Lecture 35. Results from Exam #3 Overall Grades Thus Far Sketch of Remainder of the Semester Chapter 13: Hooke’s Law (again!) Simple Harmonic Motion. Monday, November 30, 1998. Physics 111. Exam 3. Generally, most of you did WAY better this time!.
Results from Exam #3
Overall Grades Thus Far
Sketch of Remainder of the Semester
Chapter 13: Hooke’s Law (again!)
Simple Harmonic Motion
Monday, November 30, 1998
Generally, most of
you did WAY
better this time!
I guess it really was a pretty EASY test…
As you’ll be able to tell from the grade
distribution which sits about 14 points
higher than either of the two previous
You should have been able to really
ENJOY your turkey dinner!
If I had to
(As seen on the Physics 111 web site…)
I have compiled overall grades up through
and including Exam #3. I have dropped your
lowest homework grade (as promised) but
have NOT dropped your lowest exam score(yet). I will do the latter at the end of the
semester. You will find your current overall
average marked on your test in purple crayon.
If your average
is below 70, you
might like to stop
by and visit me.
Please, do not leave town early…you’ll
just make my life …ahem…
Our final exam period is scheduled for the
very last possible day of finals’ week:
Friday, December 18, 1998!
(Is that pathetic enough?)
This 2-hour exam period will contain TWO exams.
The first 50 minutes will be used for an exam
on the material that we cover over the next two
weeks. It will be structured very much like
Exam #3 (three sections, one of which will be
multiple choice---you do two of the three). You
will be permitted to use the usual 3”X5” note
1 hour plus
5 sections, you do 4 (one will be multiple choice)
Each section somewhat shorter (25 points)]
8.5”X11” crib sheet + 3”X5” notecard from
I will give you math & constants but not
Exam #4 (during the first 50 minutes of our
final exam period) counts the same as the
previous 3 exams (the best 3 scores from
Exams #1 - 4 count 15% each).
If you are REALLY happy with your performance
on the first 3 exams, simply notify me and you
will be permitted to SKIP Exam #4. In this case
you may show up 50 minutes into the exam
(I’m guessing there won’t be too many of YOU!)
Everyone MUST take the Final Exam.
You cannot pass this class without completing the final exam.
The final exam counts for everyone and
is worth 20% of your final grade.
There will be TWO more
- due Monday, December 7
- due Friday, December 11
There will be two more meetings of Lab:
- Thursday, December 3 (Lab 10)
- Thursday, December 10 (Lab Final=Party?)
We are going to skip Chapter 12 -- not that the
material in Chapter 12 isn’t important, but I think
the time is better spent on waves and sound
(Chapters 13 and 14).
Vibrations and Waves
We’ve already studies some vibrational motion,
when we we examining the curious behavior
of springs and objects that interact with them.
We will expand our studies to objects that
behave similarly to our spring, such as the
pendulum and rotating objects.
We’re going to start by reviewing some
of the basic properties of springs.
You may recognize this stuff…These are
the same notes I used back in Chapter 5!
So let’s go through them quickly just
to refresh our memories -- especially
after that long Thanksgiving Break!
However, if we compress or stretch the spring
by some amount x, then the spring is observed
to exert a Force in the opposite direction.
Hook discovered this force could be modeled
by the mathematical expression
F = - kx
Notice that this force operates along a linear line!
Slope of this line
is -k, where k is
the spring constant.
Which means that if we looked at the plot
of Force versus compression/stretching x...
Notice that the force is always in the
OPPOSITE direction of the displacement.
We call such a force a
Because the force acts
to “restore” the particle
to its original position.
If we look at the work done by an applied
force which compresses the spring through
a distance (-x1)...
Work done BY the
external force ON
This energy is stored in the spring...
Potential Energy of a spring is
So, for spring problems, we have a new
TOTAL MECHANICAL ENERGY given by
And it is THIS quantity which will be conserved
absent other, outside forces.
Springs & Energy
A wealthy socialite,
bored of counting
his gold coins, decides
to play with his new
Predict the motion
of the mass at the
bottom of this
spring as explicitly
Assume no friction and
no air resistance.
Now, sketch a plot
of the height of the
block above the floor
as a function of time.
What kind of
familiar) result in
such a pattern?
This type of oscillatory behavior is known as
Simple Harmonic Motion
An object in simple harmonic motion displays
an acceleration that is proportional to the
displacement and in the opposite direction.