Periodic Wave A wave whose displacement has a

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Periodic Wave • A wave whose displacement has a periodic variation with time or

Periodic Wave • A wave whose displacement has a periodic variation with time or distance, or both.

Types of Waves • Electromagnetic: • Transverse: • Longitudinal:

Types of Waves • Electromagnetic: • Transverse: • Longitudinal:

Speed of Sound and Light • Speed of Sound in air – 331 m/s

Speed of Sound and Light • Speed of Sound in air – 331 m/s • Speed of Light in a vacuum – 3. 0*10^8 m/s

How do we easily represent waves that move outward from a source?

How do we easily represent waves that move outward from a source?

http: //paws. kettering. edu/~drussell/Demos/waves/ wavemotion. html compression

http: //paws. kettering. edu/~drussell/Demos/waves/ wavemotion. html compression

What type of wave is a Sound wave?

What type of wave is a Sound wave?

Pitch • Pitch is related mainly to the frequency of the sound • Pitch

Pitch • Pitch is related mainly to the frequency of the sound • Pitch is not a physical property of the sound • Frequency is the stimulus and pitch is the response – It is a psychological reaction that allows humans to place the sound on a scale – Frequencies are exact, pitch can differ due to our human perception

Human hearing ranges

Human hearing ranges

Pitch is the perception of frequency. <20 Hz = infrasonic 20 -20000 Hz =

Pitch is the perception of frequency. <20 Hz = infrasonic 20 -20000 Hz = audible >20000 Hz = ultrasonic

Animal Hearing Ranges • Humans hear “audible” sounds • Elephants can hear “subsonic” aka

Animal Hearing Ranges • Humans hear “audible” sounds • Elephants can hear “subsonic” aka “infrasonic” waves (14 -12, 000 Hz) http: //www. rambles. net/payne_interview. html • Dogs can hear “supersonic” (67 -45, 000 Hz) http: //www. lsu. edu/deafness/Hearing. Range. html Test your own hearing range! http: //www. noiseaddicts. com/2009/03/can-youhear-this-hearing-test/

Intensity Level of Sound Waves • The louder the wave, the bigger the amplitude

Intensity Level of Sound Waves • The louder the wave, the bigger the amplitude of the wave. Loudness is measured in decibels (d. B) or Watts per meter squared(W/m 2).

Sound Intensity • Try your hearing range at: • http: //www. phys. unsw. edu.

Sound Intensity • Try your hearing range at: • http: //www. phys. unsw. edu. au/jw/hearing. html

Speed of Sound in Air • 331 m/s is the speed of sound at

Speed of Sound in Air • 331 m/s is the speed of sound at 0° C • T is the absolute temperature

When an object makes a sound, the sound waves propogate out in all directions.

When an object makes a sound, the sound waves propogate out in all directions. Assuming the object is stationary.

But what if that object is moving?

But what if that object is moving?

 • The apparent change in frequency of a wave caused by relative motion

• The apparent change in frequency of a wave caused by relative motion between the source of the wave and the observer. https: //www. youtube. com/watch? v=z 0 Eaoilzg. GE

Doppler Effect- Doppler Shift https: //www. youtube. com/watch? v=h 4 On. BYrb. Cj. Y

Doppler Effect- Doppler Shift https: //www. youtube. com/watch? v=h 4 On. BYrb. Cj. Y

Ultrasonic Sound • The term "ultrasonic" applied to sound refers to anything above the

Ultrasonic Sound • The term "ultrasonic" applied to sound refers to anything above the frequencies of audible sound, and nominally includes anything over 20, 000 Hz. Frequencies used for medical diagnostic ultrasound scans extend to 10 MHz and beyond.

Shock Waves, final • Shock waves carry energy concentrated on the surface of the

Shock Waves, final • Shock waves carry energy concentrated on the surface of the cone, with correspondingly great pressure variations • A jet produces a shock wave seen as a fog Video Clip http: //www. metacafe. com/watch/1956849/sonic_boom/

Forced Vibrations • A system with a driving force will force a vibration at

Forced Vibrations • A system with a driving force will force a vibration at its frequency • When the frequency of the driving force equals the natural frequency of the system, the system is said to be in resonance

Examples of Resonance • Child being pushed on a swing • Shattering glasses •

Examples of Resonance • Child being pushed on a swing • Shattering glasses • Tacoma Narrows Bridge collapse due to oscillations by the wind • Upper deck of the Nimitz Freeway collapse due to the Loma Prieta earthquake

When something vibrates at its natural frequency, you get resonance! http: //video. google. com/videoplay?

When something vibrates at its natural frequency, you get resonance! http: //video. google. com/videoplay? docid=3932185696812733207&ei=y. A 2 RS 9 Lc. Ipf. Cr. ALEr 5 y_Ag&q=tacoma+narrows+bridge&hl=e

Standing Waves • When a traveling wave reflects back on itself, it creates traveling

Standing Waves • When a traveling wave reflects back on itself, it creates traveling waves in both directions • The wave and its reflection interfere according to the superposition principle • With exactly the right frequency, the wave will appear to stand still – This is called a standing wave

Harmonics • when an object is forced into resonance vibrations at one of its

Harmonics • when an object is forced into resonance vibrations at one of its natural frequencies, it vibrates in a manner such that a standing wave pattern is formed within the object. These forced vibrations in an object are only created within the object or instrument at specific frequencies of vibration; these frequencies are known as harmonic frequencies, or merely harmonics.

Harmonics explained

Harmonics explained

For your instrument project….

For your instrument project….

Beats • Beats are alternations in loudness, due to interference • Waves have slightly

Beats • Beats are alternations in loudness, due to interference • Waves have slightly different frequencies and the time between constructive and destructive interference alternates • The beat frequency equals the difference in frequency between the two sources:

Quality of Sound – Tuning Fork • Tuning fork produces only the fundamental frequency

Quality of Sound – Tuning Fork • Tuning fork produces only the fundamental frequency

Quality of Sound – Flute • The same note played on a flute sounds

Quality of Sound – Flute • The same note played on a flute sounds differently • The second harmonic is very strong • The fourth harmonic is close in strength to the first