PHYSICS SEMESTER ONE
AIR TRACK LAB
UNIFORM MOTION
Lab format: this lab is a remote lab activity
Relationship to theory: This activity involves the motion of bodies under constant velocity.
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 - Launcher.
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
UNIFORM MOTION ........................................................................................................ 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 – Measuring the Velocity of the Sled .......................................................... 4
(Optional) Exercise 2 – Statistical Analysis .................................................................. 5
Appendix A : Introduction to the Remote Equipment and Interface: ............................ 7
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PHYSICS SEMESTER ONE
AIR TRACK LAB
LEARNING OBJECTIVES

determine the relationship between position and time for a body moving with constant
velocity

apply elementary statistics to experimentally observed data to arrive at the value of the
constant velocity of the body

demonstrate graphically and mathematically, from the observed experimental data, the
relationship between distance and time when velocity is constant
BACKGROUND INFORMATION
In this experiment we will investigate motion without acceleration. Motion without
acceleration is uniform (constant velocity) motion, which means it describes the motion of an
object that has constant speed and constant direction. Accelerated motion is the motion of
something with either a changing speed or a changing direction. In the next experiment, we will
deal with changing speeds.
Our goal is to determine the relationship between the position and time for an object moving
with a constant velocity. You can do this by simply noting the time for the object to reach
certain positions. First however you must put an object into constant velocity motion. One way
to do this is with a constant velocity motor. Many motor driven toys and model cars work this
way. In this experiment however, you will use a non-motorized object. Unfortunately, most
non-motorized objects don't move with a constant velocity because they slow down and stop
after a relatively short period of time. In order to keep an object from slowing down, you must
remove friction. Later you will learn that an object moving with no friction and no external
forces acting on it will move forever with a constant velocity.
To remove friction you will use an air-track which is a linear track that has many holes through
which air blows, suspending a sliding 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 which has a suspended puck free to move in two dimensions. To start the sled
moving, a small rubber band is used to give it a push when you release the sled from the
launcher by de-energizing an electromagnet on the launcher.
The position equation for an object moving with a constant velocity is:
D  vt
where D is the distance traveled, v is the constant velocity, and t is time. Since v is constant, this
equation represents a proportional relationship between distance traveled and time.
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PHYSICS SEMESTER ONE
AIR TRACK LAB
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, and you
will communicate with your lab partners and the Lab Technicians using the Mumble software
that you installed on your computer during the setup process.
EQUIPMENT

Paper

Pencil/pen

Computer (access to remote laboratory)
PREPARING TO USE THE REMOTE WEB-BASED SCIENCE LAB (RWSL)
Click
on
this
link
to
http://denverlabinfo.nanslo.org
access
the
Installguide
for
the
RWSL:
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:
The approach to the determination of the value of the constant velocity of the sled will be to
generate a statistically significant set of data, and calculate the mean, the median and the
mode of the sample distribution. A total of at least ten "runs" will be made in which four
discrete points in the linear path will be recorded. The time and distance data will be analyzed
to determine the relationship between distance and time under these conditions.
Instantaneous Velocity Values:
The timing data display consists of the eight numerical fields labeled "Photogate 1, 2, 3, 4". The
first field 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 – MEASURING THE VELOCITY OF THE SLED
Pre-Exercise questions (answer these before you do the exercise):
A. Will the heavier sled have a faster velocity than the lighter sled? Why or why not?
B. Complete this sentence: The plot of velocity vs. “time at each photogate” should have a
slope of ____________ (“greater than zero”, “zero”, or “less than zero”).
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 mounted on the
electromagnet.
2. Using the robot arm (if available), or asking the Lab Technician to assist, place a sled
onto the electronic scale and determine the mass.
3. Ensure that the air pump is turned on, and place the sled onto the air track.
4. Click the gray “Click to Capture Sled” button to energize the electromagnet and use the
robot arm/Lab Technician to reload the sled onto the magnet.
5. Ensure that the airtrack is not inclined or declined (it must be level).
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PHYSICS SEMESTER ONE
AIR TRACK LAB
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.
8. Return to the Controls tab and increment the Trial Number so you don’t over-write your
previous data.
9. Repeat for trials 2 through 10 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. Repeat this entire process for the other sled, which has a different mass.
11. 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. Calculate the average of each time measurement, so you end up with just 8 data points
for each sled.
3. Calculate the instantaneous velocity of the sleds as they pass through each photogate.
4. Plot the four velocities you calculate (y-axis) vs. the time that it was half-way through
each photogate (x-axis). For example, if it entered the photogate at 1.0 seconds, and
exited at 1.14 seconds, then it was halfway through at 1.07 seconds. (NOTE: choose
Scatter Plot, and make sure that the column of times is to the left of the column of
velocities.)
5. Add a Trendline to determine the value of the slope.
Post Exercise Questions:
C. Are the values of g the same or different for the two different mass sleds?
D. What was the velocity of each sled as it moved down the air track?
o Was this velocity truly constant?
o What evidence do you have to support your conclusion?
E. What are the sources of uncertainty that contributed to error in your results?
F. Did the results of this experiment agree with your expectations or not? Explain.
(OPTIONAL) EXERCISE 2 – STATISTICAL ANALYSIS
Calculate the average velocity at each photogate for each sled.
Perform a t-test to determine if the average value of the velocity at photogate 1 is statistically
different from the average velocity at photogate 4, for each sled.
G. Is the velocity of the lighter sled at photogate 1 statistically the same or different from
its velocity at photogate 4? (support your answer with statistical calculations)
H. Is the velocity of the heavier sled at photogate 1 statistically the same or different from
its velocity at photogate 4? (support your answer with statistical calculations)
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PHYSICS SEMESTER ONE
AIR TRACK LAB
I. Is the average velocity of the lighter sled at photogate 4 statistically the same or
different than the average velocity of the heavier sled at photogate 4? (support your
answer with statistical calculations)
J. Calculate the instantaneous velocity at Photogate 4 for each data set for the lighter sled.
You will have 10 values of velocity. Quantify the error in the average velocity at
photogate 4.
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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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