conceptos y practicas de movimiento relativo

1. Student Instruction Sheet 35
IT’S ALL RELATIVE
It’s All Relative
Student Instruction Sheet
Challenge
You are going to face several challenges with respect to your motion and various
frames of reference. In each of the following challenges, a different variable will
be changed or modified.
Equipment and Materials
Safety Precautions
Remember, follow the directions for using the equipment.
Background
What is your velocity right now? Perhaps surprisingly, the answer is “it depends.”
Are you being asked to describe your speed within the classroom? Your speed on a
spinning Earth? Your speed in a moving solar system traveling within a rotating
galaxy? As you can see, the question of your velocity depends on the environment
in which the motion occurs. In physics, this is referred to as “the frame of
reference.” For example, if you are sitting still in your classroom, the classroom is
your frame of reference and your velocity is zero with respect to its walls since
• Computer with USB Port • Cardstock
• PASPORT USB interface • Masking tape
• PASPORT Motion Sensor • Student Instruction Sheet
• DataStudio software • Student Response Sheet
• 1.2 m PAScar Dynamics System
• Cart Adapter Accessory
• PAScar (2)
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2. 36 Student Instruction Sheet
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you are neither approaching nor receding from them. But what if you were to get
up and walk around, or if the walls were to move? What is your velocity now within
this frame of reference?
Predict
Before beginning the eLab, complete the prediction portion of the Student
Response Sheet.
Explore
Computer Setup
1. Plug the USB interface into the computer’s USB port.
2. Plug the Motion Sensor into the USB
interface. This will automatically launch
the PASPortal window.
3. Choose the appropriate DataStudio configuration file entitled
01 Relative Motion CF.ds
Note: Configuration files automatically launch the appropriate
display(s), sampling rate(s), etc.
Equipment Setup
1. Set up and level a dynamics track with an end stop at one end of the
track.There are two ways to insure that the track is level. The first method is
to use a bubble level. The second method is to place the track on a horizontal
surface. Level the track by placing the PAScar on the track. If the cart rolls
one ways or the other, use the leveling screw at one end of the track to raise
or lower that end until the track is level and the cart does not roll one way or
the other.
2. Connect a PASPORT Motion Sensor to a PAScar using
the Cart Adapter Accessory. Set the ‘range select
switch’ on the top of the Motion Sensor to the Cart
icon (short range).
3. The cart with the Motion Sensor represents you and
will be referred to as PAScar #1.
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3. Student Instruction Sheet 37
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4. Place the card stock onto the second car by pushing the card into the slots on
top of the PAScar. This car will be referred to as PAScar #2.
Note: Insure that the gold disc is pointing directly at the card stock target.
5. Place PAScar #2, with the card stock, at the end stop on the track.
6. Place PAScar #1, with the Motion Sensor attached, at the other end of the
track.
7. Set the plunger on PAScar #2 at the first, i.e. lowest, setting and place the
plunger against the end stop. Try a few practice launches to make sure that
you can release the cart smoothly.
Note: For all the investigations in this lab, position the cord
from the sensor so that the cart can move freely. It may be
necessary for you or a lab partner to hold up the cord so that it
doesn’t drag on the track or the lab bench.
Record Data
1. To collect data, click the Start ( ) button and then quickly release
the plunger.
2. Just before the two carts collide press the Stop ( ) button.
Challenge #1
PAScar #2
card stock
}
Motion Sensor
End Stop
level dynamic track
PAScar
#1
(YOU!)
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3. Examine your graph.
Hint: if the graph appears very “spikey” or the graph appears
counterintuitive in terms of the classes earlier discussion of
the four scenarios, try running the PAScar at a slower velocity
until the graph becomes smoother in appearance.
4. Using the Smart Tool ( ) along with the Statistics Pull Down Menu
Button ( ), complete Challenge #1 on your Student Response Sheet:
5. Repeat your data collection several times to insure consistency.
Ch
In the previous investigation, you were stationary relative to a moving car. In this
investigation, both cars will be in motion towards each other. Reset the cars as
described in the Equipment Setup.
1. Click the Start button. Release the plunger and approximately a half second
later gently push PAScar #1 towards PAScar #2 (you). Click the Stop button
just before the collision.
2. Using the Smart Tool the Statistics Pull Down Menu Button, determine the
relative velocity of PAScar #2 with respect to PAScar #1. Record this value
on the Student Response Sheet.
3. Carefully examine your graph. Reflect on the motion represented by these
lines.
Clue: Remember the Hint from Challenge #1.
4. Complete Challenge #2 portion on your Student Response Sheet.
5. Repeat your data collection several times to insure consistency.
Challenge #2
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5. Student Instruction Sheet 39
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1. Set up the PAScars as you did for the previous investigation, but place PAScar
#1 40-50 cm from the end stop of the track.
2. Click the Start button, and then release the plunger on PAScar #2.
Approximately a half second later, push PAScar #1 away from PAScar #2.
Click Stop to end data recording.
3. Once again, using the Smart Tool and the Statistics Pull Down Menu Button,
complete Challenge #3 portion on your Student Response Sheet.
4. Repeat your data collection several times to insure consistency.
1. What would the relative velocity of PAScar #2 be in relationship to you if you
were both moving away from each other? Place the end stop in the center of
the track. Set the plunger of each PAScar to the first setting. Place one
PAScar on each side of the end stop with the plunger touching the end stop.
2. Click the Start button. Release the plunger on PAScar #2. Approximately one
half second later, release the plunger on PAScar #1. Click the Stop button
just before the carts reach the ends of the track.
3. Repeat your data collection several times to insure consistency.
Analyze
1. Save your DataStudio file (on the File menu, click Save Activity As...) to the
location specified by your teacher.
2. Answer the questions and define the vocabulary words on the Student
Response Sheet.
3. Follow your teacher’s instructions regarding cleaning up your work space.
Challenge #3
Going Further: Challenge #4
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7. Student Response Sheet 49
IT’S ALL RELATIVE
Student Response Sheet
It’s All Relative
Vocabulary
Use available resources to find the definitions of the following terms:
frame of reference: ___________________________________________
___________________________________________________________
relative motion: _______________________________________________
___________________________________________________________
relative velocity: ______________________________________________
___________________________________________________________
speed: ______________________________________________________
___________________________________________________________
velocity: ____________________________________________________
___________________________________________________________
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Predict
1. What do you think the graph of velocity vs. time of a moving cart relative to
your stationary position will look like? Sketch your prediction.
2. What do you think the graph of velocity vs. time of a moving cart will look like
if you, the observer, on the PAScar with a Motion Sensor mounted on it is in
motion toward the other moving cart? Sketch your prediction.
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Data
From your graphs, determine the following:
1. Based on your graphical results in Challenge #1, do you see a pattern? For
instance, are there distinct and repeatable segments for each run? If so, how
many segments do you observe?
___________________________________________________________
___________________________________________________________
___________________________________________________________
2. Describe what your observations represent in terms of velocity, relative
velocity and frame of reference.
___________________________________________________________
___________________________________________________________
___________________________________________________________
3. What does the negative sign tell you about the motion?
___________________________________________________________
___________________________________________________________
Average velocity
relative to PAScar #1
after launch
Average velocity
Rrelative to the ground
after launch
Trial 1
Trial 2
Trial 3
Average
Challenge #1
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4. Based on your graphical results in Challenge #2, do you see a pattern? For
instance, are there distinct and repeatable segments for each run? If so, how
many segments do you observe?
___________________________________________________________
___________________________________________________________
5. Describe what your observations represent in terms of velocity, relative
velocity and frame of reference.
___________________________________________________________
___________________________________________________________
Average velocity of
PAScar #2 relative to
the Motion Sensor as
both carts are moving
Average velocity
of PAScar #2 relative to the
ground
Trial 1
Trial 2
Trial 3
Average
Challenge #2
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11. Student Response Sheet 53
IT’S ALL RELATIVE
6. Based on your graphical results in Challenge #3, do you see a pattern? For
instance, are there distinct and repeatable segments for each run? If so, how
many segments do you observe?
___________________________________________________________
___________________________________________________________
7. Describe what your observations represent in terms of velocity, relative
velocity and frame of reference.
___________________________________________________________
___________________________________________________________
Average velocity of
PAScar #2 relative to
the Motion Sensor as
both carts are moving
Average velocity
of PAScar #2 relative to the
ground
Trial 1
Trial 2
Trial 3
Average
Challenge #3
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8. Based on your graphical results in Challenge #4, do you see a pattern? For
instance, are there distinct and repeatable segments for each run? If so, how
many segments do you observe?
___________________________________________________________
___________________________________________________________
9. Describe what your observations represent in terms of velocity, relative
velocity and frame of reference.
___________________________________________________________
___________________________________________________________
Average velocity of
PAScar #2 relative to
the Motion Sensor as
both carts are moving
Average velocity
of PAScar #2 relative to the
ground
Trial 1
Trial 2
Trial 3
Average
Challenge #4
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13. Student Response Sheet 55
IT’S ALL RELATIVE
Synthesize
1. If you are an observer standing still, what can you say about the relative
velocity of a art moving toward you? Away from you?
___________________________________________________________
___________________________________________________________
2. If you are an observer moving at 3.2 m/s towards an object that is moving
toward you at 1.4 m/s, what is the relative velocity of the object moving
toward you?
___________________________________________________________
___________________________________________________________
3. Explain the answer from the previous question.
___________________________________________________________
___________________________________________________________
4. Summarize the positive and negative values of velocity relative to the Motion
Sensor.
___________________________________________________________
___________________________________________________________
5. How would you explain “relative velocity” to someone who is not in your physics
class?
___________________________________________________________
___________________________________________________________
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