```• 8.1 The Language of Motion
Pages 344 – 361
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8.1 The Language of Motion
• Some common words used to describe motion
include:
 Distance
 Time
 Speed
•How would you describe
the motion of the soccer
 Position
ball before and after it is
kicked?
•What key words did you
use when describing this
situation?
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Direction Makes a Difference
• Two main types of quantities:
Scalars: Describe magnitude
but not direction. (Magnitude is
the size of a measurement)
 Example: Johnny walked 25
km
Vectors: Describe magnitude
and direction.
 Example: Johnny walked 25
km North
Every time you use a map
or give directions, you are
using vectors.
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Vectors vs Scalars
• You can always tell if a quantity is a vector
because there will be an arrow drawn above
it.

 Example: v  5.0m / s North
• A scalar has no arrow.
 Example:
v  5.0m / s
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Distance and Displacement
• Distance (d) is a scalar that tells you how far
something has travelled.
 Example: Johnny ran a distance of 400 m

• Displacement ( d ) is a vector that describes your
position relative to where you started.
 Example: Johnny ran 400 m North of his home.
• We measure both distance and displacement in
metres (m).
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Example
A car leaves home and drives 10 km to the store
and then returns home. The car has driven a
total distance of 20 km but its final displacement
is 0 km.
Grover can teach us the difference too!
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Time Interval
• Time interval or change in time is calculated by:
t  t f  ti
Where: Δt = change in time (the Δ symbol is the greek
letter delta. It means “change”.
ti = initial time
tf = final time
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The time interval
to move from the
fire hydrant to the
sign is calculated
by:
t  5 s  2 s  3 s
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Displacement
• Displacement or change in position is calculated
  
by:
d = df - di

Where:
 d = change in position or displacement
d i = initial position

df = final position
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Displacement and Distance
Between 2 s and 5 s, the
skateboarder’s:
displacement is 5 m [E].
distance travelled is 5 m.
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Watch for Signs
Turn to page 349 for common sign conventions
Copy Figure 8.8 into notes
Turn to page 352 in textbook and do Activity 8-1B
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Uniform Motion
• Uniform motion is a term that describes objects
that do not speed up, slow down, or change
direction.
• In other words, they travel at constant
velocities (we will discuss velocity more later)
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Uniform Motion Example
The position of the ball in this photo is
shown at equal time intervals. How would
you determine if this motion is uniform
motion?
What would the picture look like if the ball
was NOT in uniform motion?
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Graphing Uniform Motion
• Motion of an object
can be analyzed by
drawing a positiontime graph.
• A position-time graph
plots position data on
the vertical axis
(y-axis) and time data
on the horizontal axis
(x-axis).
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• Uniform motion is
represented by a
straight line on a
position-time graph.
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Positive Slope
• Positive slope
 Slants up to the
right.
 Indicates an object
travelling in the
positive direction
(ie: North, East, to
the right, up, etc.)
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Zero Slope
• Zero slope
 Horizontal line.
 Indicates that
the object is
stationary.
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Negative Slope
• Negative slope
 Slants down
to the right.
• Indicates an
object
travelling in the
negative
direction (ie:
South, West, to
the left, down,
etc.)
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Homework
• Complete questions 1 – 17 on page 361 in full
sentences.
• Expect a short quiz at the beginning of next class.
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