Transcript Physics 7C SS1 Lecture 1: Waves

Physics 7C SS1
Lecture 1: Waves
Dr. Emily West
[email protected]
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Agenda
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Logistics: Syllabus and Web Page
Clicker Setup
Course Overview--the models of 7C
Simple Harmonic Motion Review
Wave Introduction
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Course webpage
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http://physics.ucdavis.edu/physics7
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Clicker Setup: Joining Class
1) Turn on your clicker; it scans for classes
2) If it doesn’t scan automatically, hit enter
(green button)
3) Find 09SS1PHY7C; hit enter
4) Display reads “ANS: 09SS1PHY7C;” hit
enter
5) When you’ve successfully joined, display
reads “ANS: wait for Q”
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Clicker Setup: Student ID
1) Turn on your clicker
2) Press * to access Setup Menu
3) Scroll to find “ID;” hit Enter (green
button)
4) Enter your Student ID so I can give
you credit; hit enter
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Check Clicker Setup
When did you take 7B?
a) Spring 09
b) Winter 09
c) Fall 09 or earlier
d) Didn’t take 7B (but took 7A)
e) I haven’t taken any 7-series classes
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Course Overview:
Models of 7C
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Wave Model
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Ray Model
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Waves in 1, 2, and 3 dimensions
Interference
Reflection & Refraction
Lenses
Field Model
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Electricity
Magnetism
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Simple Harmonic Motion Review
How can we describe the motion of oscillating objects?
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Simple Harmonic Motion
(SHM) Constructs
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Amplitude: maximum distance from equilibrium
Period (or frequency): amount of time required to
complete a cycle (or number of cycles per unit time)
Equilibrium: position at which all forces acting on the
object sum to zero.
Displacement: position of the object relative to
equilibrium
Restoring Force: a force that acts on an object that
tends move it toward equilibrium
Defining SHM: The restoring force is proportional to
the displacement.
Fx  k x
Anything missing?
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Mathematics of SHM
y
y=Displacement
A=Amplitude
T=Period
t
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Mathematics of SHM
y
y=Displacement
A=Amplitude
T=Period
1
6
4
t
2
3
In this image, which
numbers, if any,
show…
Displacement?
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Mathematics of SHM
y
y=Displacement
A=Amplitude
T=Period
1
6
4
t
2
3
5
In this image, which
numbers, if any,
show…
Amplitude?
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Mathematics of SHM
y
y=Displacement
A=Amplitude
T=Period
1
6
4
t
2
3
5
In this image, which
numbers, if any,
show…
Period?
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Mathematics of SHM
y
y=Displacement
A=Amplitude
T=Period
A
t
A
T
T
In this image, what
is the mass doing at
t=0 seconds?
Is the equation
correct as is?
y(t) = A sin (2p t/T)???
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y
Mathematics of SHM
y=Displacement
A=Amplitude
T=Period
T
f=phase
t
A
In this image, what
is the mass doing at
t=0 seconds?
In this image, what
value does f have?
y(t) = A sin (2p t/T)?
t/T + f)
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Introduction to Waves
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
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Questions to consider about
waves…
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What new constructs are needed
to describe waves?
What constructs can I control
when I start the wave?
What constructs are set by the
medium that carries the wave?
What moves from one end of the
machine to the other?
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
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Definition of Wave
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Waves: A transfer of energy without
bringing along the mass.
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Particles in the medium get disturbed and
collide, but they stay oscillating about one
position; they don’t travel with the wave.
The medium does not effectively move.
The disturbance advances, that’s the wave.
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A vibrating object acts as the source of the wave. As a speaker
moves through a cycle, it fixes the period and frequency.
t
x
y(x, t)  A sin ( 2p
 2p
 )
T

A = Amplitude, controlled by what starts the wave
T = Period, how long to get back to where it started
 = Wavelength, repeat distance in space
T=
1
f
where f is the frequency
Velocity v =  f
(note meters per second)
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