2. If Alice walks forward on a bus 2 meters while the bus moves forward 10 meters, How far does Alice walk according to the passengers? Motion and Position 2.1 Describing Motion How far does Alice walk according to Arlo standing at the side of the road?

3. A reference point is needed to determine the position of an object. Motion and Position 2.1 Describing Motion The motion of an object depends on the reference point that is chosen

4. If you are sitting in a chair reading this sentence, you are moving. You are not moving relative to your desk or your school building, but you are moving relative to the other planets in the solar system and the Sun. Relative Motion 2.1 Describing Motion

5. Distance is: how far an object has moved. Symbol: d Unit m Longer distances are measured in kilometers (km). Distance 2.1 Describing Motion

6. Displacement is the distance and direction of an object's final position compared to its initial position. Symbol: d Unit m The key here is DIRECTION so an object’s path does not matter Displacement 2.1 Describing Motion

7. The distance around a track once is 400 meters (1/4 mile) What is the runner’s displacement? How does a car measure distance? Distance versus displacement 2.1 Describing Motion

8. Arlo travels 50 m in the original direction (north) plus 30 m in the opposite direction (south), so the total distance she ran is 80 m. Distance 2.1 Describing Motion Suppose Arlo jogs to the 50-m mark and then turns around and runs back to the 20-m mark.

9. The displacement of the runner is only 20 m because you only look at where the runner starts and stops. Arlo stops 20m north from the starting position Displacement 2.1 Describing Motion

10. Speed 2.1 Describing Motion Speed is how fast an object moves Symbol: v Unit: m/s

11. Velocity 2.1 Describing Motion Velocity is how fast an object moves and the direction it moves Symbol: v Unit: m/s

12. Because velocity depends on direction as well as speed, the velocity of an object can change even if the speed of the object remains constant. Velocity 2.1 Describing Motion The speed of this car might be constant, but its velocity is not constant because the direction of motion is always changing.

13. Any change over time is called a rate. If you think of distance as the change in position, then speed is the rate at which distance is traveled or the rate of change in position. Velocity (in meters/second)= displacement (m) d = v t dtime (s) v t Calculating Velocity 2.1 Describing Motion

14. Sirius is moving away from our solar system with a speed of about 17.8 km/s. How far will this star travel in 2590 years (convert to seconds), the time it takes for Sirius to move one degree across the sky? Calculating Distance 2.1 Describing Motion 1.45x10 12 meters

15. Sound travels at a speed of 330 m/s. If you hear thunder 3 seconds after seeing lightning, how far away is the lightning? Calculating Distance 2.1 Describing Motion 990 meters

16. The motion of an object over a period of time can be shown on a distance-time graph. Graphing Motion 2.1 Describing Motion Time is plotted along the horizontal axis of the graph and the distance traveled is plotted along the vertical axis of the graph. Click image to play movie

17. Plotting a Distance-Time Graph 2.1 Describing Motion Displacement (m) time (s) 1 2 3 4 5 6 7 8 9 10 -30 -20 -10 0 10 20

18. Plotting a Distance-Time Graph 2.1 Describing Motion Slope is the steepness of the line Slope = (y 2 -y 1 ) or rise (x 2 -x 1 )run

19. Grace the cat Plotting a Distance-Time Graph 2.1 Describing Motion Displacement (m) time (s) 1 2 3 4 5 -1 0 1 2 3

20. An object at rest is a Horizontal line An object traveling with a constant velocity is a straight line with a slope Plotting a Distance-Time Graph 2.1 Describing Motion Slope = steeper Slope= velocity or speed Sign= direction: Positive= right or up

21. 2.1 Question 1 What is the difference between distance and displacement? Section Check

22. 2.1 Answer Distance describes how far an object moves; displacement is the distance and the direction of an object’s change in position. Section Check

23. 2.1 Question 2 __________ is the distance an object travels per unit of time. Section Check A. acceleration B. displacement C. speed D. velocity

24. 2.1 Answer The answer is C. Speed is the distance an object travels per unit of time. Section Check

25. Acceleration, Speed and Velocity Acceleration is how quickly velocity changes. When the velocity of an object changes, the object is accelerating. Symbol: a Unit: m/s 2 http://glencoe.mcgraw- hill.com/sites/dl/free/0078600510/161752/00035808.html 2.2 Acceleration

26. Change in velocity Initial velocity is the beginning velocity ( starts from rest= zero). Symbol: v i Unit: m/s Final velocity is the ending velocity (if the object ends at rest= zero). Symbol: v f Unit: m/s 2.2 Acceleration

27. Speeding Up and Slowing Down When you think of acceleration, you probably think of something speeding up. However, an object that is slowing down also is accelerating. Acceleration also has direction, just as velocity does. 2.2 Acceleration Acceleration can be speeding up, slowing down, or changing direction

28. Changing Direction The speed of the horses in this carousel is constant, but the horses are accelerating because their direction is changing constantly. 2.2 Acceleration

29. Calculating Acceleration 2.2 Acceleration To calculate the acceleration of an object, the change in velocity is divided by the length of time interval over which the change occurred. v f - v i a t

30. Calculating Acceleration 2.2 Acceleration Because it started from rest, its initial speed was zero. A ball is dropped from a cliff and has an acceleration of 9.8 m/s 2. How long will it take the ball to reach a speed of 24.5 m/s?

31. Amusement Park Acceleration Engineers use the laws of physics to design amusement park rides that are thrilling, but harmless. 2.2 Acceleration The highest speeds and accelerations usually are produced on steel roller coasters.

32. Graphing Acceleration Speeding up Slowing down 2.2 Acceleration displacement time

33. 2.2 Question 1 Acceleration is the rate of change of __________. Section Check

34. 2.2 Answer The correct answer is velocity. Acceleration occurs when an object changes its speed, direction, or both. Section Check

35. 2.2 Question 2 Which is NOT a form of acceleration? Section Check A. maintaining a constant speed and direction B. speeding up C. slowing down D. turning

36. 2.2 Answer The answer is A. Any change of speed or direction results in acceleration. Section Check

37. 2.2 Question 3 What is the acceleration of a hockey player who is skating at 10 m/s and comes to a complete stop in 2 s? Section Check A. 5 m/s 2 B. -5 m/s 2 C. 20 m/s 2 D. -20 m/s 2

38. 2.2 Answer The answer is B. Calculate acceleration by subtracting initial velocity (10 m/s) from final velocity (0), then dividing by the time interval (2s). Section Check (0 m/s – 10 m/s) = – 5 m/s 2s

39. 2.2 Question 4 Describe the motion of each graph. Section Check