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Outline. Position versus Time. Welcome to the x-axis Speeding up, Slowing down Graphing position versus time Uniform Motion. 3125 2761 Mdcl1 Mdcl!. Kinematics in 1 dimension. As opposed to WHY an object moves. Kinematics is all about predicting where an object will be in the future

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Outline

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  1. Outline Position versus Time • Welcome to the x-axis • Speeding up, Slowing down • Graphing position versus time • Uniform Motion 3125 2761 Mdcl1 Mdcl!

  2. Kinematics in 1 dimension As opposed to WHY an object moves • Kinematics is all about predicting where an object will be in the future • Kinematics doesn’t tell us about WHY an object is moving, only WHERE • 1-D motion describes motion that is constrained to move along a line • To describe motion in 1 dimension, a coordinate system must be created What do you need for a 1-D coordinate system

  3. Walk–No Motion Describe the path x [m] t [s]

  4. Walk–Const +ve Speed Describe the path x [m] t [s]

  5. Walk–Const –ve Speed Describe the path x [m] t [s]

  6. Walk–Back/Forth Describe the path x [m] t [s]

  7. Walk–Back/Forth Walk the path x [m] t [s]

  8. Walk–Two +ve Speeds Describe the path x [m] t [s]

  9. The slope of a position vs. time graph tells us an object’s speed. Why? This equation has a familiar form…

  10. QQ12: x vs. t Quick Quiz:John leaves class and walks in a straight line directly toward his residence. He starts at a position which is 300 m away from the residence, and walks at a constant speed. After 150 s, he arrives at his residence. Which of the following position-time graphs represents his motion over this period, if his residence is at the origin? x [m] x [m] 300 A. C. 300 0 0 150 0 t [s] 150 0 t [s] x [m] x [m] 300 300 D. B. 0 0 150 0 t [s] 150 0 t [s]

  11. QQ13: simultaneity • Quick Quiz: At the moment that John leaves class, Monica leaves the residence and heads directly toward the classroom that John is leaving. Having walked there before, Monica knows that the trip would take her exactly 100 s. • At what time does Monica bump into John? • 60s • 100s • 150s • Not enough information to know for sure.

  12. Answer QQ13 The d-t graph 300 John x [m] Monica 0 150 100 0 t [s]

  13. Solution:

  14. QQ14: speed Example A parachutist opens her parachute at an altitude of 1500 m. She then descends slowly to earth at a steady speed of 5 m/s. Sketch a position versus time graph for her motion. Start your graph as her parachute opens. (There are enough numbers here that you can make a real graph. Include values for the x and t intercepts)

  15. QQ15: intersection A x [m] B 1 3 2 4 t [s] Quick Quiz: At what time do objects A & B have the same speed? A. 0s B. 3s C. never D. all the time

  16. Do for next class: • Read: sections 2.3, 2.4 (don’t worry about the integrals, but be sure to understand Stop To Think 2.3) • Suggested problems: 2.10, 2.11

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