Velocity and Acceleration: Understanding Motion

1. Relative Velocity Pre-Class Friday 1-13-12 Garfield is walking at 1 m/s, but the wind is blowing him at -3 m/s. What velocity does Jon think he has?

2. Uniform motion: constant speed or velocity Nonuniform motion: changing speed or velocity Chapter 3: Accelerated Motion

3. Measuring velocity (in meters per second, m/s) • Velocity interval is defined as: Δv= vf - vi • The i is initial and the f is final D (Greek letter “delta”) stands for “change in” or final - initial

4. Acceleration is the measure of the change in velocity over a given time Constant velocity means no acceleration Dv a = Dt ACCELERATION a: average acceleration (m/s2) v: velocity (m/s) t: time (s)

5. Velocity-Time graph • Similar to Position-Time graph • Displays the velocity of an object at any time • Slope of the line shows the average acceleration

6. Pre-Class for Tuesday 1-17-12 All of the following can be found on a velocity-time graph except for: • Average acceleration • Inertia • Velocity • Time

7. EQUATIONS OF MOTION vf = vi + a t x = vi t + 1/2 a t2 vf2 - vi2 = 2 a x x = (vf + vi) t/2

8. Section 3.2 Pre-class for Wednesday 1-18-12 • vf = vi + at • vf = vi + 2at • vf2 = vi2 + 2at • vf = vi– at A car is moving with an initial velocity of vi m/s. After reaching a highway, it moves with a constant acceleration of a m/s2, what will be the velocity of the car after traveling for t seconds?

9. ACCELERATION BY GRAVITY • The Earth constantly accelerates all objects towards its center • We use the variable g for the acceleration of gravity • g = 9.8 m/s2 • a = - g = - 9.8 m/s2 (different from book)

10. Taking a closer look…

11. EQUATIONS OF MOTION vf = vi - g t y = vi t - 1/2 g t2 vf2 - vi2 = - 2 g y

12. 80. 8 m/s2 81. 33 m/s 82. 6 m/s2, 0 m/s2, -2 m/s2, -4 m/s2 85. Car B,Car A&C tie 86. 607 m/s, 1.83 mach 89. 43.2 m, 43.2 m 138m, 550m 92. 924 m 94. 60 m/s 95. 50 m; yes, 21.76 m/s 97. 1.2 s 98. -78 m/s, -310 m 99. -20 m/s, -20 m 100. -7.3 m/s 102. 5.9 m, 10.8 m/s 105. 8 m 107. 280 m/s2, 29g 109. 3.1x108 m/s2, 11ms 113. 1.56 m 115. -15 m/s,-10 m, 20 m CHAPTER 3

13. Section 3.2 Pre-class Thursday 1-19-12 What is the accepted value for the acceleration of gravity?

14. FALLING LAB • Materials: • 6 pennies • stop watch • meter stick • tape • Objective: • determine the acceleration of gravity • Each group will turn a paper into me today.

15. PROCEDURES • Stack five pennies and tape them together. • Drop the five pennies from 3 different heights. • Measure the distance fallen and the time it took to fall to the ground. • Determine the acceleration of gravity. • Repeat the experiment for the single penny. • Complete the chart on the next slide and answer the questions.

16. FILL OUT THE CHART • Find the percent difference between your answer and the accepted answer. • How could you improve your results (at least 2 examples)? Questions

17. EQUATIONS OF MOTION vf = vi + a t x = vi t + 1/2 a t2 vf2 - vi2 = 2 a x

18. Pre-class Thursday 1-22-09 Write: “Review 4 test”

19. TEST OVER CHAPTER3 • Take a few minutes to review/finish pre-class problems. • You need your own paper. • Do not write on my paper. • Box in final answers. • Write clearly. • You may need a calculator.