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Chapter 11

Chapter 11. Motion. 11.1 Distance & Dispalcement. Motion. Describing Motion. Two parts of describing motion 1. Speed 2. Direction. Frame of Reference. Definition - A system of objects that are not moving with respect to one another. Relative Motion.

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Chapter 11

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  1. Chapter 11 Motion

  2. 11.1 Distance & Dispalcement Motion

  3. Describing Motion • Two parts of describing motion • 1. Speed • 2. Direction

  4. Frame of Reference • Definition - A system of objects that are not moving with respect to one another Relative Motion • Definition – Movement in relation to a frame of reference • For example, does a person sitting on a moving train have motion? It all depends on the frame of reference

  5. Tennis Ball Movement & Frame of Reference Demonstration

  6. Distance • The length of a path between two points • In other words, distance is the length of a path connecting an objects starting point and its ending point • SI unit for distance is the meter

  7. Displacement • Definition – The direction from the starting point and the length of a straight line from the starting point to the ending point • Example – What would your displacement be if you rode a rollercoaster?

  8. Baseball Example • If you hit a home run in baseball, you would run from home plate, to each of the bases (1 through 3) and then back to home plate. If there is a distance of 30 meters between each of the bases, what is the total distance you run? What is your displacement?

  9. Vector • Definition – A quantity that has both magnitude (size, length or amount) and direction • Represented using arrows • Displacement is an example of a vector

  10. Displacement along a straight line • When two displacements have the same direction, you can add their magnitudes • 4 km E + 2 km E = 6 km E 2 km 4 km 0 1 2 3 4 5 6

  11. Displacement along a straight line • When two displacements have opposite directions, you can subtract their magnitudes • 4 km E + 2 km W = 2 km E 2 km 4 km 0 1 2 3 4 5 6

  12. Displacement that is not along a straight line • When two or more vectors have different directions, they may be combined using graphing.

  13. How can we find the resultant vector?

  14. Resultant Vector • The vector sum of two or more vectors • Can be used to show total displacement • Points directly from starting point to ending point

  15. Distance v. Time Graph

  16. 11.2 Speed & Velocity Motion

  17. How do we typically measure the speed of a car?

  18. Speed • The ratio of the distance an object moves to the amount of time the object moves. • SI UNIT • Meters per second, or m/s

  19. Two types of speed • Computed for the entire duration of the trip • Speed may change from moment to moment, but this tells you the average speed over an entire trip • Measured at a particular moment in time • Example: The speedometer in a car provides instantaneous speed Average Speed Instantaneous Speed

  20. Average Speed Total Distance • Average speed = • Or • v = average speed • d = total distance traveled • t = total time Total Time d v= t

  21. Average Speed Example 1 • While traveling on vacation, you measure the times and distances you travel. You travel 35 kilometers in 0.4 hours, followed by 53 kilometers in 0.6 hours. What is your average speed? d = 35 km + 53 km = 88 km t = 0.4 h + 0.6 h = 1.0 h

  22. Average Speed Example 2 • A person jogs 4.0 km in 32 minutes, then 2.0 km in 22 minutes, and finally, 1.0 km in 16 minutes. What is the jogger’s average speed in kilometers per minute? In km/ hour?

  23. Graphing Motion • Use can use a distance-time graph to describe motion • Reminder – SLOPE • the change in the vertical axis value divided by the change in the horizontal axis value • On a distance-time graph, slope is the change in the distance divided by the change in time (or speed)

  24. Velocity • A description of both speed and direction of motion • Velocity, like displacement, is a vector because it has both magnitude and direction

  25. Combining Velocities • Two or more velocities add by vector addition • When two velocities have the same direction, you can add their magnitudes

  26. Train Example • A man on the ground observes a train passing by. Through the train windows he sees a man running in the same direction as the train is moving. What is the apparent velocity of the man running on the train if the train is moving at 30 km/h and the man is running at 5 km/h?

  27. 5 km/h 35 km/h

  28. Plane Example • A plane is moving south at 100 km/hour. Wind is blowing from the east at 25 km/ hour. What is the resultant velocity of the plane? (HINT – draw a picture to help visualize the problem)

  29. Warm-up Activity (Vector Addition)

  30. 11.3 Acceleration Motion

  31. What is acceleration? • The rate at which velocity changes • Changes in: • Speed • Direction • Or both speed & direction • Acceleration is a vector (it has both magnitude and direction)\ • SI Unit – meters per second per second (m/s2)

  32. Deceleration • An acceleration that slows an objects speed • Negative acceleration • Example • As your car approaches a red light you step on the break pedal to slow the car down. This causes the velocity of the car to change (it decreases) and thus the car decelerates.

  33. Free Fall • The movement of an object toward Earth solely because of gravity • Objects falling near Earth’s surface accelerate downward at a rate of 9.8 m/s2

  34. Free Fall (Continued) t = 0s v = 0 m/s • Each second an object is in free fall, its velocity increases downward by 9.8 m/s t = 1s v = 9.8 m/s t = 2s v = 19.6 m/s t = 3s v = 29.4 m/s

  35. Changes in Direction • You can accelerate even if your speed is constant because acceleration also includes changes in direction • Example • If you ride a bike around a curve and maintain the same speed, acceleration changes because your direction changes

  36. Roller Coasters… • Green Lantern Front Seat (Six Flags) • Describe the acceleration of the roller coaster as it reaches and just overcomes the first hill.

  37. Constant Acceleration • A steady change in velocity • The velocity of an object moving in a straight line changes at a constant rate

  38. Calculating Acceleration • For straight-line motion: Change in Velocity Acceleration = Total Time vf - vi A = t • vf= Final Velocity • vi = Initial Velocity

  39. Acceleration Example #1 t = 0s v = 0 m/s • What is the magnitude of the skydiver’s acceleration after 1 second? Between 2 and 3 seconds? t = 1s v = 9.8 m/s t = 2s v = 19.6 m/s t = 3s v = 29.4 m/s

  40. Acceleration Example #2 • A ball rolls down a ramp, starting from rest. After two seconds, its velocity is 6 m/s. What is the acceleration of the ball? vf - vi A = t

  41. vf= ? • vi = ? • t = ? vf - vi A = t

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