The graphs above are based on the average data from our marble trials. What are the differences between these two graphs? Why do you suppose they are

Transcription

1 The graphs above are based on the average data from our marble trials. What are the differences between these two graphs? Why do you suppose they are different? What does each graph tell us about our experiment?

2 POSITION VS. TIME GRAPHS

3 DISTANCE VS DISPLACEMENT In physics when we talk about Distance we re referring to how far an object has travelled in total. When we talk about Displacement we re referring to how far an object is from where it started. For example, if you walk three blocks north to a friends house and then walk three blocks south back to your house, the DISTANCE you walked was 6 blocks. However, your DISPLACEMENT is 0 blocks because you finished where you started.

4 DETERMINING THE MOTION ON A POS. VS. TIME GRAPH Where did the object start? Which direction did it go? Where did the object stop? Is the motion uniform (constant)? Is the motion non-uniform (changing)? Can you tell which is faster? (if 2 or more objects are present)

5 READING A POSITION VS. TIME GRAPH First note that Position (x) will always be on the Y-axis (Vertical) and that Time (s) will always be on the X-axis (Horizontal). Think about each point on the line as a snapshot in time. It tells you specifically where an object was at a specific time. Don t make the mistake of thinking a Position vs Time graph is like a map showing you the actual path an object traveled. Lets practice

6 x(m) A Object A is stationary at some positive position from the origin. t(s)

7 x(m) B Object B moves away from origin with a constant positive velocity. t(s)

8 x(m) C Object C start at some positive position and moves away from the origin at a constant positive velocity. t(s)

9 x(m) Object D moves away from the origin at a constant positive velocity (slower than previous examples). D t(s)

10 x(m) Object E start at some positive position and walks toward the origin with a constant velocity. E t(s)

11 DISTANCE VS. TIME GRAPHS WITH NON- UNIFORM MOTION Changing velocity (increasing) Changing velocity (decreasing)

12 SLOPE OF A POSITION VS. T GRAPH Rise/run On a Position vs. time graph Rise = d f d i = Δd Run = t f t i = Δt Slope = Δd / Δt = Average Velocity (V avg )

13 SLOPE OF A POSITION VS TIME GRAPH

14 USING SLOPE TO PREDICT MOTION On a position vs. time graph If slope is 0, then velocity is 0. If slope is positive, velocity is constant in positive direction. If slope is negative, velocity is constant in the opposite direction. If slope is changing, velocity is changing.(i.e. you are accelerating)

15 d(m) Same velocity as C B. A V=0 B Constant +V D Slower than B or C. t(s)

16 East E A High St. B West C D

17 IN YOUR NOTEBOOK DESCRIBE THIS OBJECTS DISTANCE TRAVELED AND DISPLACEMENT. WHAT ELSE CAN WE LEARN FROM THIS POSITION VS TIME GRAPH?

18 Draw these PvT graphs in your notebook. Above each graph describe the object s speed (velocity) and direction. Assume UP is to the right and DOWN is to the left.

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21 VELOCITY-TIME GRAPHS:

22 The shape of the velocity-time graph reveals whether the object is at rest, moving at constant speed, speeding up, or slowing down.

23 Suppose an airplane has a cruising altitude of 10,600 m and travels at a constant velocity of 900 km/h [E] for 5.0 h. DATA TABLE

24 TABLE & GRAPH

25 1. SLOPE OF A VELOCITY-TIME GRAPH Just as the slope of a position-time graph reveals the rate at which position changes (velocity), the slope of a velocity-time graph reveals the rate at which velocity changes (acceleration).

26 SLOPES OF VELOCITY-TIME GRAPHS The slope of a velocity-time graph represents the acceleration of the object.

27 Non-uniform Motion riding a quad Velocity is not constant.

28 NON-UNIFORM MOTION The velocity is negative whenever the line lies in the negative region (below the x-axis) of the graph. A positive velocity means the object is moving in the positive direction A negative velocity means the object is moving in the negative direction. If a line crosses over the x-axis from the positive region to the negative region of the graph (or vice versa), then the object has changed directions.

29 V VS T AND DISPLACEMENT For velocity versus time graphs, the area bound by the line and the axes represents the displacement. 29

30 V VS T AND DISPLACEMENT The shaded area is representative of the displacement during from 0 seconds to 6 seconds. This area takes on the shape of a rectangle can be calculated using the appropriate equation. 30

31 V VS T AND DISPLACEMENT The shaded area is representative of the displacement during from 0 seconds to 4 seconds. This area takes on the shape of a triangle can be calculated using the appropriate equation. 31

32 V VS T AND DISPLACEMENT The shaded area is representative of the displacement during from 1 seconds to 3 seconds. This area takes on the shape of a trapezoid can be calculated using the appropriate equation. 32

33 Describe the motion of this object.