Waves: Take 2
Mr. Davis
p. 344
3,5,20,32,33,38,40,43,45
All of these terms are required for the Regents
Review: Key characteristics of waves
Amplitude: The height of the wave from node to antinode (transverse waves), or the
pressure in a compressive wave. Measured in units describing the wave
Wavelength: The distance traversed by a full cycle of the wave
Node: The “zero point” of the wave
Antinode: The extreme point of the wave (max or min amplitude)
Period: The time between successive waves
Frequency: The rate of occurrence of the wave (in Hertz or cycles / second)
The frequency
Sinusoidal Wave Form
f = 1/T
where T is the period.
0
5
10
15
20
25
Period (if axis is time)
30
35
40
How does a string make music?
•What does a string look like when vibrating?
Second Harmonic
Fundamental
First Harmonic
How do I measure
Amplitude
Wavelength
Frequency
Period
For each of these?
Videos: Superposition and wavelength
as a function of gas composition
http://www.acs.psu.edu/drussell/Demos/superposition/superposition.html
http://www.wired.com/wiredscience/2008/0
9/top-10-amazing/
Standing waves
• Two similar periodic waves traveling in
opposite directions form a standing wave.
V = nf/2L
L = l/2
What happens when two waves collide?
What happens when two waves collide?
What happens when many people in the same room talk?
What happens when an orchestra plays?
What happens when waves interact in the ocean? (The Perfect Storm)
What happens when two billiard balls collide?
What happens under the Cone of Silence?
What happens when two waves collide?
They can cancel: Superposition
(This is really addition of components of inverse sign)
Sum
What happens when two waves collide?
They can add: Superposition
Sum
What happens when two waves collide?
They pass through each other without affecting each other and keep on going
What happens when two waves collide?
They pass through each other without changing and keep on going.
(Have you ever crossed the beams of two flashlights to see what would happen?)
What happens when two waves collide?
They pass through each other without changing and keep on going.
(Have you ever crossed the beams of two flashlights to see what would happen?)
http://bestphysicsvideos.blogspot.com/2011/07/mitphysics-demo-wave-superposition.html
MIT Demonstration of Bell Labs Wave machine
Series 1
1.5
1
0.5
0
Series 1
1
-0.5
-1
-1.5
62 123 184 245 306 367 428 489 550 611 672 733 794
1.5
1
0.5
Series 1
0
1
-0.5
-1
-1.5
62 123 184 245 306 367 428 489 550 611 672 733 794
Series 2
1.5
1
0.5
Series 1
Series 2
0
1
-0.5
-1
-1.5
48 95 142 189 236 283 330 377 424 471 518 565 612 659 706 753
Series 1+2
1.5
1
0.5
0
1
-0.5
-1
-1.5
47 93 139 185 231 277 323 369 415 461 507 553 599 645 691 737 783
(
7
)
Beat Frequency
Two waves of similar frequency
Beat frequency is the difference between them
Fundamental Frequency and Harmonics
Speed of Waves
Waves have a speed!
Dependent on
•Medium
•Temperature
•Pressure
•Frequency (wavelength)
What about light?
•Medium
•Wavelength (frequency)
•(temperature)
•(pressure)
Speed of Waves
The relationship between wave speed, wavelength, and frequency is simple
•For a given temperature, pressure, material, etc.
v = fl,
where v is the speed, f is the frequency, and lambda is the wavelength.
What is v for sound?
What is v for light?
What is v for a Slinky?
Speed of Waves
Medium
Speed (m/sec)
Frequency
Sound
340
261
Light
300,000,000
Ocean Wave
25
Tsunami
260
Earthquake P
2
Earthquake
Surface
0.5
Guitar String
425
Wavelength
700E-9
1
1m
http://www.pbs.org/wgbh/nova/earth/japan-killer-quake.html
Affects on sound waves
•Vibration (tension)
•Length
•Resonance
•Affects of sound waves
•Shatter glass!
•Transmit energy!
Sugar Plum Fairy:
http://search.yahoo.com/r/_ylt=A0oG7qUs1zlPmVoAa6YPxQt.;_ylu=X3oD
MTByMTNuNTZzBHNlYwNzcgRwb3MDMgRjb2xvA2FjMgR2dGlkAw-/SIG=12095j2g1/EXP=1329219500/**http%3a//www.youtube.com/watch%
3fv=QdoTdG_VNV4
http://video.search.yahoo.com/video/play?p=sugar%20plum%20fairy%20
glasses&tnr=21&vid=1426162124191&l=207&turl=http%3A%2F%2Fts4.m
m.bing.net%2Fvideos%2Fthumbnail.aspx%3Fq%3D1426162124191%26i
d%3D4ac0756f0bc1187ac6dea26ab13b8515%26bid%3DQGXvePJox3gi
Hw%26bn%3DThumb%26url%3Dhttp%253a%252f%252fwww.youtube.co
m%252fwatch%253fv%253deQemvyyJ-g&rurl=http%3A%2F%2Fwww.youtube.com%2Fwatch%3Fv%3DeQemvy
yJ-g&sigr=11a3bvfac&newfp=1&tit=%26quot%3BDance+of+the+Sugar+Plu
m+Fairy%26quot%3B+on+the+Glass+Armonica
http://www.youtube.com/watch?v=HpovwbPGEoo
http://www.youtube.com/watch?v=wqKlCy0T-g
Wave Videos
Reflection off a sea wall:
http://www.youtube.com/watch?v=PevRZAxDxZw
Big wave at beach:
http://www.weather.com/blog/weather/8_21326.html
https://www.youtube.com/watch?v=QdoTdG_VNV4&feature
=player_embedded#at=131
Tacoma narrows bridge:
http://video.search.yahoo.com/search/video;_ylt=A2KLqIGXa
SdPEn0AIxT7w8QF?p=tacoma+narrows+bridge&b=21&tnr=20