Lecture 2.3:
Graphing Motion part 1
8Th Grade Science
Ms. McKinley
Why do we need
to graph anyway?
uuuh, what’s the
point?
• VERY useful tool for
summarizing info
• show us how something
changes over a period of
time
• organize data in a visual
way
We will be learning about TWO
types of graphs. The first is…
POSITION VS. TIME GRAPHS
(SAME AS DISTANCE VS. TIME GRAPHS
Position vs. Time
graph
• Shows how an object’s
POSITION is changing over
time
• Shows how an object is
moving (away or toward the
reference point)
Position vs. Time
graph (contd.)
• UNITS
– Position has units of
distance like cm, m, and km
– Time has units like seconds,
minutes, and hours.
Video clip: Position vs. Time graph
Note: Position vs. Time graphs are THE SAME as
Distance vs. Time graphs
Slope of a Position
vs. Time graph
You’re going
the wrong way!
• SLOPE: the steepness of the
line
• The steeper the slope, the
faster the object is traveling.
• On a P vs. T graph, a steeper
line = greater average
speed.
PREGUNTA: In this position-time
graph of two turtles racing, which
turtle had the greater average
speed, the RED one or the GREEN
one?
Calculating the slope
on a Position vs. Time
graph
• The SLOPE of a P vs. T graph =
the object’s AVERAGE SPEED
slope = rise
run
RISE = change in vertical
direction
RUN = change in horizontal
direction
Let’s practice
Turtle 1
Turtle 2
• Calculate the average
speed of Turtle 1.
• Remember, the SLOPE of a
position vs. time graph is the
AVERAGE SPEED
Constant Speed on
a P vs. T graph
• A flat (not-curved) slanted
line on a P vs. T graph shows
the object is moving at a
CONSTANT SPEED.
Lecture 2.4:
Graphing Motion part 2
8Th Grade Science
Ms. McKinley
Last week we learned about…
POSITION VS. TIME GRAPHS
(SAME AS DISTANCE VS. TIME GRAPHS)
Now we will be learning about….
SPEED VS. TIME GRAPHS
Speed vs. Time
graphs
• Show how the SPEED of an
object changes over time
• CONSTANT SPEED on
a speed-time graph is
a horizontal line b/c
the speed doesn’t
change.
Speed vs. Time
graphs (contd.)
• If an object SPEEDS UP, the
line slants UP toward the right
• The object’s speed is
INCREASING.
Speed vs. Time
graphs (contd.)
• If an object slows down, the
line slants DOWN toward the
right.
• The object’s speed is
DECREASING.
OK, now let’s try it out!