… by comparing the momenta before and after and by the percentage differences you calculated. Do you find momentum conserved best for any particular kind of collision?Next, list the sources of experimental error, explaining each in a sentence or two, and try to estimate how large an error it would introduce in the measured values you obtained. Consider for example what happens in a collision whether the two gliders really interact only with each other or have other interactions and effects you see or hear. You can also consider the model itself. What aspects of the simulation are inaccurate and may have contributed to error?Include in this analysis how the error would change your results. Would the calculated momentum be higher or lower due to the types of error you found?
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Science | Laboratory Instructions | Laboratory: Momentum
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Laboratory Instructions
Laboratory: Momentum
Materials
Supplied




Student Guide
Laboratory Guidelines
Threaded Discussion Board Grading Rubric
PHX 1.05 LRD: Momentum
Notes
Timers
The timer starts when it is blocked by a glider and stops when it is unblocked. So the timer records the total time
the photogate was blocked. The top timer records the first pass, and the bottom records the second pass, or the
pass of another glider. Once the bottom timer has recorded data and you’ve copied that data into the tables in the
Lab Report for Discussion (LRD), you need to press the reset button on top of the photogate to record new data.
Air Track
Don’t forget to turn on the air track using the switch on the air compressor before you perform a trial. When the
trial is done, turn off the air track to restore friction and cause the gliders to stop moving.
The air track should be assigned a positive and negative end for your calculations. It doesn’t matter what side is
positive and what side is negative, but for this experiment use left side as negative and the right side as positive
for your calculations.
Data Workbook
The virtual lab has a data workbook to record your data. Clicking the save button will save your data to the
workbook. However, after a successful trial, you should always record the data in the LRD. It’s easier to keep
track of there, and it’s a good idea to have a hard copy of your data.
Glider Length
The yellow glider is .0765 m long, and the red glider is .1509 m long. Record this information in the data table in
the LRD.
Advance Prep (3 days)
Review the list of materials for the lab prior to the lesson, because there are several items that you must supply.
Safety
Review the Laboratory Guidelines before conducting the lab.
Experiment
Setup
1. Note that the left side of the track is negative and the right side is positive for your calculations.
2. Print or open the LRD for data collection. You may record data in the virtual lab’s data workbook, but you will
need to copy it to the LRD at some point for analysis.
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Page 1 of 5
Science | Laboratory Instructions | Laboratory: Momentum
3. Record the mass and length of each glider in the data table in the LRD. Remember to convert the mass to kg.
4. Experiment with different setups to get good data. You will have to repeat the experiment and may need to
practice positioning gliders and choosing the glider push. Also, the gliders should only collide once. So
sometimes you will have to catch a glider that has already gone through a gate. You don’t want a glider to
bounce into another glider that has not gone through a gate, and you do not want gliders bouncing back into
each other giving additional velocity to the other glider.
5. Don’t assume that both gliders have to move or that they will both bounce off each other and go back through
the gates. You may decide not to push a glider, or you may find that after one glider hits another, it doesn’t
bounce backwards. If a glider stops moving after a collision, record that as a zero final velocity. If you cannot
get accurate data for a certain trial, don’t record the data. Just do another trial with a slightly different setup.
Elastic Collision Procedure
Tell your virtual lab partner you want to perform an elastic collision. He or she will slide the magnet to the nonfacing ends of the gliders so the gliders will bounce off each other when they collide. For this lab, it doesn’t matter
how hard you push the gliders, you just need to make sure they collide in the center of the track.
The top timers record the photogate the glider is blocked. The bottom timers record the second time the
photogate is blocked. Because we established the left side of the track as negative and the right side as positive,
gliders moving toward the right are moving in a positive ( + ) direction and gliders moving toward the left are
moving in a negative ( − ) direction.
Perform three different elastic collision setups and record the data in the tables in the LRD. You may need to run
multiple trials to get good data, but you only need to record the final data in your report. Calculate the velocity of
the gliders using the formula v = d/t where d is the distance the glider moved while it blocked the photogate, which
is equal to the length of card on top of the glider. Calculate the momentum of the glider using the formula p = mv.
Make sure you reset the photogates after each trial, and make sure the air track is running before you perform a
trial.
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Page 2 of 5
Science | Laboratory Instructions | Laboratory: Momentum
Elastic Collision Air Track Data: Sample Data
Criteria
Time (s)
Direction ( + / − )
Red (larger) glider
before collision
0.54
+
Yellow (smaller)
glider before
collision
0.11

Total momentum
before collision
cell s haded
cell s haded
Red (larger) glider
after collision
0.41

Yellow (smaller)
glider after
collision
0.13
+
cell s haded
cell s haded
Total momentum
after collision
Velocity (m / s)
Momentum (kg • m / s)
cell s haded
cell s haded
Inelastic Collision Procedure
Tell your virtual lab partner you want to perform an inelastic collision. He or she will slide the magnet to the facing
ends of the gliders so the gliders will stick to each other when they collide. For this lab, it doesn’t matter how hard
you push them, you just need to make sure they collide in the center of the track.
There are a number of ways to create an inelastic collision, but starting with one of the gliders standing still is the
simplest. Place the yellow glider in the center of the track and choose “No push” for your partner. Because the
yellow glider is not moving, you know its initial speed is zero m/s.
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Science | Laboratory Instructions | Laboratory: Momentum
Note: When you move the glider past the photogate, it will trigger the timer. Make sure to reset the timer before
starting the experiment.
Because there is a gap between the glider cars, the top timer on the left will record the yellow glider time, and the
bottom timer will record the red glider time. You don’t need both of these in your calculations when the gliders are
attached together. The yellow glider has a shorter time because it is smaller, but both gliders are traveling as one
object at the same velocity.
The top timers record the first time a glider blocked the photogate. The bottom timers record the second time the
photogate is blocked. Because we established the left side of the track as negative and the right side as positive,
gliders moving toward the right are moving in a positive ( + ) direction and gliders moving toward the left are
moving in a negative ( − ) direction.
Perform three different inelastic collision setups and record the data in the tables in the LRD. You may need to
run multiple trials to get good data, but you only need to record the final data in your report. Calculate the velocity
of the gliders using the formula v = d/t, where d is the distance the glider moved while it blocked the photogate,
which is equal to the length of the card on top of the glider. Calculate the momentum of the glider using the
formula p = mv. For final momentum, don’t forget to use the combined mass of both gliders.
Make sure you reset the photogates after each trial, and make sure the air track is running before you perform a
trial.
Inelastic Collision Air Track Data: Sample Data
Criteria
Time (s)
Direction ( + / − )
Red (larger) glider
before collision
0.16

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Velocity (m / s)
Momentum (kg • m / s)
Page 4 of 5
Science | Laboratory Instructions | Laboratory: Momentum
Criteria
Time (s)
Direction ( + / − )
Yellow (smaller)
glider before
collision
not moving
not moving
0.12 (yellow glider
measured)

Velocity (m / s)
Momentum (kg • m / s)
Total momentum
before collision
Both gliders after
collision
Data and Analysis
Percent Difference for Total Momentum Calculations
You can compare the total momentum before and after the collisions by looking at the numbers and estimating if
they are close together or far apart. You can make a more precise calculation by using the following formula for
percent change in momentum.
% change in p =
pafter − pbefore
pbefore
 100
Calculate the change in momentum for each of your trials.
Change in Momentum
Criteria
Elastic
Collisions
Elastic
Collisions
Elastic
Collisions
Inelastic
Collisions
Inelastic
Collisions
Inelastic
Collisions
Trial 1
Trial 2
Trial 3
Trial 1
Trial 2
Trial 3
% change in
p
Answer the questions in the LRD to prepare for the Discussion.
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