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Announcements

Announcements. Homework for tomorrow… (Ch. 2, Probs 6 & 13) Labs begin next week Office hours… M 3-4 pm TWR 9-10 am F 1-2 pm Tutorial Learning Center – Houston Hall 113 MWR 8 am-6 pm T 8 am-7 pm F 8 am-5 pm. Chapter 2.

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Announcements

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  1. Announcements • Homework for tomorrow… (Ch. 2, Probs 6 & 13) • Labs beginnextweek • Office hours… M 3-4 pm TWR 9-10 am F 1-2 pm • Tutorial Learning Center – Houston Hall 113 MWR 8 am-6 pm T 8 am-7 pm F 8 am-5 pm

  2. Chapter 2 Motion Along a Straight Line (Displacement, Velocity, & Speed)

  3. Unit Vectors… • point along coordinate axes • have unit length i.e.’s: - unit vector along x-axis - unit vector along y-axis - unit vector along z-axis

  4. Displacement • defined as the change in position • is the “initial” position • is the “final” position

  5. Displacement cont.. i.e.’s • A particle starts at 5 m, moves to 2 m, then returns to5 m

  6. Displacement vs. Distance Displacement is NOT the same as Distance i.e. Throw a ball straight up and then catch it at the same point you released it • The distance is twice the height • The displacement is zero

  7. Average Velocity… • is the displacement divided by the time interval in which it occurs • is a vector quantity • Units?

  8. Graphical Interpretation of Velocity Average velocity equals the slope of the line joining the initial and final positions (vs. time)

  9. Position vs. Time Graphs What will the position vs. time graph look like for the following: • Stand still • Slow steady walk • Fast steady walk • How should I move to reproduce the graph on the previous slide?

  10. Quiz Question 1 A person initially at point P in the illustration stays there a moment and then moves along the axis to Q and stays there a moment. She then runs quickly to R, stays there a moment, and then strolls back to P. Which of the position vs. time graphs below correctly represents this motion?

  11. Average Speed the totaldistance traveled divided by the total time elapsed • Speed is a scalar quantity • Average speed completely ignores any variations in the object’s actual motion

  12. Speed vs. Velocity Cars on both paths have the same average velocity… Why? • … they have the same displacement (in the same time interval). The car on the blue path will have a greater average speed…Why? • … the distance it travels is larger (in the same time interval)!

  13. Reading Exercise 2-4 Suppose that you drive 10 mi due east to a store. You suddenly realize that you forgot your money. You turn around and drive the 10 mi due west back to your home and then return to the store. The total trip took 30 min. • What is your average velocity for the entire trip? (Set up a coordinate system and express your result in vector notation) • What was your average speed for the entire trip? • Discuss why you obtained different values for average velocity and average speed.

  14. Instantaneous Velocity • the limit of the average velocity as the time becomes infinitesimally small

  15. Instantaneous Velocity Instantaneous velocity equals the slope of the tangent of a position vs time curve

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