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# describing motion

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Introductory lesson on describing motion for the 9th grader.

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### describing motion

1. 1. Describing Motion Chapter 2: section 1 Tuesday 9/26/13
2. 2. 2 Goals for this lesson 1. Describe motion 2. Perform calculations to determine speed
3. 3. Motion and Position • A reference point is needed to determine the position of an object • Motion occurs when an object changes its position relative to a reference point – Ex: How do people in a car know they are moving? – Ex: Throw a ball, how do you know it moved
4. 4. Distance vs Displacement • Distance - how far an object has moved – meter (m) – Ex: It takes 4 laps around a 400m track to make approximately a 1 mile race. What is the total distance in meters? • Displacement – the distance and direction of an object relative to the starting point – Ex: a person walks 20 m North, turns walks 10 m West, and then 20 m South, What is the displacement?
5. 5. Speed • • • • • Speed = s Distance = d Time = t Most common unit = meters per second (m/s) speed=Total distance traveled ÷ total time Distance Speed Time • This picture will help with solving problems mathematically without knowing Algebra!!
6. 6. Practice problems 1. A passenger elevator travels from the first floor to the 60th floor, a distance of 210 m, in 35 sec. What is the elevator’s speed? 2. How far does a car travel in 0.75 hours if it is moving at a constant speed of 88 km/hour? 3. A motorcycle is moving at a constant speed of 40 km/h. How long does it take to travel 10 km?
7. 7. Homework Speed worksheet Tomorrow – Motion detector lab
8. 8. Monday 9/30/13 • Pick up – 9.30 Reinforcement section 1
9. 9. Goals for the lesson 1. Define speed terms 2. Interpret a position time graph 3. Perform calculations to determine velocity
10. 10. Opener for Monday 9/30/13 1. Describe how the skier’s velocity changes during the race. 2. Why does the skier’s velocity increase as he races downhill? 3. How does being in a tuck position affect a skier’s motion?
11. 11. Speed Terms • Constant speed – if you maintain the same speed over a time interval • Changing speed – speed up or slow down over a time interval • Average speed - describes the speed of motion when speed is changing • Instantaneous speed – the speed at a given point in time
12. 12. Graphing Motion • Time is plotted on the x axis • Distance traveled is plotted on the y axis • Slope of a distance-time graph = velocity (speed) – Steeper line = faster – Horizontal line = not moving, no speed • Connect the dots with a straight “best fit” line not a dot-to-dot line – Easier to extrapolate data in between points
13. 13. Position (m) Interpreting a graph • When is the object stopped? How do you know? • When is it moving the fastest? slowest? Explain
14. 14. Velocity • • • • Velocity symbol = v Displacement = x Time = t Includes the speed of an object but also the direction of its motion. • displacement ÷ total time = velocity Displacement Velocity Time
15. 15. Homework • Reinforcement sec 1 • Quiz Wednesday – speed and velocity calculations – interpreting graphs – describing motion