fundies-ch3rev

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

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

CHAPTER 3 SOUND TRANSMISSION

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

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

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

View Full Document
Particle Motion In Air, in line with transmission-- LONGITUDINAL On Water, perpendicular to transmission-- TRANSVERSE
Displacement of Molecules in the Medium creates areas of more molecules --increased density--CONDENSATION and areas of fewer molecules --decreased density--RAREFACTION

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

View Full Document
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
Sound Travels Out From the Source In All Directions (at the same speed) So, Until Sound Encounters some object, the “wavefront” is spherical

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

View Full Document
We Can Also Talk About: Distance Traveled during each cycle = WAVELENGTH λ = c/f Wavelength = speed of sound / frequency
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?

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

View Full Document
Question 1: Freq = 1720 cyc/sec, c = 344 m/sec wavelength = c/f =344m/sec /1720 cyc/sec =0.2 m/cyc
Question 2: Freq = 86 cyc/sec, c = 344 m/sec wavelength = c/f = 344m/sec /86 cyc/sec = 4 m/cyc

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

View Full Document
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.
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

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

View Full Document
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
Intuitively, we all know this The closer you are, the louder the sound The farther away you are, the softer the sound

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

View Full Document
The Physics of the Situation: The relation between distance and intensity is an example of THE INVERSE SQUARE LAW Intensity = 1/distance 2
Surface area of sphere = 4 Pi r

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

View Full Document
This is the end of the preview. Sign up to access the rest of the document.