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PHSX213 class

PHSX213 class. Questions from last time ? Vectors recap Class news Vectors quiz Doing homework Describing Motion (Kinematics) Chapter 2 leading into 4. What is a vector?. A quantity having both size and direction The rate of change of velocity

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PHSX213 class

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  1. PHSX213 class • Questions from last time ? • Vectors recap • Class news • Vectors quiz • Doing homework • Describing Motion (Kinematics) • Chapter 2 leading into 4.

  2. What is a vector? • A quantity having both size and direction • The rate of change of velocity • A number defined by an angle and a magnitude • The difference between initial and final displacement • None of the above

  3. What is a vector? • A quantity having both size and direction • The rate of change of velocity • A number defined by an angle and a magnitude • The difference between initial and final displacement • None of the above

  4. What is the name of the quantity represented as • Eye-hat • Invariant magnitude • Integral of motion • Unit vector in x-direction • Length of the horizontal axis

  5. What is the name of the quantity represented as • Eye-hat • Invariant magnitude • Integral of motion • Unit vector in x-direction • Length of the horizontal axis

  6. What’s a unit vector ?

  7. Diagnostic Test • Average score: 16.6/30 • A couple of you did really well – do you want to teach the class ? • Scores 20-24. You’ve already got a good grasp of many of the concepts. • Scores 15-19. This is about the score I would expect. Room for learning/improvement ! • Lower scores. • Either little previous exposure to physics, or quite a few misconceptions which we’ll need to work on. • Please take this positively as a wake-up call that you’ve got a lot to learn/learn properly in this course.

  8. Syllabus remarks • Will be very similar to last semester at least until the 2nd midterm. • Syllabus should be published on Friday.

  9. Schedules • Office Hours. • By appointment and, • Wed. 2:30 – 4:00 PM ? • Extra review sessions on developing problem solving skills • Occasionally, Wed. evening 6:00 PM – 7.15 PM ? • Normal homework deadlines. • Written stuff – in class. • Weekly online homework, Friday 6 PM. (will usually be published by Thursday of previous week). • Deadline chosen to minimize interference with lab. report deadlines.

  10. Mid-Term Exams • Time : 8:00 PM – 9:30 PM • Wednesday February 16th • Wednesday March 16th • Wednesday April 20th • 3 classes will be “NO CLASS” days. • For sure, March 18th (Friday before Spring Break).

  11. Web Site • Now has links to : • Registration of your H-iTT clicker • Lecture Notes

  12. Labs • Labs are an important part of the course. • They will carry 20% of the course credit, and there are severe penalties for missing labs. • The MX project is especially important. • Most lab. issues need to be discussed with Mr. Curry.

  13. Homework • There will be approximately 15 homework assignments. • The overall course weight will be between 15 and 20%. • Each homework assignment will carry the same weight unless otherwise announced. • Most of each homework assignment will be completed online.

  14. HRW end-of-chapter problems : 1.12 1.20 2.22 2.56 3.22 To be handed in by Monday in class. Please use a separate page of paper for each question. Allows me to give feedback on eg. a subset of the questions. Draw diagrams (almost always a good idea). Explain assumptions and use symbols to solve problems algebraically before sticking in numbers. Homework Assignment 1

  15. Timelines • I should have the HiTT clicker stuff working on Friday. • I’ll expect you to have one by Monday. • Class homework assignment and online resources page with eGradePlus stuff should be available by this Friday (if not before).

  16. Which figure shows

  17. Which figure shows

  18. Which figure shows

  19. Which figure shows

  20. What are the x- and y-components Cx and Cy of vector Cx= –3 cm, Cy = 1 cm Cx= –4 cm, Cy = 2 cm Cx= –2 cm, Cy = 1 cm Cx= –3 cm, Cy = –1 cm Cx= 1 cm, Cy = –1 cm

  21. What are the x- and y-components Cx and Cy of vector Cx= –3 cm, Cy = 1 cm Cx= –4 cm, Cy = 2 cm Cx= –2 cm, Cy = 1 cm Cx= –3 cm, Cy = –1 cm Cx= 1 cm, Cy = –1 cm

  22. Worked out example emphasising using symbols for problem solutions • HRW Chapter 3 question 24 • An explorer is caught in a whiteout while returning to base camp. He was supposed to travel due north for 5.6 km, but when the snow clears, discovers that he actually traveled 7.8 km at 50º north of due east. • How far and in what direction must he travel to reach base camp ?

  23. Worked out example emphasising using symbols for problem solutions • HRW Chapter 3 question 24 • Step 1. Draw diagram • Step 2. Define variables on diagram • Step 3. Write down concept you will use to solve the problem • Step 4. Solve the problem algebraically • Step 5. Plug in numerical values.

  24. Examples of Motion

  25. The slope at a point on a position-versus-time graph of an object is the object’s speed at that point. the object’s average velocity at that point. the object’s instantaneous velocity at that point. the object’s acceleration at that point. the distance traveled by the object to that point.

  26. The slope at a point on a position-versus-time graph of an object is the object’s speed at that point. the object’s average velocity at that point. the object’s instantaneous velocity at that point. the object’s acceleration at that point. the distance traveled by the object to that point.

  27. Falling Dollar • The reason I’m not planning a European vacation this summer ! (joke)

  28. Kinematics: Describing Motion • Reference frame • Origin + Co-ordinate axes. x-axis, (x,y)-axes, (x,y,z)-axes • Position (location within the co-ordinate axes) • Displacement, is defined as (≡) Change in position • Velocity ≡ Rate of change in position with time • Acceleration ≡ Rate of change in velocity with time

  29. Position vector for a particle

  30. Kinematics: General Case (3-D) • Reference frame • Origin, (x, y, z)-axes • Position Vector, r = x i + y j + z k • Displacement, ≡ Dr = r2 – r1 • Instantaneous Velocity, v≡ d r /dt • Instantaneous Acceleration, a ≡ d v/dt ≡ d2 r /dt2 • We will return to these more general definitions when we discuss motion in more than 1-d. ^ ^ ^ → → → → → → → → →

  31. Kinematics: Special Case (1-D) Up-down Ball , Car demo • Reference frame • Origin, (x, y, z)-axes • Position Vector, x = x i • Displacement, ≡ Dx = x2 – x1 • Instantaneous Velocity, v≡ d x /dt • Instantaneous Acceleration, a ≡ d v/dt ≡ d2 x /dt2 ^ → Draw graphs → → → → → → → →

  32. Draw graphs • Eg. basketball. • When is the magnitude of its acceleration the largest ?

  33. What does all this mean ? • Position • Displacement (change in position over a time interval) • Velocity • Is synonymous (to me) with instantaneous velocity • average velocity, vave≡ Dr / Dt • Speed = magnitude of the velocity. • Acceleration • Instantaneous acceleration • average acceleration, aave≡ Dv / Dt • Can something traveling with constant speed be accelerating ?

  34. Kinematic Equations • In general. • Will be useful for lab project, MX • Specific case of CONSTANT acceleration

  35. Meter stick • Reaction time measurement

  36. Friday • More 1-d kinematics (chapter 2) • And start 2-d motion (chapter 4) • particularly projectiles • uniform circular motion

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