PHYSICS SEMESTER ONE
AIR TRACK LAB
ACCELERATED MOTION
Lab format: this lab is a remote lab activity
Relationship to theory: This activity involves the motion of bodies under the influence of
constant acceleration.
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
ACCELERATED 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 – Calculating the Value of g ....................................................................... 5
(Optional) Exercise 2 – Initial Velocity ......................................................................... 6
(Optional) Exercise 3 – Statistical Analysis .................................................................. 6
Appendix A : Introduction to the Remote Equipment and Interface: ............................ 7
Creative Commons Attribution 3.0 United States License
1
PHYSICS SEMESTER ONE
AIR TRACK LAB
LEARNING OBJECTIVES

determine experimentally the value of the local acceleration of gravity by determining
the relationship between position and time for an object free falling in the local
gravitational field

apply elementary statistics to arrive at the value of the constant free fall acceleration

determine the relationship between time and distance under constant acceleration

apply trigonometric relations to determine the local value of the acceleration of gravity

determine the percent error of the experimental result assuming the accepted value of
the local acceleration of gravity of 9.8 m/sec2 is correct
BACKGROUND INFORMATION
Our goal is to determine the relationship between the position and time for an object
moving with a constant acceleration. You can do this by simply noting the time for the object to
reach certain positions. 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 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 onedimensional 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:
If an object's velocity changes with time, it is being accelerated. We are going to look at the
case where the acceleration is constant and causing the object to speed up. Acceleration is the
rate of change of velocity so a constant acceleration implies a constant rate of increase in
speed. This means that the equation for the velocity will be v = v0 + at, where a is the constant
acceleration and v is the velocity that increases with time. The position or the distance traveled
is more complicated than in the case of constant velocity, because as the objects speeds up, it
starts covering greater distances in equal amounts of time. The result is not a linear
relationship, but a power law relationship. If the initial velocity is zero, then the distance
traveled in the case of a constant acceleration obeys the following equation: d = v0t + 1/2 at2. In
our experiments, the initial velocity, v0, will be zero, so the equations will reduce to: v = at and
d = 1/2 at2.
Creative Commons Attribution 3.0 United States License
2
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.
Creative Commons Attribution 3.0 United States License
3
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 acceleration of the sled will be
to generate a statistically significant set of data, and calculate the mean of the sample
distribution. A total of ten "runs" will be made in which four discrete points in the linear path
will be recorded. The rows of data will be statistically analyzed. The values will be plotted to
determine the acceleration of the sled. Since the track is sloped, we will use the relationship
that a = g·sinθ (acceleration down the slope = [gravitational acceleration]sinθ) to determine
value of the local acceleration of gravity. We will repeat this process for sleds of different
masses to investigate the relationship between the acceleration of gravity and the mass of the
object being accelerated.
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.
200.0 cm
X cm
θ
Figure 1 - Illustrative diagram (not to scale)
Remember that opposite/hypotenuse = sin θ
Creative Commons Attribution 3.0 United States License
4
PHYSICS SEMESTER ONE
AIR TRACK LAB
EXERCISE 1 – CALCULATING THE VALUE OF G
In this exercise, you will calculate the value of the gravitational constant, g, which is equal to
9.80 m/s2 at sea-level. You will use sleds of different masses to do this and compare the results.
Pre-Exercise questions (answer these before you do the exercise):
A. Will the heavier sled have a faster final velocity than the lighter sled? Why or why not?
B. Will the heavier sled accelerate more quickly than the lighter sled? Why or why not?
C. Complete this sentence: A heavier sled will accelerate _________________ than a light
sled.
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 removed from 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 capture the sled with the electromagnet
on the left end of the air track (you may need to decline the track to bring the sled back
down to the electromagnet).
5. Incline the air track to between 4 and 10 cm.
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.
Creative Commons Attribution 3.0 United States License
5
PHYSICS SEMESTER ONE
AIR TRACK LAB
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.
6. Use the angle relationship to determine the value of g from the value of the slope.
Post Exercise Questions:
D. Are the values of g the same or different for the two different mass sleds?
o What evidence do you have to support your conclusion?
E. Are the values of the final velocity for each sled (measured at photogate 4) the same or
different?
o What evidence do you have to support your conclusion?
F. Did the results of this experiment agree with your expectations or not? Explain.
(OPTIONAL) EXERCISE 2 – INITIAL VELOCITY
Use the graphs you prepared in Exercise 1 to determine the initial velocity at time = 0.
G. What did you determine the initial velocity of each sled to be, based on the graphs?
H. Explain what this means, in terms of introduced error in your determination of the value
of g.
I. If the initial velocity of the sled was not zero, explain what you think could have caused
this to be the case.
(OPTIONAL) EXERCISE 3 – STATISTICAL ANALYSIS
Calculate the value of g for each set of data, so that you have 10 values of g for each sled.
Perform a t-test to determine if the average values are statistically different from each other.
J. Are the values of g statistically the same or different for the two different mass sleds?
(support your answer with statistical calculations)
Creative Commons Attribution 3.0 United States License
6
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 2 and Figure 5 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 2 - 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.
Creative Commons Attribution 3.0 United States License
7
PHYSICS SEMESTER ONE
AIR TRACK LAB
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.
The electromagnet located on the left end of the airtrack looks like this:
Figure 3 - 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 4 - Electromagnet with Launcher Attachment
Creative Commons Attribution 3.0 United States License
8
PHYSICS SEMESTER ONE
AIR TRACK LAB
Figure 5 – RWSL Airtrack Control Panel: Data Tab
Figure 5 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 6 (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 7 (below) shows the preset list for camera 2.
Figure 8 (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.
Creative Commons Attribution 3.0 United States License
9
PHYSICS SEMESTER ONE
AIR TRACK LAB
Figure 6 - Camera 1 Presets
Figure 7 - Camera 2 Presets
Creative Commons Attribution 3.0 United States License
10
PHYSICS SEMESTER ONE
AIR TRACK LAB
Photogate 1
The 10.0 cm flag
Figure 8 - Sled and Photogate
The electromagnet
“launcher”
Creative Commons Attribution 3.0 United States License
The sled
11