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NIS – PHYSICAL SCIENCE. Lecture 44 – Lecture 45 Sound Ozgur Unal. Sound Waves. When an object vibrates, it creates sound waves. Remember that sound waves are compressional waves.
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NIS – PHYSICAL SCIENCE Lecture 44 – Lecture 45 Sound OzgurUnal
Sound Waves • When an object vibrates, it • creates sound waves. • Remember that sound waves • are compressional waves. • When an end of the tuning fork moves outward, it forms a compression on that side by pushing the molecules in air together. • When the end of the tuning fork moves back, a rarefaction is formed where the molecules are farther apart. • As the tuning fork vibrates, it produces a series of compressions and rarefactions that travel outward.
Speed of Sound • Sound waves can travel in any material whether gas, liquid or solid. • Sound cannot travel in empty space. • The speed of sound depends on the medium Table 1 • In general, sound travels slowest in gases and fastest in solids. Why? • http://www.ndt-ed.org/ • EducationResources/HighSchool/ • Sound/speedinmaterials.htm • As the temperature increases, the • speed of sound also increases. Why? • Example: The speed of sound at 0 oC is 331. m/s, but when the temperature is 20 oC , the speed increases to 343 m/s.
Amplitude and Energy of Sound Waves • How do we determine the amplitude of a compressional wave? • How is amplitude related to the energy carried by the wave?
Intensity and Loudness • http://www.youtube.com/watch?v=nTI2FdoeMlc&feature=fvst • If you move away from the speaker, how does the sound change? • As you move away from the sound source, the energy carried by the wave spreads over a larger area. • The amount of energy transferred by a sound wave through a certain area each second is the intensity of the sound wave. • Intensity decreases as you move • away from a sound source. • This means that, as you get farther • away from the source, less energy • reaches yoru ears each second.
Intensity and Loudness • Loudness is the human perception of sound intensity. • As the intensity of a sound wave increases, the loudness of the sound also increases. • The intensity of sound (loudness) can be described using a measurement scale. • Each unit on the scale is called a • decibel, dB. • On this scale the faintest sound • that most people can hear is 0 dB. • Sounds with intensity levels • above 120 dB may cause pain and • permanent hearing loss.
Intensity and Loudness • How can you protect your ears from sound with high dB? • Using ear plugs and ear muffs can help you protect your ears.
Pitch and Frequency • Are you familiar with the musical notes? • http://ababasoft.com/music/music01.html • Pitch is the human perception of the frequency of sound waves. • Pitch gets higher as the • frequency of the sound • waves increases. • The frequency (pitch) • of each musical note is • different from one another. • Check out Figure 5.
Pitch and Frequency • A healthy human ear can hear sound waves with frequencies from about 20 Hz to 20,000 Hz. • The human ear is most • sensitive to sounds in the • range of 440 Hz to about • 7,000 Hz. • Sound waves above 20,000 Hz are called ultrasonic waves. • Dogs can hear sounds with frequencies up tp 35,000 Hz. • Bats can detect frequencies higher than 100,000 Hz. • Infrasonic, or subsonic, waves have frequencies below 20 Hz. • Although you can’t hear infrasonic waves, you might feel them as a rumble inside your body.
The Doppler Effect • Watch the video in the link, and describe how the sound from the car changes as it passes by. • http://www.wfu.edu/physics/demolabs/demos/3/3b/3B40xx.html • As the car approaches, the pitch of the sound increases. • As the car goes away, the pitch decreases. • This change in pitch or frequency due to relative motion of a wave is called the Doppler effect. • Have a look at the animation below: • http://galileoandeinstein.physics.virginia.edu/more_stuff/flashlets/doppler.htm
The Doppler Effect • The Doppler effect happens any time the source of a sound is changing position relative to the listener. • It occurs no matter whether it is • the sound source or the listener • that is moving.
Using Sound • When sound waves strike an object, they • can be absorbed by the object, transmitted through the object, or reflected from the object. • By detecting the sound waves reflected from an object, the size, shape and location of an object can be determined. • Applications of sound waves: • Echolocation and Sonar: Echolocation is the process of locating objects by emitting sounds • and detecting the sound waves that • reflect back. • Example: Bats, dolphins and whales • Sonar is a system that uses the • reflection of underwater sound • waves to detect objects.
Using Sound • Ultrasound in Medicine: • Using special instruments, medical professionals can send ultrasonic waves into a specific part of a patient’s body. • Examples: • Monitoring the development of fetus • Monitoring certain types of heart disease and cancer • Breaking kidner stones and gallstones