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MOTION

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  1. MOTION

  2. Chapter Four: Motion • 4.1 Position, Speed and Velocity • 4.2 Graphs of Motion • 4.3 Acceleration

  3. Section 4.1 Learning Goals • Explain the meaning of motion. • Describe an object’s position relative to a reference point. • Use the speed formula. • Tell the difference between speed and velocity.

  4. Position is a variable given relative to an origin. • The origin is the place where position equals 0. • The position of this car at 50 cm describes where the car is relative to the track. 4.1 Position, Speed and Velocity

  5. Position and distance are similar but not the same. If the car moves a distance of 20 cm to the right, its new position will be 70 cm from its origin. 4.1 Position, Speed and Velocity Distance = 20 cm New position

  6. The variable speeddescribes how quickly something moves. To calculate the speed of a moving object divide the distance it moves by the time it takes to move. 4.1 Position, Speed and Velocity

  7. Put these are on your best friend!! Word Map

  8. The units for speed are distance units over time units. This table shows different units commonly used for speed. 4.1 Position, Speed and Velocity

  9. When you divide the total distance of a trip by the time taken you get the average speed. Total distance /Total time On this driving trip around Chicago, the car traveled and average of 100 km/h. 4.1 Average speed

  10. A speedometer shows a car’s instantaneous speed. The instantaneous speed is the actual speed an object has at any moment.(At that instance) 4.1 Instantaneous speed

  11. Solving Problems How far do you go if you drive for two hours at a speed of 100 km/h? • Looking for: • …distance • Given: • …speed = 100 km/h time = 2 h • Relationships: • d = vt • Solution: • d = 100 km/h x 2 h = 200 km = 200 km

  12. 4.1 Vectors and velocity • Position uses positive and negative numbers. • Positive numbers are for positions to the right of the origin and negative numbers are for positions to the left the origin.

  13. Speed

  14. 4.1 Vectors and velocity • Distance is either zero or a positive value.

  15. 4.1 Vectors and velocity • We use the term velocity to mean speed with direction. • (Speed +Direction= Velocity) Video

  16. 4.1 Keeping track of where you are 1 • Pathfinder is a small robot sent to explore Mars. • It landed on Mars in 1997. • Where is Pathfinder now?

  17. 4.1 Keeping track of where you are 2 • Pathfinder keeps track of its velocity vector and uses a clock. • Suppose Pathfinder moves forward at 0.2 m/s for 10 seconds. What is Pathfinder’s velocity?

  18. 4.1 Keeping track of where you are 3 • Suppose Pathfinder goes backward at 0.2 m/s for 4 seconds. What is Pathfinder’s change in position?

  19. 4.1 Keeping track of where you are 4 • The change in position is the velocity multiplied by the time.

  20. 4.1 Keeping track of where you are 5 • Each change in position is added up using positive and negative numbers. • Pathfinder has a computer to do this.

  21. 4.1 Maps and coordinates • Out on the surface of Mars, Pathfinder has more choices. • The possible directions include north, east, south, and west, and anything in between. • If Pathfinder was crawling on a straight board, it would have only two choices for direction.

  22. 4.1 Maps and coordinates • This kind of graph is called a map. • Street maps often use letters and numbers for coordinates. • A graph using north−south and east−west axes can accurately show where Pathfinder is.

  23. 4.1 Vectors on a map 1 • Suppose you run east for 10 seconds at a speed of 2 m/s. • Then you turn and run south at the same speed for 10 more seconds. • Where are you compared to where you started? • Vector Rap

  24. 4.1 Vectors on a map 2 • To get the answer, you figure out your east−west changes and your north−south changes separately. origin = (0 , 0)

  25. 4.1 Vectors on a map 3 • Your first movement has a velocity vector of +2 m/s, west-east (x-axis). • After 10 seconds your change in position is +20 meters (east on x-axis). Distance is velocity x time (d = v x t) d = 2 m/s x 10 s = +20 m

  26. 4.1 Vectors on a map 4 • Your second movement has a velocity vector of −2 m/s north−south (y-axis) • In 10 seconds you move −20 meters (south is negative on y-axis) New position = (+20 , -20) d = 2 m/s x 10 s = -20 m

  27. Solving Problems A train travels at 100 km/h heading east to reach a town in 4 hours. The train then reverses and heads west at 50 km/h for 4 hours. What is the train’s position now? • Looking for: • …train’s new position • Given: • …velocity = +100 km/h, east ; time = 4 h • …velocity = -50 km/h, west ; time = 4 h • Relationships: • change in position = velocity × time

  28. Solving Problems • Solution: • 1st change in position: • (+100 km/h) × (4 h) = +400 km • 2nd change in position: • (−50 km/h) × (4 h) = −200 km • Final position: • (+400 km) + (−200 km) = +200 km • The train is 200 km east of where it started.

  29. Chapter Four: Motion • 4.1 Position, Speed and Velocity • 4.2 Graphs of Motion • 4.3 Acceleration

  30. Section 4.2 Learning Goals • Construct and analyze graphs of position versus time, and speed versus time. • Recognize and explain how the slope of a line describes the motion of an object. • Explain the meaning of constant speed.

  31. 4.2 Graphs of Motion • Constant speed means the speed stays the same. • An object moving at a constant speed always creates a position vs. time graph that is a straight line.

  32. 4.2 Graphs of Motion • The data shows the runner took 10 seconds to run each 50-meter segment. • Because the time was the same for each segment, you know the speed was the same for each segment.

  33. 4.2 Graphs of Motion • You can use position vs. time graphs to compare the motion of different objects. • The steeper line on a position vs. time graph means a faster speed.

  34. 4.2 Slope • The slope of a line is the ratio of the “rise” to the “run”. • The steepness of a line is measured by finding its slope.

  35. 4.2 Graphs of changing motion • Objects rarely move at the same speed for a long period of time. • A speed vs. time graph is also useful for showing the motion of an object that is speeding up or slowing down.

  36. On the graph, the length is equal to the time and the height is equal to the speed. • Suppose we draw a rectangle on the speed vs. time graph between the x-axis and the line showing the speed. • The area of the rectangle is equal to its length times its height. 4.2 Graphs of changing motion Fill In graph

  37. Fill in the graphs

  38. Christopher borrowed his mother’s car to run a quick errand. Use the graph to answer questions about his trip. How far did Christopher’s car travel between points A and B? How much time did it take for Christopher to travel from point A to point B? Describe the motion of Christopher’s car between points B and C. What is the speed of the car between points A and B? Christopher’s Road Trip

  39. How would you describe the slope of the graph between points D and E? What does a negative slope tell you about the direction the car is traveling? Is Christopher traveling faster between points A and B or points F and G? How can you tell? What happens at point G?

  40. Chapter Four: Motion • 4.1 Position, Speed and Velocity • 4.2 Graphs of Motion • 4.3 Acceleration

  41. Section 4.3 Learning Goals • Define acceleration. • Determine acceleration by mathematical and graphical means. • Explain the role of acceleration in describing curved motion and objects in free fall.

  42. Key Question: What is acceleration? Investigation 4B Acceleration