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Sound Notes

Sound Notes. Standing Waves. A standing wave is produced when a wave that is traveling is reflected back upon itself. There are two main parts to a standing wave: Antinodes – Areas of MAXIMUM AMPLITUDE Nodes – Areas of ZERO AMPLITUDE. Sound Waves.

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Sound Notes

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  1. Sound Notes

  2. Standing Waves A standing wave is produced when a wave that is traveling is reflected back upon itself. There are two main parts to a standing wave: • Antinodes – Areas of MAXIMUM AMPLITUDE • Nodes – Areas of ZERO AMPLITUDE.

  3. Sound Waves Sound Waves are a common type of standing wave as they are caused by RESONANCE. Resonance – when a FORCED vibration matches an object’s natural frequency thus producing vibration, sound, or even damage. Example - shattering a wine glass by hitting a musical note that is on the same frequency as the natural frequency of the glass. Example – Tacoma bridge collapse

  4. Resonance Example Tacoma Narrows Bridge Collapse • http://www.youtube.com/watch?v=3mclp9QmCGs

  5. Electromagnetic vs Mechanical Waves • Electromagnetic wave - capable of transmitting its energy through a vacuum (or empty space). • Produced by the vibration of charged particles. • Ex. All light waves • Mechanical wave - not capable of transmitting its energy through a vacuum. • Require a medium in order to transport their energy from one location to another. • Ex. Sound, slinky, water, standing waves.

  6. Sound Waves • Longitudinal waves produced by a vibration • Changes in pressure (high to low) • Molecules in the air vibrate about some average position creating the compressions and rarefactions. • a wavelength is the distance from a compression to the next compression (or from a rarefaction to the next rarefaction)

  7. Frequency • Wavelength of a wave tells you the frequency • Frequency is measured in Hertz (Hz) • Frequency is the pitch of a sound • High pitch = high frequency/ Low pitch = low frequency • Doubling the frequency = octave

  8. Frequency • High frequencies are high sounds (whistle) with high pitches • Low frequencies are low sounds (tuba) with low pitches. • Who has higher frequencies, women or men?

  9. Loud Soft Loudness • Amplitude of a wave, tells you the loudness • Measure in decibels (dB) • Increase of 20 dB = twice the volume

  10. Sound Levels

  11. Loudness of Sound in Decibels

  12. Human Hearning • Below 20 Hz – Infrasonic • Elephants communication, • Average human hearing (audible sound) ranges from 20 Hz to 20,000 Hz • Above 20,000 Hz – Ultrasonic • Ultasounds

  13. Sound medium • Most sounds are transmitted through air • In general, sounds are transmitted easily in solids, then liquids, and slowest is air (gases.) • Ex. Hold your ear to the ground to hear horses off at a distance.

  14. Sound Wave Interference • Two speakers (green dots) generating sound. Listeners at the red points will hear the sound better than listeners at the blue points. • Why? Thus, constructive interference occurs wherever a thick line meets a thick line (or thin line meets a thin line) this type of interference results in antinodes (red dots). Blue dots are the nodes, places of destructive interference.

  15. Doppler Effect • phenomenon observed whenever the source of waves is moving with respect to an observer. • observed to occur with all types of waves - water waves, sound waves, and light waves.

  16. Doppler Effect • Ex. A police car traveling towards you on the highway. As the police car approached with its siren blasting, the pitch of the siren sound was high; and then suddenly after the car passed by, the pitch of the siren sound was low. 

  17. Speed of Sound • To calculate the speed of sound, use the equation: speed = distance/time s = d/t speed = frequency)(wavelength) v = fλ • Speed depends on the medium. • Will be given a chart of the various speeds in different mediums.

  18. Speed of Sound • Sound waves with a constant frequency of 250Hz are traveling through air at 0 C. What is the wavelength of the sound waves?

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