Particle Moving with Constant Velocity Model
Key ideas:
By the end of this unit, you should be able to do the following:
1. You should be able to determine the average velocity of an object in two ways:
determining the slope of an x vs. t graph.
using the equation
2. You should be able to determine the displacement of an object in two ways:
finding the area under a v vs. t graph.
using the equation
3. Given an x vs. t graph,
describe the motion of the object (starting position, direction of motion, velocity)
draw the corresponding v vs. t graph
draw a motion map for the object.
determine the average velocity of the object (slope).
write the mathematical model which describes the motion.
4. Given a v vs. t graph,
describe the motion of the object (direction of motion, how fast)
draw the corresponding x vs. t graph
determine the displacement of the object (area under curve).
draw a motion map for the object.
write a mathematical model to describe the motion.
Terms and Definitions:
Average Velocity = Slope of x-t graph =
Change in Position x f " x i
=
Change in Time
t f " ti
Δx = change in position = xf - xi = displacement = area under v-t graph. Displacement is the straightline distance between the starting point and the ending point. Displacement also reports the direction of
!
motion.
Odometer reading = total distance traveled along a path to get from the starting position to the ending
position.
Average Speed = Distance along path / Change in Time
Scalar = A Quantity that tells "how much" only i.e. speed, time, mass, odometer reading . . .
Vector = A quantity that tells how much and which direction i.e. velocity, displacement, force . . .
Qualitative = Conceptually correct, but not numerically precise
Quantitative = Numerically Accurate
©Modeling Instruction 2010
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U2 Constant Velocity - Key Ideas v3.0
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Date
Pd
Constant Velocity Particle Model Worksheet 1:
Motion Maps and Position vs. Time Graphs
1. Given the following position vs. time graph, draw a motion map with one dot for each second.
Position vs. Time
4
3
0m
2
5m
+
1
0
0 1
2 3 4 5 6
time (seconds)
7 8
Describe the motion of the object in words:
2. Given the following motion map, where positions have been recorded with one dot each second,
draw a position vs. time graph.
Position vs. Time
0m
5m
+
time (seconds)
Describe the motion of the object in words:
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3. Consider the position vs. time graph below for cyclists A and B.
a. Do the cyclists start at the same point? How do you know? If not, which is ahead?
b. At t= 7s, which cyclist is ahead? How do you know?
c. Which cyclist is traveling faster at 3s? How do you know?
d. Are their velocities equal at any time? How do you know?
e. What is happening at the intersection of lines A and B?
f. Draw a motion map for cyclists A and B.
0m
+
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4. Consider the new position vs. time graph below for cyclists A and B.
a. How does the motion of the cyclist A in this graph compare to that of A in question 3?
b. How does the motion of cyclist B in this graph compare to that of B in question 3?
c. Which cyclist has the greater speed? How do you know?
d. Describe what is happening at the intersection of lines A and B.
e. Which cyclist has traveled further during the first 5 seconds? How do you know?
f. Draw a motion map for cyclists A and B.
0m
+
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5. To rank the following, you may need to look at the key ideas sheet for the difference between
displacement and odometer reading.
A
x (m)
B
x (m)
C
x (m)
25
10
5
0
x (m)
10
0
10 t (s)
0
D
x (m)
0
10 t (s)
0
E
10 t (s)
0
F
x (m)
10
15
5
3
0
0
10 t (s)
0
10 t (s)
0
0
0
3
10 t (s)
a. Rank the graphs according to which show the greatest displacement from the beginning to the
end of the motion.
Most positive  1______ 2______ 3______ 4______ 5______ 6______  Most negative
Explain your reasoning for your ranking:
b. Rank the graphs according to which show the greatest odometer reading from the beginning
to the end of the motion.
Greatest 1________ 2________ 3________ 4________ 5________ 6________ Least
Explain your reasoning for your ranking:
©Modeling Instruction 2010
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U2 Constant Velocity ws 1 v3.0
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Date
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Constant Velocity Particle Model Worksheet 2:
Motion Maps and Velocity vs. Time Graphs
Sketch velocity vs. time graphs and motion maps corresponding to the following descriptions of the
motion of an object.
1. The object is moving in the positive direction at
a constant (steady) speed.
Motion Map:
0m
+
time
2. The object is standing still.
Motion Map:
0m
+
time
3. The object moves in the negative direction at a
steady speed for 10s, then stands still for 10s.
Motion Map:
0m
+
time
4. The object moves in the positive direction at a
steady speed for 10s, reverses direction and
moves back toward the negative direction at
the same speed.
Motion Map:
0m
time
+
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U2 Constant Velocity - ws 2 v3.0
Draw the velocity vs time graphs for an object whose motion produced the position vs time graphs
shown below at left.
5.
6.
7.
8. For many graphs, both the slope of the line and the area between the line and the horizontal axis
have physical meanings.
a. What does the slope of a position time graph tell you about the motion of an object?
b. Looking at the velocity time graphs, determine the units for a square of area on the graph.
c. What does the area under the velocity-time graph tell you about the motion of an object?
©Modeling Instruction 2010
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U2 Constant Velocity - ws 2 v3.0
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Date
Pd
Constant Velocity Particle Model Worksheet 3:
Position vs. Time and Velocity vs. Time Graphs
1. Robin, rollerskating down a marked sidewalk, was observed at the following positions at the
times listed below:
t (s)
x (m)
0.0
10.0
1.0
12.0
2.0
14.0
5.0
20.0
8.0
26.0
10.0
30.0
t (s)
a. Plot a position vs. time graph for the skater.
b. Explain how you can use the graph to determine how far he was from the origin at t = 6s.
c. Write a mathematical model that describes the skater's motion.
d. Was his speed constant over the entire interval? How do you know?
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2. In a second trial, the timer started her watch a bit sooner. The following data were obtained:
t (s)
x (m)
0.0
4.0
2.0
10.0
4.0
16.0
6.0
22.0
8.0
28.0
10.0
34.0
t (s)
a. Plot the position vs. time graph for the skater.
b. How far from the origin was the skater at t = 5s? How do you know?
c. Was the skater’s speed constant? If so, what was it?
d. In the first trial, the skater was further along at 2s than he was in the second trial. Does this mean
that he was going faster? Explain your answer.
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3. Suppose now that our skater was observed in a third trial. The following data were obtained:
t (s)
0.0
2.0
4.0
6.0
8.0
10.0
12.0
14.0
16.0
x (m)
0.0
2.0
4.0
4.0
3.0
2.0
2.0
5.0
8.0
t (s)
a. Plot the position vs. time graph for the skater.
b. What do you think is happening during the time interval: t = 4s to t = 6s? How do you know?
c. What do you think is happening during the time interval: t = 6s to t = 10s? How do you know?
d. Determine the skater's average velocity from t = 0s to t = 16s. (Average velocity is the
displacement (final position minus initial position) divided by time elapsed.)
e. Determine the skater's average speed from t = 0s to t = 16s. (Average speed is the distance
traveled along the path (change in odometer reading) divided by time elapsed.)
f. In what situation is average speed a better measure of motion than average velocity?
g. In what situation is average velocity a better measure of motion than average speed?
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4. Rank the following:
A
x (m)
B
x (m)
C
x (m)
25
10
5
0
x (m)
10
0
10 t (s)
0
D
x (m)
0
10 t (s)
0
E
10 t (s)
0
F
x (m)
10
15
5
3
0
0
10 t (s)
0
10 t (s)
0
0
0
3
10 t (s)
a. Rank the graphs according to which show the greatest average velocity from the beginning to
the end of the motion. (Zero is greater than negative, and ties are possible.)
Most pos. v 1________ 2________ 3________ 4________ 5________ 6________ Most neg. v
Explain your reasoning for your ranking:
b. Rank the graphs according to which show the greatest average speed from the beginning to
the end of the motion.
Greatest 1________ 2________ 3________ 4________ 5________ 6________ Least
Explain your reasoning for your ranking:
©Modeling Instruction 2010
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U2 Constant Velocity - ws3 v3.1
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Date
Pd
Constant Velocity Model Worksheet 4:
Velocity vs. Time Graphs and Displacement
1. This motion map shows the position of an object once every second. From the motion map,
answer the following:
a. Describe the motion of the object.
b. Represent the motion with a
quantitative x vs. t graph.
c. Represent the motion with a
quantitative v vs. t graph.
x
v
t
t
d. Write a mathematical expression that represents the relationship between position and time.
e. Write a mathematical expression that represents the relationship between velocity and time.
f. Cross hatch the area under the velocity-time graph. What are the units of this area? Describe what
the area under the v-t graph represents and find its value.
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U2 Constant Velocity - ws4 v3.0
2. From the position vs. time data below, answer the following questions.
a. Construct a graph of position vs. time.
b. Construct a graph of velocity vs. time.
t (s)
0
1
2
3
4
5
6
7
8
9
x (m)
0
2
4
4
7
10
10
10
5
0
c. Draw a motion map for the object.
0m
+
d. Determine the displacement from t = 3.0s to 5.0s using the velocity vs. time graph.
e. Determine the displacement from t = 7.0 s to 9.0 s using the velocity vs. time graph.
f. Determine the average velocity from t = 4 s to 8 s.
g. Determine the average speed from t = 4 s to 8 s.
©Modeling Instruction 2010
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U2 Constant Velocity - ws4 v3.0
3. In the following situations, a passenger is throwing a baseball on a moving train. Rank the
baseball’s speed and velocity relative to the ground. Motion to the left is negative and to the right
is positive.
A
C
B
3 m/s
6 m/s
D
10 m/s
4 m/s
3 m/s
7 m/s
2 m/s
5 m/s
6 m/s
F
E
3 m/s
5 m/s
5 m/s
a. Most pos. velocity  ______ ______ ______ ______ ______ ______  most neg. velocity
b. Fastest speed  ______ ______ ______ ______ ______ ______  slowest speed
c. What is the difference between speed and velocity?
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Constant velocity extension (relativity):
4. In the following situation, the person holds a laser. A pulse of light emerges from the laser at the
speed of light, c. Our train (or spaceship) now travels at half the speed of light.
A
B
v=c
v=c
v = 0.5 c
v = 0.5 c
a. How fast does the light pulse travel away from the person on the train in situations A and B?
Explain your reason for your answer.
b. How fast does the light pulse travel relative to the ground in situations A and B?
Explain your reason for your answer.
c. Does the speed of light
i. depend upon the motion of the light source relative to the observer?
If so, can we say that the speed of light is a constant?
ii. remain constant, regardless of the motion of the light source to the observer?
If so, how can the speed of the light pulse relative to the person in the train and
relative the person on the ground be reconciled?
©Modeling Instruction 2010
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U2 Constant Velocity - ws4 v3.0
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Date
Pd
Constant Velocity Particle Model Worksheet 4:
Multiple Representations of Motion
Given one motion representation, supply the missing motion representations.
1.
Written description:
x
t
v
Motion map:
t
2.
Written description:
x
t
v
Motion map:
t
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3.
Written description:
x
3
6
8
t (s)
v
Motion map:
t
4.
Written description:
x
t
+2
v
(m/s)
-1
Motion map:
2
4
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8 t (s)
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5.
Written description:
x
Object moves with constant positive velocity
for 4 seconds. Then, it stops for 2 seconds
and returns to the initial position in 2
seconds.
t
v
Motion map:
t
6.
Written description:
x
t
v
Motion map: ∆t = 1 s
t
©Modeling Instruction 2010
0m 1m
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U2 Constant Velocity - ws5 v3.0
7.
Written description:
x
Object A starts 10m to the right of the
origin and moves to the left at 2 m/s.
Object B starts at the origin and moves to
the right at 3 m/s.
t
v
Motion map:
t
8.
Written description:
x
t
v
Motion map: ∆t = 1s
t
©Modeling Instruction 2010
3m
4m
A
B
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U2 Constant Velocity - ws5 v3.0