PHYSICS SEMESTER ONE
AIR TRACK LAB
CONSERVATION OF MOMENTUM AND ENERGY
Lab format: this lab is a remote lab activity
Relationship to theory: This activity involves the study conservation of energy and momentum
in collision
Instructions for Instructors: This protocol is written under an open source CC BY license. You
may use the procedure as is or modify as necessary for your class. Be sure to let your students
know if they should complete optional exercises in this lab procedure as lab technicians will not
know if you want your students to complete optional exercise.
Remote Resources: Primary - Airtrack, Secondary - None.
Instructions for Students: Read the complete laboratory procedure before coming to lab. Under
the experimental sections, complete all pre-lab materials before logging on to the remote lab,
complete data collection sections during your on-line period, and answer questions in analysis
sections after your on-line period. Your instructor will let you know if you are required to complete
any optional exercises in this lab.
Contents
CONSERVATION OF MOMENTUM AND ENERGY .......................................................... 1
Learning Objectives ..................................................................................................... 2
Background Information ............................................................................................... 2
Equipment ................................................................................................................... 3
Preparing to Use the Remote Web-based Science Lab (RWSL) ................................. 3
Introduction to the Remote Equipment and Control Panel ........................................... 3
Experimental Procedure: ............................................................................................. 4
Exercise 1 – Kinetic Energy and Momentum in an Inelastic Collision .......................... 5
(Optional) Exercise 2 – Statistical Analysis .................................................................. 6
Appendix A : Introduction to the Remote Equipment and Interface: ............................ 7
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PHYSICS SEMESTER ONE
AIR TRACK LAB
LEARNING OBJECTIVES

Measure the velocity of an object before and after a collision.

Determine the relationship between the momentum and kinetic energy of an object
before and after an inelastic collision.

Determine whether kinetic energy and/or momentum is conserved during an inelastic
collision
BACKGROUND INFORMATION
Our goal is to determine the relationship between the kinetic energy and momentum of
two objects before and after an inelastic collision. To remove friction you will use an airtrack,
which is a linear track that has many holes through which air blows, suspending a sliding cart or
sled. The sled moves along on a layer of air and does not actually touch the underlying track.
The air-track is a one-dimensional version of the common air-hockey table, so the sled can only
move in one dimension.
You will be using the Remote Web-based Science Lab (RWSL) facility in Denver, CO to perform
this experiment. It is a real lab that you will access through the Internet using your computer.
You will access the experiment through the RWSL Lab Scheduler in your D2L course.
Theory:
Conservation of linear momentum and energy are examined in this lab. Conservation laws are
among the most important parts of physics. By definition, the value of a conserved quantity
before a physical process begins is the same as the value of the conserved quantity after the
process has occurred. Any physical process brings something from an initial state to a final
state, and the final state can be quite different from the initial. The conservation laws give us a
way of comparing these two states. That is the root of their importance in physics.
The conservation of linear momentum of an isolated system is a core law of physics. The total
momentum of a system before a collision is always equal to the final total momentum, since
the system of colliding objects can be considered as isolated during the collision. External
influences are negligible compared to the strength of the interaction between the colliding
bodies during the collision, and the short duration of the collision.
You will examine inelastic collisions in this lab activity. Elastic collisions conserve the kinetic
energy of the system as well as momentum. A completely (or perfectly) inelastic collision, in
which the two objects stick together, is a special case that will be considered. The kinetic
energy of the system is not conserved during an inelastic collision.
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PHYSICS SEMESTER ONE
AIR TRACK LAB
EQUIPMENT

Paper

Pencil/pen

Computer (access to remote laboratory)
PREPARING TO USE THE REMOTE WEB-BASED SCIENCE LAB (RWSL)
Click
on
this
link
to
access
the
Installguide
for
the
RWSL:
http://denverlabinfo.nanslo.org
Follow all the directions on this webpage to get your computer ready for connecting to
the remote lab.
INTRODUCTION TO THE REMOTE EQUIPMENT AND CONTROL PANEL
Watch this short tutorial video to see how to use the RWSL control panel:
http://denverlabinfo.nanslo.org/video/airtrack.html
There are appendices at the end of this document that you can refer to during your lab if
you need to remind yourself how to accomplish some of the tasks using the RWSL
control panel.
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PHYSICS SEMESTER ONE
AIR TRACK LAB
EXPERIMENTAL PROCEDURE:
Read and understand these instructions BEFORE starting the actual lab procedure and collecting
data. Feel free to “play around” a little bit and explore the capabilities of the equipment before
you start the actual procedure.
Summary of Experimental Procedure:
We will set up the experiment with one sled positioned at rest in the middle of the airtrack and
one attached to an electromagnetic launcher device on the left end of the airtrack. The sled on
the launcher will have a device with a wax cylinder and the other one will have a device with a
needle on it that will cause the two sleds to stick together when they collide, as shown in the
two images below.
Photogates 1 and 2 will be used to measure the velocity of the sled that is launched and
photogates 3 and 4 will be used to measure the velocity of the two sleds after the collision.
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PHYSICS SEMESTER ONE
AIR TRACK LAB
Instantaneous Velocity Values:
The timing data display consists of the eight numerical fields labeled "Photogate 1, 2, 3, 4". The
first number is the time value in seconds that has elapsed since the sled was launched and the
leading edge of the flag mounted on the sled coincided with the prepositioned photogate. The
second value is the time in seconds that has elapsed since the leading edge of the flag initiated
the signal and the trailing edge interrupted the signal. Thus, the time between these two
values is how long it takes the flag on the sled (length = 10.0 cm) to pass through one
photogate. This way, we can measure the instantaneous velocity as the sled passes through
each photogate.
EXERCISE 1 – KINETIC ENERGY AND MOMENTUM IN AN INELASTIC COLLISION
Pre-Exercise questions (answer these before you do the exercise):
Complete the following sentences:
A. The combined sleds after the collision will have a velocity
______________________ than the single moving sled before the collision.
that
is
B. The combined sleds after the collision will have a momentum that is
______________________ than the single moving sled before the collision.
C. The combined sleds after the collision will have a kinetic energy that is
______________________ than the single moving sled before the collision.
For all steps involving moving sleds, use the robot arm, if available, or ask the Lab Technician to
assist you.
Data Collection
1. Ask the Lab Technician to ensure that the launcher attachment is installed on the
electromagnet.
2. Using the robot arm (if available), or asking the Lab Technician to assist, place each sled
onto the electronic scale and determine the mass.
3. Ensure that the air pump is turned on, and place the sled with the needle in the middle
of the air track.
4. Click the gray “Click to Capture Sled” button energize the electromagnet.
5. Place the other sled onto the airtrack and load it onto the launcher.
6. Make sure Trial Number 1 is selected on the Controls tab, and click the green “Click to
Launch Sled” button.
7. Select the Data tab and make sure the data table fills in for Trial 1. Write down these
numbers to analyze at a later time.
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PHYSICS SEMESTER ONE
AIR TRACK LAB
8. Return to the Controls tab and increment the Trial Number so you don’t over-write your
previous data.
9. Repeat steps 3 through 8 to get a total of ten runs. Rotate control of the control panel
to allow each student in your group to collect at least one set of data. You can collect
more data than this if you want to and have time.
10. Record all data in an appropriate table in your notebook or on your computer.
Analysis (can be done after your lab period if you run out of time):
1. Prepare a data table in Excel and enter all the times from your 10 runs of data.
2. Remember that photogates 1 and 2 are for the launched sled, and photogates 3 and 4
are for the combined sleds after the inelastic collision.
3. From your ten data sets, calculate the average velocity of the single sled before the
collision, and the average velocity of the combined sleds after the collision.
4. Use the masses and velocities you determined to calculate the momentum and energy
of the sleds before and after the collision.
5. Record all your data in an appropriate table.
Post Exercise Questions:
D. How did the velocity of the combined sleds compare with the velocity of the single sled?
E. Was momentum conserved in the collision?
o What evidence supports your conclusion?
F. Was kinetic energy conserved in the collision?
o What evidence supports your conclusion?
G. Did the results of this experiment agree with your expectations or not? Explain.
(OPTIONAL) EXERCISE 2 – STATISTICAL ANALYSIS
Calculate the velocity of the single and combined sleds for each of the 10 data sets.
H. Was the velocity of the combined sleds statistically the same or different than the
velocity of the single sled? (present statistical calculations to support your answer)
I. Quantify the experimental error in the average velocity for the single sled and for the
combined sleds. (present statistical calculations to support your answer)
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PHYSICS SEMESTER ONE
AIR TRACK LAB
APPENDIX A : INTRODUCTION TO THE REMOTE EQUIPMENT AND INTERFACE:
We will be using the RWSL to collect data for this experiment. Here is a quick introduction to
the control panel that you will use to control the equipment and to see what is happening in
the lab. Take a look at Figures Figure 1 and Figure 4 to see what the control panel looks like.
On the left side of the screen are equipment controls, and on the right side is a video window
with camera controls. You will use a robot arm and a screw-drive robot to move and position
the equipment as necessary. (NOTE: If the robot arm is not available, as shown below, then
use the voice conference line to ask the Lab Technicians to assist you in placing items.)
Click here to turn on
the Air Supply
If it is green, then the
pump is already on.
Robot arm controls
will appear here if they
are available.
Figure 1 - RWSL Airtrack Interface: Controls Tab
Instructions for joining voice
conference.
From the Controls Tab, you can raise and lower the left end of the airtrack, energize and deenergize the electromagnet on the left end of the airtrack, and select which trial number to
populate with data from the photogates.
If the robot arm controls are available, you will also be able to put sleds on and off the track,
onto the electronic balance, etc.
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PHYSICS SEMESTER ONE
AIR TRACK LAB
The electromagnet located on the left end of the airtrack looks like this:
Figure 2 - Electromagnet on Airtrack
It can also have a launcher attachment mounted on it that uses a rubber band to push the sled
down the track:
Figure 3 - Electromagnet with Launcher Attachment
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PHYSICS SEMESTER ONE
AIR TRACK LAB
Figure 4 – RWSL Airtrack Control Panel: Data Tab
Figure 4 shows the Data Tab. From here, you can select which trial number to view, as well as
see the mass of whatever is on the electronic balance and control the balance itself.
Figure 5 (below) shows the camera 1 preset positions. If you hover over the gray boxed area
of the preset buttons, a list will pop-up which tells you what each preset shows.
Figure 6 (below) shows the preset list for camera 2.
Figure 7 (below) shows the sled sitting on the left end of the airtrack, and has annotations to
indicate the sled, the flag, the electromagnet and photogate #1. The 4 photogates are
numbered #1 - #4 from left to right and are labeled with numbers. You can use the cameras to
inspect them more closely.
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PHYSICS SEMESTER ONE
AIR TRACK LAB
Figure 5 - Camera 1 Presets
Figure 6 - Camera 2 Presets
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PHYSICS SEMESTER ONE
AIR TRACK LAB
Photogate 1
The 10.0 cm flag
Figure 7 - Sled and Photogate
The electromagnet
“launcher”
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The sled
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