1.%20Use%20a%20position%20vs.%20time%20graph%20to%20interpret%20an%20object

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Today's BIG Ideas
1. Use a position vs. time graph to interpret an
objects position or displacement. 2. Define
velocity. 3. Differentiate between speed and
velocity.
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Slope is the rate of change for the object. How
far it moves in y for every x. Slope rise/run
change of y / change of x
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Position-Time Graphs
Displacement (d) or Position (p) on the y-axis
Time (t) on the x-axis
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Position-Time Graphs
What it is not
A picture of the path taken by the person or
object.
Going up?
Actual path was flat.
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Position-Time Graphs
What can a p-t graph tell you?
Instantaneous Position Position at a particular
instant (an instant lasts zero seconds).
Starting point The y-intercept tells you the
objects starting point. If an object starts at
the measuring device, then its y-intercept is 0.
If it starts 3 meters away, then its y-intercept
is 3 m.
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Position-Time Graphs
What can a p-t graph tell you?
Intersection of 2 lines tells you when 2 objects
have the same position.
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Position-Time Graphs
Dont be a dopeWhat about slope?

1. Pick two points on your line.
2. Subtract the y points.
3. Subtract the x points.
4. Divide the rise by the run.

?y
?x
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Position-Time Graphs
Slope of a p-t graph Average Velocity
?y
?d
df - di
v



?x
?t
tf - ti
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Position-Time Graphs
Now, lets look at units
The SI base unit for displacement is meters.
?y
?d

?x
?t
The SI base unit for time is seconds.
Therefore, units are m/s.
In other words, slope tells how many meters the
object (runner) moved in 1 second.
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Position-Time Graphs
The absolute value of the slope of a p-t graph
tells you the average speed (how fast the object
is moving).
Velocity is a vector Magnitude
Direction Speed is a scalar Magnitude
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Position-Time Graphs
Instantaneous Velocity the speed and direction
of an object at a particular instant.
Can be found by finding the tangent to a point on
a position-time graph.