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Announcements

Announcements. CAPA #11 due this Friday at 10 pm Reading: Chapter 9.1-9.4 Section – this week Lab #4: Rotations Midterm Exam #3 on Tuesday November 8 th , 2011  details given on next slides!  practice exam and solutions on CULearn  formula sheet and info. posted on web page

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Announcements

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  1. Announcements • CAPA #11 due this Friday at 10 pm • Reading: Chapter 9.1-9.4 • Section – this week Lab #4: Rotations • Midterm Exam #3 on Tuesday November 8th, 2011 •  details given on next slides! •  practice exam and solutions on CULearn •  formula sheet and info. posted on web page • Fraction of all clicker questions answered posted on CULearn. Email me with your clicker ID, name, student ID if you believe it is incorrect.

  2. Exam #3 Information Tuesday, November 8th, 2011 7:30 – 9:15 pm Location: Same as last two exams (see info page) The third exam will cover material including Chapters 1-8; CAPA homework assignments 1-11; Lecture Material through Monday, October 31, and all Section labs and assignments including the week of October 31-November 4. Note that the strong emphasis will be on material since that last midterm (i.e. Chapters 6-8, CAPA 8-11, etc.); however, much of the new material builds upon the earlier material. The exam will be 20-25 multiple choice questions. The exam is closed book and closed notes. Calculators are allowed, but no sharing of calculators. A formula sheet will be included with your exam, and a preview of that identical sheet is linked here as a PDF file. There is no need to print and bring this sheet as a copy will be included with the exam. A practice exam and solutions are available on the course CULearn page.

  3. CH. 6 Work and Energy 6.1 Work done by a constant force 6.3 Kinetic Energy and Work-Energy Prinl. 6.4 Potential energy 6.5 Conservative and non-conservative forces 6.6. Mechanical energy (M.E.) & its conservation 6.7 Problem solving using conservation of M.E. 6.8 Other forms of energy, energy transformation, Conservation of Energy (C.E.) 6.9 C.E. with dissipative forces 6.10 Power

  4. CH. 7 Linear Momentum 7.1 Momentum & its relation to force 7.2 Conservation of Momentum (C.M.) 7.3 Collisions & impulse 7.4 Collisions: C.E. & C. M. 7.5 Elastic collisions in 1D 7.6 Inelastic collisions

  5. CH. 8 Rotational Motion 8.1 Angular quantities 8.2 Constant angular acceleration 8.3 Rolling motion 8.4 Torque 8.5 Rotational dynamics (R.D.): torque and rotational inertia 8.6 Solving problems in R.D. 8.7 Rotational Kinetic Energy 8.8 Conservation of Angular Momentum

  6. Schedule Today Help Room Hours 1:45 pm – 3:45 pm Reminder – Dr. Ariel Paul optional review sessions Wednesdays at 8:00 pm in Duane G125. Monday in class – exam review clicker questions by Professor Uzdensky. No office hours on Monday 2-3 pm.

  7. Clicker Question Room Frequency BA A wheel of radius 2 meters is rolling without slipping at a constant angular velocity of 5 revolutions per minute. Which is an equivalent expression for w? (1/6) p radians/second (10) p radians/second (1/3) p radians/second (2/3) p radians/second None of the above In two minutes, how far has the wheel traveled (translation)? 0 meters 10 meters 5p meters 40pmeters None of the above

  8. Conservation of Angular Momentum Recall: Momentum p = mvL = IωAngular momentum Relation to force F = Δp/Δtτ = ΔL/ΔtRelation to torque No external force Δp= 0 ΔL = 0No external torque (momentum is conserved) (angular momentum is conserved) Li= Lf Iiωi = Ifωf

  9. Clicker Question Room Frequency BA A child stands on the edge of a merry-go-round. The child slowly walks towards the center of the platform. As the child moves toward the center, the platform’s rotation rate: Increases Decreases Stays the same

  10. Clicker Question Room Frequency BA Consider a solid disk of mass M and radius R with an axis through its center. An ant of mass m is placed on the rim of the disk. The mass-disk system is rotating. The ant walks toward the center of the disk. The magnitude of the angular momentum L of the system: A) increases B) decreases C) remains constant As ant moves inward, the kinetic energy of the system: A) increases B) decreases C) remains constant Unless an outside torque is applied, L = Iω= constant. Because I reduces, ω increases from the ant’s motion.

  11. Clicker Question Room Frequency BA A star is rotating with a period of T. Over a span of a million years, its radius decreases by a factor of 2.0 due to using up its nuclear fuel. What is the new period of the star? (Recall: Isphere = (2/5) MR2) T/2 B) 2T C) 4T D) T/4 E) None of these. Conservation of Angular Momentum:

  12. Stars shine by converting Hydrogen to Helium (nuclear fusion). When all the hydrogen is gone, gravity causes the star to collapse inward (sometimes to a neutron star). The star radius can change from 1 million miles to 30 miles! This is a factor of 30,000. Moment of inertia drops by (3x104)2 ~ 1 billion Sun rotates around its axis every 24 days. After a collapse, it would revolve 500 times per second

  13. Pulsar

  14. Bicycle Wheel Demonstration

  15. Static Equilibrium

  16. Static Equilibrium Static Equilibrium: An object is (1) not translating (not moving up, down, left, right) (2) not rotating (not spinning CW or CCW). (net force is zero) Not translating: (each component of the net force is zero) Not rotating: (net torque is zero)

  17. Clicker Question Room Frequency BA Is the net force on the metal bar zero? A) Yes B) No L Is the the metal in static equilibrium? A) Yes B) No Consider rotations about the middle of the bar. Net positive torque will cause the bar to rotate (CCW). Fnet= 0 but the bar will rotate anyway.

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