1. Motion11.3 Acceleration Chapter 11

2. What are we going to learn? • What is acceleration? • How to calculate acceleration and interpret speed vs. time graphs

3. Acceleration • Rate at which velocity changes

4. Acceleration • Can be described as changes in: speed, direction, or both

5. It is a vector • 2 types: constant and free fall

6. This change may be due to either an increase or a decrease in speed • Positive: increasing change in speed • Negative: decreasing change in speed

7. Acceleration Animation • http://www.physicsclassroom.com/mmedia/kinema/avd.cfm • http://www.physicsclassroom.com/mmedia/kinema/acceln.cfm

8. Constant Acceleration • A steady change in velocity

17. If the velocity increases, the numerator is positive so acceleration is positive • If the velocity decreases, the numerator isnegative so acceleration is negative

18. Free Fall • Movement of an object toward Earth solely because of gravity • Due to change in speed • Rate of change in speed is 9.8 meters per second per second (9.8 m/s2)

19. Changing Direction • Acceleration may be due to its direction constantly changing even though it is traveling at constant speed • Ex: horse on a carousel

20. Changing Direction & Speed • Sometimes motion is changing in both speed and direction at the same time • Ex: skier on a downhill run

21. Acceleration Calculation • Calculation for straight-line motion: divide the change in velocity by the total time

22. This equation defines the average acceleration • A change in velocity by a constant amount each second (its position changes by a constant amount each second)

23. Acceleration Graphs • Acceleration is the slope of a speed-time graph

24. In a linear graph, the displayed data form straight-line parts

25. In a nonlinear graph, a curve connects the data points that are plotted

26. Instantaneous Acceleration • How fast a velocity is changing at a specific instant

27. Example • A snow skier is traveling at 15 m/s at one instant and at 22 m/s 2 seconds later. What is her acceleration?

28. If she maintains this constant acceleration, how fast will she be traveling one second later?

29. Acceleration Graph

30. Questions... Acceleration is a change in is measuredin units of direction speed m/s2

31. The rate at which velocity changes is called acceleration.

32. In terms of speed and direction, in what ways can an object accelerate? Increase or decrease speed, change direction, or both change speed and direction.

33. Because acceleration is a quantity that has both magnitude and direction, it is a(n) vector.

34. True or false? Acceleration is the result ofincreases or decreases in speed. True

35. Ignoring air resistance, a rock in free fall will have a velocity of 39.2 m/s after 4.0 seconds. (9.8 m/s2)(4.0 s)

36. A horse on a carousel that is moving at a constant speed is accelerating because it is constantly changing direction

37. Write the equation used to calculate the acceleration of an object . • Acceleration = change in velocity divided by the total time

38. True or false? When the final velocity isless than the initial velocity of an object, the acceleration is negative. True

39. A skateboarder begins down a ramp at a speed of 1.0 m/s. After 3 seconds, her speed has increased to 4.0 m/s. Calculate her acceleration. a. 1.0 m/s2 b. 3.0 m/s2 c. 5.0 m/s2 d. 9.8 m/s2

40. Graph A represents the motion of a downhill skier. How fast was the skier moving after traveling down the hill for 2.5 seconds? 10 m/s

41. In which graph does an object move at constant speed during the first 4 seconds? Graph B

42. Graph B represents the motion of a mountain biker. What is the biker’s speed at times of 10 s and 20 s?

43. Graph B represents the motion of a mountain biker. What is the biker’s speed at times of 10 s and 20 s? 5 m/s 0 m/s

44. Determine the acceleration of the mountain biker during the 10 second to 20 second time period. Show your work. 0 m/s – 5 m/s = - 5 m/s = -0.5 m/s2 20 s – 10 s 10 s

45. The plotted data points representing acceleration in a distance-time graph form a(n) curved line.

46. The measure of how fast a velocity is changing at a specific instant is known as instantaneous acceleration.