announcements 10/14/11 prayer lab 3 ends saturday a. a.see email for some more info about the...
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Announcements 10/14/11
Prayer Lab 3 ends Saturday
a. See email for some more info about the “uncertainty principle” used in the lab
Interference Path length
a. Constructiveb. Destructive
Video: Two outdoor speakers (1:16)
Ripple Tankimage: wikipedia
Reading Quiz In a standing wave, the points that have
the maximum vibration are called:a. nodesb. antinodes
Standing Waves Will occur whenever you have two waves (same
frequency, wavelength) moving in opposite directions
Math: A cos(kx - t) + A cos(kx + t) From trig.: cos(a–b) + cos(a+b) = 2cos(a)cos(b)
Can occur via refletions of a single wave! But timing (frequency) has to be just right for it to occur over & over again
Web demo, revisited http://www.colorado.edu/physics/phet/simulations/stringwave/stringWave.swf
Image by Colton
Demos Video:
http://stokes.byu.edu/standing_script_flash.html (1:48)
Demo: “Ladies belt”
Videos: Bowling ball (0:50), goblet (1:42) Youtube (on your own time): Tacoma Narrows bridge Demo: Trumpet
“Resonance”
Standing Wave Patterns Back to Ladies belt demo
a. What kinds of patterns do you get?b. “node” vs “antinode”
Harmonics
Standing waves on a string: “Closed-Closed”
For stable patterns: L = _______ What are the frequencies? Relative to the fundamental frequency?
L
L
L
L
Standing waves in air: “Open-Open”
Quick writing: draw what you think the second and third harmonics should look like
For stable patterns: L = _______ What are the frequencies? Relative to the fundamental frequency? Demo: Trumpet, again
Open end Open end
L
Example: organ pipe
Standing waves in air: “Open-Closed”
Quick writing: draw what you think the second, third, and fourth harmonics should look like
For stable patterns: L = _______ What are the frequencies? Relative to the fundamental frequency? Why wasn’t trumpet in this category?
Open end Closed end
L