Motion Graphs Lecture 3
Video14. Bill Nye: Motion
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Motion & Graphs
• Motion graphs are an important tool used to
show the relationships between position, speed,
and time.
• It’s an easy way to see how speed or position
changes over time
• These types of graphs are called kinematic
graphs.
• There are two types:
– Position vs. Time graphs
– Speed vs. Time Graphs
Video15. Graphing Motion
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Position Vs. Time
• Used to show an
object’s position at
a given time.
• Position: on y-axis
• Time: on x-axis
You Try It: Graphing
Position Vs. Time
• Suppose you are helping a
friend who is training for a
track meet.
• She wants to know if she is
running at constant speed.
• You mark the track in 50-meter
increments and measure her
time at each position during a
practice run.
• Create a position-time graph
using her data.
Time (s)
Position (m)
0
0
10
50
20
100
30
150
You Try It: Graphing
Position Vs. Time
•
When you’ve plotted all 4
points, you should get a
graph that looks like this…
What would her speed be?
•
–
Time (s)
Position (m)
0
0
10
50
20
100
30
150
Choose any point, & divide
distance (position) over time
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You Try It: Graphing
Position Vs. Time
• What would her speed be?
– 50m/10s = 5 m/s
– 100m/20s = 5 m/s
• Notice that this is a straight line
- why??
– She is moving at a constant
speed - neither slowing down nor
accelerating
You Try It: Graphing
Position Vs. Time #2
•
Graph the motion of this car.
•
•
Graph the points: (0,0), (1, 10), (2, 20), (3, 30), (4, 40), (5, 50).
Your graph should look like this…
•
What is this car’s velocity?
–
A constant 10 m/s
Video16. Position vs Time
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What does slope
have to do with it?
• Slope is the ratio of the
rise (y-axis) to the run
(x-axis) of a line on a
graph.
• A bigger slope means a
steeper line which
means a faster speed.
Steeper Line = Faster Speed
Steeper Line = Faster Speed
Negative Slopes
• What does this graph mean???
• And this one?
• They show an object that is
slowing down - or
decelerating.
• The first graph is slowly
decelerating, while the second
graph is quickly decelerating.
Basically…
You might want to draw this
graph in your Motion Math
Little book
This is another really good graph to draw in your
motion math little book
Video 17. Distance,
Velocity & Acceleration
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Position Vs. Time Changing Velocity
• Now consider a car that has a changing velocity.
• It is not moving at a constant rate, but getting
faster by the second.
• What would this graph look like?
• You try it first…
Does your graph look like this?
Be sure you have this one drawn
You Try It:
GrAPHING
Position Vs. Time #3
• What would the graph look like for a car
that traveled 10 m in the 1st second,
15 m by the 2nd second,
25 by the 3rd second,
and 40 m by the 4th second?
Predict: What does
THIS GRAPH show?
• This graph is for a car
moving with a constant
velocity of +5 m/s for 5
seconds, stopping abruptly,
and then remaining at rest
for 5 seconds.
• The straight line means its
position is NOT changing.
Speed Vs. Time
• Used to show an
object’s speed at a
given time.
• Speed: on y-axis
• Time: on x-axis
Speed Vs. Time Constant Speed
• This graph shows the speed
versus time for a ball rolling
at constant speed on a level
floor.
• On a speed vs. time graph,
constant speed is shown
with a straight horizontal
line.
• If you look at the speed on
the y-axis, you see that the
ball is moving at 1 m/s for
the entire 10 seconds.
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Speed Vs. Time Constant Speed
• Compare this speed-time graph to the position-time
graph for the ball.
• Both of the graphs show the exact same motion, even
though they look different.
• If you calculate the slope of the lower graph, you will
find that it is still 1 m/s.
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You Try It: Graphing
Speed Position Vs. Time
• Maria walks at a constant speed of 6 m/s for 5 seconds.
• Then, she runs at a constant speed of 10 m/s for 5 seconds.
• Create a speed-time graph using her data.
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Speed Vs. Time Changing Speed
• As we know, most objects don’t
move at a constant speed.
• If a speed vs. time graph slopes
up, then the speed is increasing.
• If it slopes down, then the speed is
decreasing.
• If the graph is horizontal, then the
object is moving at a constant
speed.
YOU MAY WANT TO DRAW
THESE GRAPHS TOO!
Putting it All Together
1. Which runner won the
race?
–
Albert won the race. He
reached 100 meters first.
2. Which runner stopped for
a rest?
–
Charlie stopped for a rest
at 50m.
3. How long did he stop for?
–
Charlie stopped for 5
seconds. (13-8)
Putting it All Together
4. How long did Bob take to
complete the race?
–
Bob finished the race in 14
seconds
5. Calculate Albert's average
speed.
–
–
–
Speed = distance/time
Speed = 100m/12s =
Albert’s Speed = 8.3 m/s
Video 18.
PUTTING IT ALL TOGETHER
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