Development of a software tool for use in University Physics Laboratories

Development of a software tool for use in University Physics LaboratoriesDoug Harper, Scott BonhamWestern Kentucky University

I will describe a new software tool that we have developed at Western Kentucky University for use in our University Physics Laboratories.1Development of a software tool for use in University Physics LaboratoriesDoug Harper, Scott BonhamWestern Kentucky University

We call this software Physics Lab Assistant and it was developed in LabVIEW by National Instruments which we use in a variety of ways throughout our curriculum and research.2University Physics Laboratory at WKUOriginal curriculum developed in 1998NSF Instrumentation and Laboratory Improvement Program: Transferable-Skills-Based University Physics Laboratories Doug Humphrey and Doug Harper

Experiments focus on verifying various physics principles and require students to use LabVIEW (National Instruments, www.ni.com) based software tools to acquire data.

Data is often processed in Excel and analyzed in scientific graphing software called Igor Pro (Wavemetrics, www.wavemetrics.com).

Detailed instructions for the experiment are provided to students in their laboratory manual.

The curriculum that we had been using was developed in 1998 after receiving an NSF Instrumentation and Laboratory Improvement grant entitled Transferable-Skills-Based University Physics Laboratories. In this curriculum students performed experiments that generally focused on verifying laws of physics. We used LabVIEW to acquire data from sensors. Generally, students would export this data to Excel if necessary to process the data and then use the scientific graphing program Igor Pro to further analyze the results. Students were provided rather detailed instructions in their laboratory manuals that they could easily follow on their own to complete the experiment.3University Physics Laboratory at WKUNew curriculum developed in 2012NSF Course, Curriculum and Laboratory Improvement: Multidisciplinary Instructional Transformation in Science and Math Courses Supporting Teacher Preparation and Institutional Change Scott Bonham (PI)

Instructions to students in laboratory manual are more open ended and much less detailed.

Pre-lab exercises are used to provide necessary background information to students prior to lab.

New skills are introduced in a scaffolded manner to students throughout the semester.Our latest curriculum was developed between 2010 and 2012 supported by a NSF Course, Curriculum and Laboratory Improvement grant. The most significant difference in this curriculum is that the laboratory instructions provided to students are much more open ended and less detailed than before giving the students more flexibility and opportunities to be creative in their approach to the experiment. Necessary background material was removed from the instructions and provided to the students via pre-lab questions delivered via Blackboard. We introduce new skills in a scaffolded manner to the students throughout the semester.4Learning ObjectivesStudents completing WKU University Physics I Laboratory should be able to:

Demonstrate improved conceptual understanding of foundational physics concepts on a conceptual assessment.Develop experimental procedures to carry out an investigation to test a hypothesis.Employ good measurement techniques, including calibration of sensors, reading scales, recording units and keeping good records.Collect data, produce standard formatted graphs, and interpret the data.Prepare properly formatted graphs and analyze/interpret them. Be able to identify, minimize and quantify uncertainty in measurements, estimate uncertainties in calculated results, and compare with other results.Carry out appropriate analysis of data using physical models (e.g. equations), including numerical differentiation and integration.Be able to write technical reports as assessed by an appropriate rubric.Effectively function in teams to accomplish different tasks.Students will be able to reproduce a result from a different science team.Report having a positive learning experience in the course.

We developed a set of learning objectives to guide the new curriculum development. These objectives were rather ambitious but cover the basic skills that most of us would want students to master in a University Physics Laboratory. Two of these objectives required that students be able to measure physical quantities using sophisticated data acquisition and be able to develop their own experimental procedures. The software was designed to support these objectives. 5Software Design GoalsWe wanted a software tool that would provide a user experience that would not get in the way of learning physics concepts and laboratory skills.

Flexible usable for many different experiment types.Intuitive easy for students to use.Accurate for both acquisition and analysis.Efficient students can acquire and analyze data.Scalable allows scaffolding of experimental design.

We wanted a software tool that would not become the focus of the student experience but rather something that was so easy to use that the focus could be more on the physics rather than what needed to be done within the software. We wanted the software to be flexible enough to support all of our experiments, to be able to be used for acquiring and analyzing data, and to support a scaffolded approach that allowed students to ease into using the software over the course of a few weeks. In coming up with a name for the software we decided upon Physics Lab Assistant because the role of the software was much like a lab assistant in that it is there to help the student to achieve his/her objectives.6

Here is a screenshot of the software.7

Experimental Setup Area

Students create and definewaveformsconstantscalculated valuesin a custom fashion for different experiments.The heart of the software is contained in this experimental setup area at the bottom where students can create and define waveforms, constants, and calculated values that will be used in the experiment. Of course a waveform is a collection of values evenly spaced in time.8

Data Acquisition Control Area

Data acquisition can be easily started and stopped with the press of a front panel button or a key on the keyboard.

After the student designs the experimental channels to be acquired and the calculations to be performed they simply hit this acquire button to start data collection which is displayed in real time on the central portion of the screen.9

Waveform Data Export Area

Waveform data can be exported to:

MS Word images of graphs inserted in word document.Igor Pro waveform data as Igor text files.Excel waveform data in Excel compatible file.Text waveform data in tab-delimited form.

The students can export the results as images to be included in a report or as the raw data to be used in other analysis software.10

Calculations Export Area

Calculations are single values such as a slope, average value, standard deviation, etc. calculated from a subset of a waveform.

Result from multiple runs are tabulated and can be exported to Igor Pro, Excel, or a tab-delimited text file.The software can be setup to calculate values from the waveform data and this area controls when a new calculation is made and allows the students to export a table of calculated values out of the software.11

Experimental Setup File Area

Definitions of waveforms, constants, and calculated values can be saved to an configuration file so that the experiment can be easily resumed/repeated.

These setup files allow faculty to provide assistance early in the term and the students to have to define everything later in the term.

Here are buttons to allow the student to save the experimental setup to a file so that it can be easily recalled later if necessary to repeat the experiment. We also use this feature to provide some preconfigured setup files for experiments early in the semester but soon the students are able to design their own experimental approach and set up the software accordingly.12

Tab Controls for Main Display

These tabs change the main display area to show:

Acquired waveforms in a real-time graph.A data table of all waveform values.A set of waveform graphs grouped by units.An x-y graph of one waveform versus another.A table of calculated values tabulated from repeated runs.

The main display can change using this tabbed interface from showing the acquired waveforms in a real-time graph, to a data table or set of graphs showing all of the waveform results, to a table that shows the values that are calculated from the waveform data.13Waveforms, Constants, and CalculationsTabbed interface separates common waveform typesacquired waveforms: sonic ranger, analog input, encoderderived waveformsconstantsformula waveformscalculated values

Looking closer at the experimental setup area it includes opportunities for the students to define what waveforms that they want to acquire along with other waveforms and values that they wish to calculate from the acquired data.14Waveforms, Constants, and CalculationsAcquired Waveformssonic ranger waveforms: position.analog input waveforms: force, pressure, temperature (anything that outputs a voltage signal).encoder waveforms: Pasco rotary motion sensor.Each acquired waveform channel is associated witha descriptive name.a unique variable (used for calculations).physical channel information.calibration factors (gain and offset).

The students can define a set of waveforms to acquire from sensors such as sonic rangers, or anything that outputs an analog value, to an encoder. Each acquired waveform channel is associated with a descriptive name, a unique variable that becomes used for later calculations, and the physical channel information and calibration factors.

15Waveforms, Constants, and CalculationsButtons control basic waveform operations Add waveformDelete waveformMove up or down in listCalibrate waveformCheck waveformSet timing parameters.

There is an easy to use button interface that allows students to add, delete, and calibrate waveform channels, or set the timing parameters for the data acquisition. Here the student has create a position waveform that is acquired from Sonic Ranger 1 and associated with a variable x and has units of meters.16Calibration Wizard: Sonic Ranger

When they choose to calibrate a sensor they use a wizard that guides them through the process of collecting two measurements at known values to compute a linear calibration and verifying the calibration at a third point.17Calibration: Sonic RangerStudents calibrate using a wizard that guides them through measuring the sensor output at two widely separated values and then verifying the calibration at an intermediate value.

Calibration factors (gain and offset) are stored with the channel information and in the experiment file if the student saves the experimental setup.

The calibration factors in the form of a gain (slope) and offset (intercept) are stored with the channel information and in the experiment file.18Sensor Check: Sonic RangerUseful for checking proper operation of sensor.

At any time students can easily check the operation and calibration of a sensor using the Check feature shown here which displays a screen showing repeated measurements from the sensor. Here the student is moving a cart along an air track in front of a sonic ranger.19Timing Parameters

Independently control the data collection rate for thesonic ranger, analog input, and encoder waveform channels, along with the total collection time.

Students can control the data acquisition rates of the sensors as well as the total amount of time that the data acquisition will last by editing the timing parameters.20Derived WaveformsUsed to compute the derivative, integral, or power spectrum of any previously defined waveform.

After defining the acquired waveforms the students set up additional waveforms that are derived in the form of either derivatives, integrals, or power spectra from the acquired data. Here the students have defined a velocity waveform that will be the derivative of the position and then an acceleration that will be the derivative of the velocity.21Derived WaveformsOnly previously defined waveforms are allowed choices for the argument of the operation.

The waveforms available for the calculation are provided in a drop down menu allowing the student to not be able to select an invalid argument for the operation.22ConstantsStudents define variable names to be associated with any constant values that will be required in further calculations.

Variable names must be unique and cannot collide with previously used variables for the acquired or derived waveforms.

Students can define variables names to be associated with constant values that will be used in later calculations. All of the variable names must be unique and cannot collide with previously used variable names for acquired or derived waveforms. Here the student defines values for the mass of the air track glider, the acceleration due to gravity, and the angle of inclination on an air track.23Formula WaveformsWaveforms can be computed from algebraic formulas involving any previously defined waveforms or constants.In this example:Gravitational Potential Energy depends on position, mass and inclination angle,Kinetic Energy depends on mass and velocity,Total Energy depends on GPE and KE.

With all of this information now the students can create additional waveforms that are computed from algebraic formulas that involve any previously defined waveforms or contents. In out example the students calculate the potential energy of the glider from its position on the incline and mass, it kinetic energy from its mass and velocity, and its total energy by adding the potential and kinetic energies.24AcquisitionDuring data acquisition all acquired waveforms are updated on the main graph in real time.

Here is an example of the data being acquired. All of the acquired waveform channels are shown in real time on the main display as the data is acquired. This is showing the position of the glider on the air track as it is released from the top of an inclined track and it bounces at the bottom of the track several times.25Data TableWaveforms can be inspected in tabular form.

The waveform data can be inspected in tabular form (although this is seldom used).26Waveform GraphsWaveforms are grouped by their units into separate graphs.

In the waveform graph display all of the waveforms are displayed on a multi-chart plot where they are grouped according to their units. Here we see the position data in the top graph, the velocity in the middle graph, and all of the energies (gravitational in purple, kinetic in light blue, and total energy in black) in the bottom graph. The student can easily see how that the total mechanical energy is conserved as the glider moves up and down the incline except for a small decrease due to friction but then a significant amount is lost during the inelastic collision with the bumper at the bottom of the track.27Waveform GraphsA cursor tool allows students to zoom on a region of interest.

This is just a second example where the student inclines the plane at a higher angle and acquires for the same amount of time. There is a cursor tool on the bottom of the screen that allows the student to zoom in on an area of interest as shown in the next slide.28Zooming on Area of InterestOnce an region of interest has been identified the student can calculate something specific from that region.

Students can identify a region of interest, zoom in on it using a cursor tool, and then calculate something specific from that region. As an example if the student wanted to compute the acceleration of the glider from the velocity she could set up a calculation to find it from the slope of the velocity in this selected region as shown on the next slide.29Calculated ValuesThe system can calculate single values from any waveform.Start and stop time based upon the zoom level of the waveform graph.Items that can be calculated include:average valuestandard deviation slopefrequencyamplitude

Students can calculate any single value that they require from the waveforms using functions such as average value, standard deviation, slope, frequency, or amplitude.30Building Tables from Repeated TrialsRepeating experiments to obtain multiple results that can be compared becomes very easy.

In this manner students can set up a particular experiment and then very easily perform repeated trials as shown here where there are multiple trials at an inclination of about 0.1 radians followed by additional trials at a higher inclination angle.31Experiments WKU University Physics I LaboratoryMeasurementPosition and VelocityAccelerationFree FallForcesFrictionMomentum and ImpulseConservation of EnergyRotational MotionSimple Harmonic MotionDamped Harmonic MotionIdeal Gas LawThermodynamic Cycle

This is a list of experiments that we perform in the first semester University Physics Laboratory. This software is used in every experiment except the first week when the students perform a basic measurement exercise.32Thermodynamic Cycle Experiment

Here are a couple of photos of the software in use in our laboratory. This shows Professor Bonham assisting a student this week performing the thermodynamic cycle experiment. You may be able to see on the screen a plot of pressure versus volume which shows the feature where one waveform (pressure) can be plotted versus another (volume) on an XY graph.33Thermodynamic Cycle Experiment

SummaryPhysics Lab Assistant has proved to be a flexible and powerful yet easy to master software tool for acquiring and analyzing data in our University Physics Laboratories.Students can use the software to design their own experiments by defining what they want to measure and what that wish to calculate from these measurements allowing opportunity for repeated trials under different conditions.We are working toward releasing an open-source version of this software that can be used with your own sensors or sensors purchased from National Instruments. Contact doug.harper@wku.edu for more information.Physics Lab Assistant has proved to be a flexible and powerful yet easy to master software tool for acquiring and analyzing data in our University Physics Laboratories. Students can use the software to design their own experiments by defining what they want to measure and what that wish to calculate from these measurements allowing opportunity for repeated trials under different conditions. We are working toward releasing an open-source version of this software that can be used with your own sensors or sensors purchased from National Instruments. Contact me at this email for more information.

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