Welcome to Physics 7C

Emily Ashbaugh

eashbaugh@physics.ucdavis.edu

Some Logistics

Course Webpage: http://physics.ucdavis.edu/physics7

Simple Harmonic Oscillation Review

How can we describe the motion of oscillating objects?

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

Mathematics of SHM

y=Displacement

A=Amplitude

T=Period

t

y

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

1

4

3

5

2

6

Amplitude?

Period?

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?

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

Making Waves

Watch waves How does the motion you are

watching differ from the motion of the mass-spring?

How is it the same? What new constructs are

needed to describe waves? What constructs can I control

when I start the wave? What moves from one end of the

machine to the other?

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

Wave Constructs

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.

Graphing Wavesa) At a particular time (holding position constant)

b) At a particular position (holding time constant)

Mathematics of Harmonic Waves

Displacement (y) is a function of both position along the medium and time. y(x,t)

In space, function repeats every wavelength In time, function repeats every period

t xy(x, t) A sin ( 2 2 )

T

λ= + +

Longitudinal vs. Transverse Wave Polarization

Longitudinal Wave Transverse Wave

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