sound notes
DESCRIPTION
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. - PowerPoint PPT PresentationTRANSCRIPT
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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.
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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
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Tacoma Narrows Bridge Collapse
http://www.youtube.com/watch?v=3mclp9QmCGs
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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.
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• 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)
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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
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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?
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Amplitude of a wave, tells you the loudness
Measure in decibels (dB) Increase of 20 dB = twice the volume
Loud Soft
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Sound Loudness (dbs) Hearing Damage
Average Home 40-50
Loud Music 90-100 After long exposure
Rock Concert 115-120 Progressive
Jet Engine 120-170 Pain
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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
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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.
Speed of Sound in Various Media
Medium Speed of Sound (m/s)
Air (0°C) 331
Air (20°C) 343
Helium (0°C) 972
Water (25°C) 1493
Seawater (25°C) 1533
Copper (25°C) 3560
Iron (25°C) 5130
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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.
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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.
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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.
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To calculate the speed of sound, use the equation:speed = distance/time s = d/tspeed = frequency)(wavelength) v = fλ
Speed depends on the medium. Will be given a chart of the various speeds
in different mediums.
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Sound waves with a constant frequency of 250Hz are traveling through air at 0 C. What is the wavelength of the sound waves?
Speed of Sound in Various Media
Medium Speed of Sound (m/s)
Air (0°C) 331
Air (20°C) 343
Helium (0°C) 972
Water (25°C) 1493
Seawater (25°C) 1533
Copper (25°C) 3560
Iron (25°C) 5130