1 / 18

PHSX213 class

PHSX213 class. Class stuff MidTerm Exam 2 Wed. March 16 th 8:00 – 9:30 PM Chapters 7-11 Budig 120 (same area as before) Practice Exam Answers on web No classes on Wed., Fri. More on Angular Momentum/Review. Exam Big Picture. Energy Conservation Momentum Conservation

jerom
Download Presentation

PHSX213 class

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. PHSX213 class • Class stuff • MidTerm Exam 2 • Wed. March 16th 8:00 – 9:30 PM • Chapters 7-11 • Budig 120 (same area as before) • Practice Exam • Answers on web • No classes on Wed., Fri. • More on Angular Momentum/Review

  2. Exam Big Picture • Energy Conservation • Momentum Conservation • Angular Momentum Conservation And understanding the necessary conditions for these to apply.

  3. Correspondences between linear and rotational motion

  4. Exam Stuff : Missing Equations • Krot = ½ I w2 • w = v/r ; atan = a r • Emech = K + U • DEmech = WNC • Exam will be 25 multiple choice questions. • Time = 90 minutes (not 150 mins)

  5. Clarification • On Friday, we were discussing how to calculate the net torque. • One has to calculate this consistently with respect to the same point. In general, it is really only useful to calculate it about the rotation axis. • Only for the special case of equilibrium, where the net force is zero, does one have the freedom to choose the reference point.

  6. Check-Point 1 • The motion of two balls before and after a collision is shown. Ball 1 chases Ball 2. The speed of Ball 1 is 4 m/s and the speed of Ball 2 is 3 m/s. After the collision Ball 1 rebounds at 3 m/s, and Ball 2 speeds away at 4 m/s. The mass of each ball is 1 kg. Which one statement is true ? • A) Momentum was not conserved during the collision, so there must have been some external force acting that we’re not told about. • B) Kinetic energy was not conserved during the collision • C) The momentum change for Ball 1 is +7 kg m/s • D) The momentum change for Ball 2 is +7 kg m/s • E) All of the above are true. after before +x 2 1 2 1

  7. Torque Definition for a Particle t = r F Vector product means that the torque is directed perpendicular to the plane formed by (r, F). Whether it is up or down is from the right-hand rule convention NB Only makes sense to talk about the torque wrt or about a certain point

  8. Angular Momentum Definition for a Particle l = r p = r m v NB Only makes sense to talk about the angular momentum wrt or about a certain point

  9. Angular Momentum Definition for a Rigid Body About a Fixed Axis L = Sli = I w In analogy to P = M v

  10. Newton II for Rotation • S F = dp/dt ( the general form of Newton II) • St = dl/dt • It is the net torque that causes changes in angular momentum.

  11. Angular Momentum Conservation • Just as for Newton II for linear motion where if the net force was zero, dp/dt =0 => p conserved. • For rotational motion, if the net torque is zero, dl/dt =0, so l conserved.

  12. Angular Momentum Conservation Problems This is a situation where using both the particle and rigid body definitions of angular momentum is useful.

  13. Kepler’s Second Law Each planet moves so that a line drawn from the Sun to the planet sweeps out equal areas, A, in equal periods of time. ie. dA/dt = 0

  14. Runner on circular platform

  15. Clutch design

  16. Check-Point 2 • The angular momentum vector of Earth about its rotation axis, due to its daily rotation, is directed: • A. tangent to the equator toward the east • B. tangent to the equator toward the west • C. north • D. southwest • E. towards the Sun

  17. Why does a rolling sphere slow down ?

  18. Turnstile problem

More Related