Physics 218: Mechanics

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Physics 218 Mechanics
Instructor Dr. Tatiana Erukhimova
Lectures 38-39
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Test 3
Number of students
90
30
60
80
70
50
Score
Average 63 High 100 Low 1
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Physics 218 Challenge Exam will take place on
December 1. Please come and participate!
DATE  Monday, December 1, 2008TIME  600
p.m.LOCATION  202T ENPH
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To All Physics 218 Students in All Sections We
are pleased to announce the fall 2008 competition
for the Award for Exceptional Performance in
Physics 218. As many of you know, every semester
there is a challenge exam given at the end of the
semester to determine these awards. This exam is
open to all students in all sections. It will
cover the material from the first three exams in
the regular Physics 218 sections, inclusively,
and will in no way count towards your final class
grade. It is, in some sense, simply for fun and a
way to match your physics skills against the very
best here at AM. This semester, the exam will be
held at 600 p.m. on Monday, December 1, in
classroom 202T of the Engineering Physics
Building (ENPH). If you are interested in
competing for this award (which includes a
certificate, as well as a book and a monetary
award), please contact Sandi Smith in ENPH Room
421, 845-7738, or smiths_at_tamu.edu, at your
earliest convenience. Please include your name,
instructors name, major, UIN, and an e-mail
address where we can reach you. We would
appreciate your response no later than Friday,
November 28, 2008. As an added incentive, all
students who perform well on the challenge exam
will be named Addison Wesley / Benjamin Cummings
Mechanics Scholars and be invited to a catered
lunch in room 205 of the MSC December 4 (reading
day), from 1200 to 130 p.m. in their honor. In
addition to lunch, we will have presentations by
faculty members about potential careers for
people with high levels of physics problem
solving skills. We hope to hear from you soon as
only a limited number of seats for the exam
exist.
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Rotational Kinetic Energy
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A primitive yo-yo is made by wrapping a string
several times around a solid cylinder with mass M
and radius R. You hold the end of the string
stationary while releasing the cylinder with no
initial motion. The string unwinds but does not
slip or stretch as the cylinder drops and
rotates. Use energy considerations to find the
speed vcm of the center of mass of the solid
cylinder after it has dropped a distance h.
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Challenge Exam

• Announcement of this semesters 218 Challenge
  Exam Monday December 1st at 600PM
• Not required (just for fun)
• Does not (will not!!!) count as part of your
  final grade
• Test your skills against the best Aggies from all
  the Physics 218 sections (not just this lecture)
  on Physics 218 material
• Students who perform well will be recognized as
  Mechanics Scholars, and honored at a banquet in
  their honor. Other prizes, including cash.

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Ch. 17 Statics
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There is a ladder against a wall. There is no
friction at the wall and the coefficient of
friction at the floor is ?. At what angle can the
ladder be placed so that it would slip if the
angle were decreased infinitesimally?
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The advantage of a lever
GIVE ME A PLACE TO STAND AND I WILL MOVE THE
EARTH                                             
     
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(No Transcript)
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The advantage of a pulley
What minimum force F is needed to lift the piano
of mass M?
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Harmonic Motion
Simple harmonic oscillator
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Examples

• Lots of stuff Vibrates or Oscillates
• Radio Waves
• Guitar Strings
• Atoms
• Clocks, etc

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Why do we care?

• Lots of engineering problems are oscillation
  problems
• Buildings vibrating in the wind
• Motors vibrating when running
• Solids vibrating when struck
• Earthquakes

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The forces
No force
Force in x direction
Force in x direction
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More Detail
Time
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Some Terms
Amplitude Max distance Period Time it takes
to get back to here
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• A block with mass m is attached to the end of a
  spring, with spring constant k. The spring is
  stretched a distance L and let go at t0
• Find the position of the mass at all times
• Where does the maximum speed occur?
• What is the maximum speed?

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Resonance