Teaching with the

Remote Web-based Science Laboratory

 

 

Instructor’s guide to

AIR TRACK EXPERIMENTS

 

 

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The Remote Web-based Science Laboratory (RWSL) is a robotic and software interface designed to enable the student to access and use science lab equipment over the internet and collect authentic real-world data in real-time. This document provides information about using the RWSL air track. (For a general overview of the RWSL, see Appendix A.)

 

Introduction to the RWSL air track

 

Like all air track apparatus used in physics experimentation, the RWSL air track is designed to study motion in a low friction environment. Since very little energy is lost through friction, it can be used to study conservation of energy, the conservation of momentum for both elastic and inelastic collisions, and it can be used to determine the acceleration due to gravity.

 

The air track is mounted within a robotic frame that allows it to be levelled or set at slopes of ± 1°. The precision robotic frame utilized by RWSL is manufactured by the Velmex company. The Velmex frame also provides mounting positions for the robotic arm and other necessary equipment.

 

 

Certifying your Computer system and connecting to RWSL

 

Before users can connect to the RWSL air track, they must ensure that their computer is certified for RWSL participation. This will ensure that the particular computer configuration will perform the experiment without causing the user undue frustration or triggering server problems with the RWSL computer interface.

 

Please go to Appendix D to view instructions about how to certify your system for use with RWSL and to retrieve the software drivers required for connecting to RWSL. When this process is completed the RWSL tech will tell you when the RWSL will be ready for you to access and give you the required URL and instructions for connecting.

 

 

Communicating during RWSL experimentation

 

It is important that the students in each lab group are able to communicate among themselves during the lab session and with the RWSL tech should unexpected issues arise. Go to Appendix C for more information about options for providing this back-channel.

 

 

Experimental design

 

The RWSL technician will need the following information from you:

1. the locations for photogate placement. Your experimental design can include up to 4 photogates.¹

2. the cameras and camera presets your students should see.

3. the starting configuration for the air track and cameras.

 

Assigning group work:

You may wish to organize your students to conduct this experiment in a group. Note that although students may be conducting this experiment in a group, RWSL allows only one student at a time to control the equipment. Students working in a group should decide among themselves who will control the equipment at any given time.  They will use the Back Channel described in Appendix C for this purpose.

 

Apparatus

 

Figure 1: RWSL Air Track Apparatus

 

 

The above picture shows the Velmex frame (the black structure) with the air track, photogates, robotic arm, and scale set up within it. (The computers that animate everything are outside the shot.)

 

 

The Velmex frame

The Velmex frame (see Fig. 2, below) is a precisely constructed metal frame. A number of bi-slides and rotary tables have been mounted on the frame in various positions to accommodate a wide variety of experimental designs. The bi-slides and rotary tables are powered by stepper motors that give the user the ability to position the bi-slides and rotary tables very precisely.

 

Figure 2: The Velmex frame

 

The Velmex frame is arobotic apparatusthat can place objects in precise locations time after time. A number of bi-slides and rotary tables (powered by stepper motors) are mounted on the rigid steel frame. Its exact configuration can be changed according to lab requirements.

 

In Fig. 1, you can see how the Velmex frame is configured for an air track lab activity. There are no rotary tables used in this configuration, but you can see the steel frame, several bi-slides, and much of the air track lab set up within the frame. The horizontal bi-slide mounted on the 2 vertical bi-slides at the right hand end of the Velmex frame are used to vary the tilt of the air track up to ±1° from level and back to level again. Because of the precision motion of the Velmex frame students can accurately place the air track at a given slope or return it precisely to a level position after slope adjustment.

 

The Air Track and related Apparatus

 

Figure 3: the air track apparatus

 

Figure 4: The Air Track Cart (Glider)

 

Like all air tracks, the RWSL air track is designed so that when air is pumped through a hollow track with fine holes all along the track, a specially fitted air track cart or “glider”* can glide relatively friction-free. This makes it an ideal apparatus for studying constant motion, accelerated motion, elastic and inelastic collisions, conservation of momentum, and conservation of energy. The cart has an inverted ‘V’ base which is designed to fit neatly on to the top of the track. The cart is fitted with an opaque rectangular 10 cm long “timing flag” on the top so that it interrupts the photogates in a precisely known way. This enables the motion of the cart to be timed and its velocity calculated.

 

*Nomenclature Note – Technically the object that glides along the air track is commonly known as a ‘glider’. For several reasons, including the fact that ‘cart’ contains fewer letters than ‘glider’ and more easily fits into the limited ‘real-estate’ of the virtual instrument (VI) interface, the ‘glider’ is called a ‘cart’ in the RWSL air track VI. Hence, we will adopt the term ‘cart’ for the remainder of this document.

 

Photogates

A photogate is an inverted U-shaped device with infrared light source emitted on one side of the “U” and a detector on the other side. When the beam is broken, the photogate communicates the information to the connected computer. The photogates can be seen in this image as black inverted square “U” shapes mounted over the air track in the above image and in the image below, they can be seen mounted on the blue overhead bar. Photogates are placed along the track at known locations. A metre scale (ruler) is placed along the air track. Depending on the specific learning outcomes for the lab exercise, students can either use the cameras to read the positions of each photogate along the track or they can be provided with this information by the instructor.

 

The Robotic Arm

 

Figure 5: the robotic arm

 

In each of the previous 4 images you can see the robotic arm mounted between the air track and the scale. This arm can be programmed to perform many tasks, but in the air track lab it is used to move the carts from storage to the air track and back and from the air track to the scale and back. By selecting various camera angles, students can watch the arm in operation.

 

The Scale

The scale seen in the above images is a digital scale that can measure up to 6 kg with an accuracy of ±0.0001 kg. It provides a panel readout that students can read by using a particular camera setting, or the output can be exported to the LabView VI and displayed on the student’s screen directly.

 

 

 

Experimental Setup

 

Start-up Screen

 

Figure 6: RWSL air track start-up screen

 

When you first enter the RWSL air track Lab you will see an image similar to fig. 6, above. This image displays the RWSL air track Virtual Instrument (VI). Depending on your monitor settings you may or may not see the bottom ‘white’ portion of the screen (below the grey VI), but scrolling down on your computer display should reveal it. We’ll deal with this bottom white portion of the screen first. Note the ‘Reload Page’ button. Should you be inadvertently disconnected from RWSL or if some other technical ‘hiccup’ occurs, the VI (except for the video feed) may disappear. To restart the VI you can click on the ‘Reload Page’ button and usually restore the VI.

Whenever you initiate the VI, it will re-start the video feed with Standard video quality. You’ll notice that the Standard image quality is not as good as it might be. Clicking on the drop-down menu beside the word ‘Standard’ will reveal the following menu:

 

 

If you have sufficient internet bandwidth, you can select ‘Excellent’ to get the best possible image quality from the cameras. If you have a moderate amount of bandwidth or if the system disconnects you when you select ‘Excellent,’ you could try ‘Good.’ Leave it on ‘Standard’ if you have a smaller amount of bandwidth, or ‘Low’ if your bandwidth is seriously limited. For the rest of this tutorial we’ll assume you are able to use ‘Excellent’ video quality.

 

 

Camera controls

 

Figure 7: Air Track VI- Camera Controls

Note: This section describes the configuration of camera controls for the RWSL air track only. For a detailed overview of the RWSL camera controls, see Appendix B.

 

The camera controls for the air track lab are similar to those for other RWSL mediated lab exercises. The camera enables the student to see what she or he is working with, and can also be used to perform tasks that require observation, such as reading a scale, measuring object sizes, or the distances between photogates.

 

Camera selection

When the air track is set up within the RWSL, 2 cameras are available to students for observing the experiment. Both are pan-tilt-zoom cameras that allow students to observe the apparatus and functioning of the experiment from 2 different vantage points. Camera 1 can also be used to read the scale when the mass of the cart is required. You can request changes in the views and the number of cameras depending on what is required for your particular lab.

 

Camera pre-sets

There are multiple presets defined for each camera and you can request that more be defined.

 

“Inukshuk” control and On-Off switch

The “Inukshuk” control and on-off switch will work as described in Appendix B, for each camera.

 

 

Experiment controls

 

The RWSL air track Virtual Instrument (VI) interface is configured with two primary control screens, each displayed on a separate tab. The “Setup Experiment” tab is the one in which students perform tasks such as weighing the air track cart; moving the cart between the air track, storage, and the electronic scale; tilting the air track; and other tasks not specifically involved in gathering data. The “Run Experiment” tab is the one in which students run the lab experiments. Each screen provides a camera view.

 

The Setup Experiment Tab

 

Figure 8: Air Track VI Setup Experiment tab

 

In the Setup Experiment Tab, the cart can be loaded on the scale so its mass can be found and it can be placed onto the air track for the experimental run. For this purpose the Cart Control sub-VI is used:

Figure 9: Air Track cart control

 

Clicking on the ‘Move Cart to Scale’ button will cause the robotic arm to pick the cart from the air track and move it to the scale. The VI will be similar to the image below:

 

Figure 10: Air track controls - move cart to scale

 

The robotic arm will move the cart from the air track to the scale. While this is going on, the cart and camera VI controls will grey out, the robot activity indicator will turn green and display ‘Active’, and the arm will be observed picking the cart off the track and placing it on the scale. The indicator will change to “Cart is on the Scale”.

Once the cart is on the scale the scale analog and digital readouts will display the mass of the cart; e.g.:

 

Figure 11: Air track VI - mass of cart

 

The student may also view the scale by viewing the scale readout through the camera:

 

Figure 12: Camera view of scale

 

Once the cart mass has been recorded the student can press the ‘Move Cart to Track’ button. Again the robotic arm will move the cart from the scale to the air track. While this is going on, the cart and camera VI controls will grey out, the robot activity indicator will turn green and display ‘Active’, and the arm can be observed picking the cart off the scale and placing it on the air track. The indicator will read “Cart is on the Track”.

 

Finally the angle of the air track can be adjusted. Just under the scale readout you will see:

 

Figure 13: Air Track angle control

 

With this component of the VI, the angle of the air track can be adjusted using slider (left), level (centre), or nudge (right) controls.

 

Students can calculate the angle of adjustment by using the length of the air track carriage (approximately 171.9 cm) and the value indicated by the slider (since the slider indicates how many cm the end of the air track carriage is above or below level). A more precise digital read-out of this number in the elevation box enables students to calculate the angle themselves. The angle of elevation can be calculated with the Angle Control sub-VI: the value will be displayed under ‘Angle.’ If you want to nudge the air track up or down, use the buttons to the left of the ‘Nudge’ sub-VI pointing up and down. Note that the track can be ‘nudged’ by a value of 0.1, 0.5, or 1.0 cm.

 

Finally, the ‘Level’ button will return the track back to level. The ‘Level’ setting must be adjusted by a RWSL technician before a lab session commences. If you would prefer that the angle indicator not be displayed, be sure to indicate this to the RWSL techs before your students use the RWSL air track.

 

 

The Run Experiment Tab

 

Figure 14: Air Track Run Experiment tab

 

Clicking on the “Run Experiment” tab reveals the above sub-VI (although initially all the numbers will be zeroed). Notice that the Cart Controls are still visible at the bottom of the VI. Once the cart’s mass is known and the cart is on the air track, you can press “Load Cart”; when it’s ready, the indicator will change to “Ready to Launch”. At this point you can click on the “Air Track” button in the lower left corner. If the indicator light is red the air track compressor is off and the experiment will not work, so make sure it is green before you begin.

 

Figure 15: Air Track: ready to launch

 

Now press the “Launch Cart” button. You’ll notice a delay of several seconds while the VI initiates the photogates and the logging software, and then you will see the cart travel along the air track. The numbers will fill into the table:

 

Figure 16: Air Track data

 

The first, third, fifth, and seventh numbers in the ‘T(s)’ column are the times after launch when the air track ‘flag’ first enters the 1^st, 2^nd, 3^rd, and 4^thphotogates respectively. The second, forth, sixth, and eighth numbers under ‘T(s)’ are the times when the air track ‘flag’ leaves the 1^st, 2^nd, 3^rd, and 4^thphotogates respectively. The numbers in the ‘ΔT(s)’ column are the changes in time between each of the ‘T(s)’ times. So the first ΔT (0.219884s) is the change in time between launch (T = 0s) and when the cart flag entered the first photogate (at T = 0.219884s), the second ΔT (0.217400s) is the difference between T = 0.437284s and T = 0.219884s, the third ΔT (0.441200s) is the difference between T = 0.878484s and T = 0.437284s, etc. All times are in seconds.

 

The green buttons immediately to the right of the ‘ΔT(s)’ column indicate when the photogates are blocked or open.

 

The ‘Delay’ value visible at the bottom of the control area shows the number of ms that the photogates will stay active. It is normally set to 5000ms (or 5s) but can be varied if necessary. If the cart were to bounce back through the photogates before they were shut off then the data would be replaced by the new data coming from the photogates and the original data would be lost.

 

Up to 10 sets of data can be recorded. After each run the ‘Trial’ number must be increased by 1 – otherwise the previous trial data will be overwritten. To clear the previous run’s data click on ‘Clear Current.’ To delete the data, click ‘Delete Current’. To clear all data click on ‘Delete All’.

 

Exporting experimental data

 

To export the displayed data to your system, click on ‘Copy Data’. The currently displayed data will be copied to your computer’s clipboard. You can then paste it into your document.

 

The data set is configured best for pasting into a spreadsheet (like Excel), but can be copied into any document (including a word processor program) capable of receiving numeric data. The figure below illustrates how data appears when pasted into a spreadsheet:

 

Figure 17: data pasted into spreadsheet

 

If the data is not pasted into a spreadsheet then you will need to do some re-formatting to make it usable. The figure below illustrates how the same data set appears when pasted into Word:

 

Delta Time - Plot 0 Time - Plot 0 Delta Time - Plot 1 Time - Plot 1 Delta Time - Plot 2 Time - Plot 2 Delta Time - Plot 3 Time - Plot 3 Delta Time - Plot 4 Time - Plot 4 Delta Time - Plot 5 Time - Plot 5 Delta Time - Plot 6 Time - Plot 6 Delta Time - Plot 7 Time - Plot 7 0.332183 0.332183 0.553788 0.221606 1.003580 0.449794 1.227300 0.223719 1.674420 0.447116 1.899010 0.224593 2.360480 0.461473 2.587180 0.226699

Figure 18: raw data pasted into a word processor document

 

As you can see some reformatting would be required before this data could be represented in a document such as a lab report. The data could easily be re-arranged to look something like this in a spreadsheet or a word processor document:

 

	T	(delta) T
Launch	0.000000	-
PG 1 Start	0.332183	0.332183
PG 1 End	0.553788	0.221606
PG 2 Start	1.003580	0.449794
PG 2 End	1.227300	0.223719
PG 3 Start	1.674420	0.447116
PG 3 End	1.899010	0.224593
PG 4 Start	2.360480	0.461473
PG 4 End	2.587180	0.226699
PG = Photogate

Figure 19: formatted data in word processor document

 

 

Future development of the air track apparatus

 

The RWSL air track Virtual Instrument (VI) interface is still under development. Three capabilities are planned for incorporation into the air track in the near future. These are:

1. The ability to include more than one air track cart and to change air track carts during the experiment. This will allow experiments to be run with carts of different masses. Having more carts available would also add some redundancy options for students: if, for example, a cart is dropped during a lab session, the student can load another.

2. The capability to change the launch energy.

3. The capability for the student to change the position of the photogate(s)

4. The ability to run both 2 body elastic and 2 body inelastic collision experiments.

 

The developers of the RWSL air track are interested in other capabilities that instructors would like to add to this lab. It will take funding to make changes to the RWSL air track lab, but you are encouraged to send your ideas to the RWSL techs for consideration.

 

Multiple experiments

You can design several air track experiments to be run during an experimental session. Students may be directed to perform these experiments in sequence or according to their own preference/design. Each experiment may have its own particular requirements and interface abilities.

 

 

Summary

 

The RWSL air track apparatus enables the design and remote delivery of a variety of traditional Physics lab activities. Additional features planned for incorporation into the RWSL will enable a full spectrum of air track experimentation. Although the activities suggested here are designed for a first-semester Physics lab course, the equipment can be used to develop learning outcomes at a variety of academic levels from secondary school to more advanced undergraduate work.

 

The following air track settings can be specified in your experimental design:

• Position of photogates 2, 3 and 4

• Initial position of photogate 1

• Whether photogate 1 will be fixed in place or re-positioned by your students

• Initial tilt (if any) of the air track

• The pre-set positions of cameras 1 & 2

• The ‘Delay’ value (in ms) that the photogates will stay active. It is normally set to 5000ms (or 5s) but can be varied if necessary.

 

The following variables can be altered during experimentation by your students:

• Position of photogate 1

• Activation of the photogates

• Focussing of all 3 cameras

• The tilt of the air track

• The position of the gliders (i.e. between the air track, storage, and the electronic scale)

• The activity of the gliders on the air track (i.e. hold, release, or launch)

• The velocity of the glider launch

 

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Appendix A: RWSL Overview

 

The RWSL is a system consisting of a computer interface connected to lab apparatus.

 

The RWSL computer interface provides three main functions:

• Observation (e.g. camera)

• Data acquisition (e.g. recording, display, numeric data)

• Physical manipulation (e.g. air track launcher, robotic arm)

 

The RWSL includes a software program designed to portray these tools in a graphical user interface.

 

The RWSL lab can accommodate a wide (and growing variety) of science equipment, including a spectrometer, air track, microscope, and other apparatus encountered in a traditional science lab.

 

Fig. 1: the RWSL system

 

The RWSL system enables students to make a direct connection (over the internet) to the lab apparatus. Through this connection, students can remotely manipulate lab equipment, observe what happens, and acquire data from the experiment. The graphical user interface enables students to see and work with a set of “virtual instruments” on their computer screen, and interact with the lab equipment in a fairly intuitive way.

 

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Appendix B: RWSL Camera Controls

 

With a couple of exceptions, the camera controls for all RWSL mediated labs are always standardized on the right side of the LabView Virtual Instrument (VI) screen. In Fig. x (below) you can see the camera image as it appears for the spectrometer set-up (the image will be different when using other lab apparatus).

 

Fig. B1: RWSL Camera Controls

 

As you experiment with the various camera controls, the image above the Camera Controls will change in some way depending on which camera control you are using.

 

Camera Selection:

RWSL supports up to 4 different cameras. These are selected by clicking on the button that corresponds to each camera. You can select one of up to 4 cameras by clicking on the circular button at the lower right of the camera control area that corresponds to the camera you want. Not all RWSL lab exercises have this many cameras and those buttons not mapped to a camera will simply not respond.

 

Camera Presets:

Each camera can have up to 6 preset positions as indicated by the rectangular buttons in the Camera Controls. After selecting the camera you want to use, you can select the pre-set positions for that camera. If there are less than 6 presets, the rectangular button corresponding to an undefined preset position will simply not respond.

 

“Inukshuk” Controls (Pan, Tilt, and Zoom):

The “Inukshuk” control on the left side of the Camera Control area allows you to pan (move left and right), tilt (move up and down), and zoom (as with a hand-held digital camera) the selected camera. The selected camera must have these functions built in for these controls to work. Please refer to the camera instructions specific to the lab you are working with for these details. The ‘Inukshuk’ controls are intuitive so play with them and you will see what each of the oval buttons does.

 

 

 

Camera On/off Button:

The circular green button in the middle of the 4 directional control buttons is a toggle that will turn the selected camera off and on.

 

When you are done exploring the camera controls, you can restore the initial camera view for the lab apparatus by selecting camera 1 (the left most camera button) and pressing preset 1.

 

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Appendix C: The Communications Back-channel

 

Students assigned to a lab group must be able to communicate among themselves during the lab session and with the RWSL tech should unexpected issues arise. As the instructor, you may also wish to ‘look in’ on your students while they are performing an experiment using RWSL. There are a number of possible communications services to choose from, but the service you adopt must:

1. allow multiple participants

2. be agreed upon by all participants ahead of time

3. use minimal bandwidth so as not to degrade the connection to RWSL

 

Although video chatting might be desirable when talking to each other before and after the lab session, it’s important to remember that a streaming video connection requires a great deal of bandwidth. When connectivity is limited, this extra video connection could significantly degrade the connection to RWSL. For this reason you will probably request that your students notuse video to communicate with each other during the actual RWSL connection. Audio is important as it is the most efficient way to convey information among lab group participants. An audio connection requires significantly less bandwidth than video, and while it may degrade the RWSL connection when bandwidth is marginal, this is not so likely. Typing into a chat window uses the least bandwidth of all. Consequently your communications set-up should include a text chat feature in case the audio fails or one member of the group doesn’t have the necessary equipment to support audio communication.

 

The RWSL development team has used Google+ for back-channel communications, but other services, such as Skype, MSN, and others, are also good choices. In the case of a very small lab group (1 or 2 students) who are physically located not too far from each other or the lab tech, the telephone may also be an option.

 

When choosing and implementing a communications back-channel arrangement for your students, the following process is recommended:

1. Taking into account the bandwidth implications, comfort level and communications preferences of your students, select one or two possible back-channel communications service options.

2. Consult with the RWSL techs to determine/confirm which communication arrangement will best serve your students as they work with the RWSL.

3. Inform your students well before any RWSL lab begins so they can acquire the necessary accounts and practice using the communications set-up for this class.

4. Advise your students to use the recommended communications set up to contact each other and the RWSL tech on duty about 10 or 15 minutes before the lab session is due to begin. This will ensure that everyone is connected and can hear everyone else. The RWSL tech can give the word for the students to begin and should there be issues, everyone will be aware rather than left wondering what happened.

5. You may want to mention to your students that once the lab session is underway, the lab tech will still be available if something goes wrong. However, the tech will have other duties during this time and will only be monitoring in case of problems.

6. Since you will know how your students are communicating during the lab session, you will have the ability to ‘drop in’ to see how they are doing and respond to questions.

 

Once the lab session is over, the RWSL tech will drop out of the back-channel. The students can carry on discussing the experiment with each other if they wish.

 

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Appendix D: Certifying Your System for Connection to RWSL

 

Our ideal is that any student/instructor with a standard Internet service should be able to connect to and use RWSL. However, experience has shown that not all computer systems and Internet services work well with RWSL and in fact in some situations the remote system can cause the RWSL server to crash. We hope to rectify this situation, but for now every system that intends to connect to RWSL must be certified by the RWSL techs or it will not be allowed to connect. This will ensure the best experience for all involved.

 

Currently RWSL works only on the Microsoft Windows operating system (XP or later) and the Internet Explorer browser (version 8 or later). While we have plans for expanding these options in the future, at this time you must first make sure that your system meets these minimum conditions before proceeding. If not, you must acquire access to a system that does meet these conditions

 

To have your system certified, go to this website: http://rwsl.nic.bc.ca/installguide/. Here you can check your connection speed and download the necessary drivers. This site also has instructions for contacting the RWSL techs should you run into any issues.

 

If your system cannot be certified you may be asked to go to your local educational institution where a student system has been certified for use with RWSL.

 

Once you have your system certified or have found a system to use that is certifiable, the RWSL Tech will send you the URL you need to access RWSL.