create internal images of the human body Ex. Pregnant woman gets a “picture” of her unborn baby Slide 21: An equal mixture of all frequencies of sound Used to calm stress Used in office buildings White Noise Slide 22: Yep! There is such a thing Causes: Damage to ear resulting in hearing loss Stress Noise Pollution Slide 23: Caused by destructive interference Result – hardly any or no sound Bad for concert halls – designers be careful! Dead Spots Slide 24: Used to locate underwater objects and distances. ***Reflection** sonar Doppler Effect : Doppler Effect Apparent change in frequency (pitch) of a sound from a moving source. Source moving toward observer: f’ = f / (1-vs/v) Source moving away from observer: f’ = f / (1+vs/v) f = frequency of source, f’=frequency heard by observer, vs = velocity of source, v = velocity of sound Slide 26: Change in pitch due to motion. Doppler effect Slide 29: *Moving towards increases the pitch *Moving away decreases the pitch *Think of sirens Doppler effect zoom Guitar String creating a sound wave : Guitar String creating a sound wave Animations courtesy of Paul Hewitt and borrowed from physicsclassroom.com You do not have the permission to view this presentation. In order to view it, please contact the author of the presentation.