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Physics 7C SS1Lecture 1: Waves

Dr. Emily West

ewest@physics.ucdavis.edu

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Agenda 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 http://physics.ucdavis.edu/physics7

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Clicker Setup: Joining Class

1) Turn on your clicker; it scans for classes2) If it doesn’t scan automatically, hit enter

(green button)3) Find 09SS1PHY7C; hit enter4) Display reads “ANS: 09SS1PHY7C;” hit

enter5) 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 Wave Model

Waves in 1, 2, and 3 dimensions Interference

Ray Model Reflection & Refraction Lenses

Field Model 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 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. Anything missing? xF k x=−

uur r

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Mathematics of SHMy=Displacement

A=Amplitude

T=Period

t

y

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Mathematics of SHMy=Displacement

A=Amplitude

T=Period

t

y

In this image, which numbers, if any, show… Displacement?

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4

3

5

2

6

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Mathematics of SHMy=Displacement

A=Amplitude

T=Period

t

y

In this image, which numbers, if any, show…

1

4

3

5

2

6

Amplitude?

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Mathematics of SHMy=Displacement

A=Amplitude

T=Period

t

y

In this image, which numbers, if any, show…

1

4

3

5

2

6

Period?

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Mathematics of SHM

y=Displacement

A=Amplitude

T=Period

t

y

y(t) = A sin (2 t/T)???

In this image, what is the mass doing at t=0 seconds?

A

T

T

A

Is the equation correct as is?

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Mathematics of SHM

y=Displacement

A=Amplitude

T=Period

t

y

y(t) = A sin (2 t/T + )

In this image, what is the mass doing at t=0 seconds?

In this image, what value does

have?

T

=phase

y(t) = A sin (2 t/T)?

A

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Introduction to Waves

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

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Questions to consider about waves…

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 aTIFF (Uncompressed) decompressor

are needed to see this picture.

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Definition of Wave Waves: A transfer of energy without

bringing along the mass. 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 xy(x, t) A sin ( 2 2 )

T

λ= + +

A = Amplitude, controlled by what starts the waveT = Period, how long to get back to where it started = Wavelength, repeat distance in space

T = where f is the frequency

Velocity v = f (note meters per second)

f

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