Waves

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

Types of Waves Electromagnetic: Transverse: Longitudinal:

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?

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

What type of wave is a Sound wave?

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

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 “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/HearingRange.html Test your own hearing range! http://www.noiseaddicts.com/2009/03/can-you- hear-this-hearing-test/

Intensity Level of Sound Waves The louder the wave, the bigger the amplitude of the wave. Loudness is measured in decibels (dB) or Watts per meter squared(W/m2).

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 0° C T is the absolute temperature

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?

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=z0EaoilzgGE

Doppler Effect- Doppler Shift https://www.youtube.com/watch?v=h4OnBYrbCjY

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 Video Clip 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 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 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?docid=-3932185696812733207&ei=yA2RS9LcIpfCrALEr5y_Ag&q=tacoma+narrows+bridge&hl=en#

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 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

For your instrument project….

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 – 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