fundies-ch3rev - CHAPTER 3 SOUND TRANSMISSION Sound in a...

Info iconThis preview shows pages 1–18. Sign up to view the full content.

View Full Document Right Arrow Icon
CHAPTER 3 SOUND TRANSMISSION
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Sound in a Medium Vibrating object displaces molecules in medium molecules move back and forth “bump” into others transmitting vibration thru medium
Background image of page 2
In the Medium: We have both OSCILLATION of particles and TRANSMISSION of energy (or propagation)
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Particle Motion In Air, in line with transmission-- LONGITUDINAL On Water, perpendicular to transmission-- TRANSVERSE
Background image of page 4
Displacement of Molecules in the Medium creates areas of more molecules --increased density--CONDENSATION and areas of fewer molecules --decreased density--RAREFACTION
Background image of page 5

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Because We have Transmission: We can talk about how fast sound travels in the medium = SPEED OF SOUND or c Depends on medium, temperature, density, state In Air = 344 meters/sec or 1100 feet/sec
Background image of page 6
Sound Travels Out From the Source In All Directions (at the same speed) So, Until Sound Encounters some object, the “wavefront” is spherical
Background image of page 7

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
We Can Also Talk About: Distance Traveled during each cycle = WAVELENGTH λ = c/f Wavelength = speed of sound / frequency
Background image of page 8
Wavelength Questions: What is the wavelength in meters of a 1720 Hz sound traveling in air? What is the wavelength in meters of an 86 Hz sound traveling in air?
Background image of page 9

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Question 1: Freq = 1720 cyc/sec, c = 344 m/sec wavelength = c/f =344m/sec /1720 cyc/sec =0.2 m/cyc
Background image of page 10
Question 2: Freq = 86 cyc/sec, c = 344 m/sec wavelength = c/f = 344m/sec /86 cyc/sec = 4 m/cyc
Background image of page 11

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
When Talking about Amplitude: Remember Power is Rate at which Work is done (Work /Time = Power) But the power in sound doesn’t all travel the same direction Only some of it reaches you.
Background image of page 12
Therefore, we are more interested in: How much Sound Power there is in a given area (e.g., the opening of ear canal, microphone) New term: INTENSITY = Power/Area
Background image of page 13

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Remember : Sound Power is spread over the Wavefront So the farther you are from the sound source: the larger the area over which power is spread the smaller the intensity
Background image of page 14
Intuitively, we all know this The closer you are, the louder the sound The farther away you are, the softer the sound
Background image of page 15

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
The Physics of the Situation: The relation between distance and intensity is an example of THE INVERSE SQUARE LAW Intensity = 1/distance 2
Background image of page 16
Surface area of sphere = 4 Pi r
Background image of page 17

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 18
This is the end of the preview. Sign up to access the rest of the document.