8.1 The Language of Motion
 Some
common words used to
describe motion include:
–Distance
•How would you describe
–Time
the motion of the soccer
ball before and after it is
–Speed
kicked?
•What key words did you
–Position
use when describing this
situation?
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.
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 . 0 m / s
North

A scalar has no arrow.
– Example: v  5 . 0 m / s
Distance vs. Displacement

Distance (d) is a scalar that tells you how far
something has travelled.
– Example: Johnny ran a distance of 400 m

 Displacement (d)
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).
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.
Time Interval
 Time
interval or change in time is
calculated by:  t  t  t
f
i
Where: Δt = change in time (the Δ
symbol is the greek letter delta. It
means “change”.
ti = initial time
tf = final time
Example
The time interval to move
from the fire hydrant to
the sign is calculated by:
t  5 s  2 s
 3s
Displacement

Displacement or change in position is
 

calculated by: Δ d = d - d
f
i

Where: Δ d = change in position or
displacement

d i = initial position

d f = final position
Displacement and Distance
Between 2 s and 5 s, the skateboarder’s:
displacement is 5 m [E] and
distance travelled is 5 m.
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
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)
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?
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 (xaxis).

 Uniform
motion
is represented
by a straight
line on a
position-time
graph.
Positive Slope
 Slants
up to the
right.
 Indicates an object
travelling in the
positive direction
(ie: North, East, to
the right, up, etc.)
Zero Slope
 Horizontal
line.
 Indicates
that the
object is
stationary.
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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8.1 The Language of Motion