Java程序辅导
C C++ Java Python Processing编程在线培训 程序编写 软件开发 视频讲解
C C++ Java Python Processing编程在线培训 程序编写 软件开发 视频讲解
Jon M Pearce, School of Physics and Science Multimedia TeachingUnit, University of Melbourne, Parkville, Vic 3052, Australia.Phone +613 9344 8072 Fax: +613 9347 4783
Michelle K Livett, School of Physics, University of Melbourne,Parkville, Vic 3052, Australia. Phone +613 9344 8071 Fax: +6139347 4783
World Wide Web, Tertiary, Physics Education, Video analysis, Java, Australia
At AusWeb96 we reported on a development project to provide a sophisticated Javavideo analysis tool to students studying undergraduate physics (see ). Students will use the tool as part of a Web site on analysing videos of real-world events in order to help understand the physics behind them. The analysis tool, MotionWorkshop, also provides sophisticated modelling capabilities enabling students to construct spreadsheet-style models to test against the videoed events.
This paper reports on the progress of the project as well as someof the difficulties encountered along the way. The project is ongoing and preliminary trialling with students will takeplace during this year.
A continuing challenge to physics educators is students' tendencyto quarantine the physics understanding they gain during formalinstruction from their everyday lives (Arons 1990, McDermott 1991, Redish 1994). This tendency comes, inpart, from the difficulty of bringing the excitement of the physicsof the real world into a lecture theatre: trampolines, pole vaultersand space shuttles just don't fit! A solution in the past hasbeen to perform demonstrations which illustrate the concepts beingaddressed. Whilst such demonstrations are of great value and tobe encouraged, they are usually not accessible for students toplay with after the lecture when they might like to explore some"what if" questions.
These two issues - the difficulty of bringing real-world physicsto students and the one-off nature of lecture demonstrations - arethe target of a current CAUT-funded project entitled Real-WorldPhysics. The project aims to provide first year undergraduate students with a sophisticatedWeb-based analysis tool which allows them to analyse video-clips. The video-clips produced are of real events, and of lecture demonstrations. Although other examples of video analysis software exist (see, for example , , , and), they do not offer the same spreadsheet modelling facilities of this project, nor are they Web-based.
The software being developed comprises Web-based learning moduleswithin which students view closely, and analyse, short video segmentsof real-world events or key lecture demonstrations. A typicalevent might be the motion of a long-jumper or the swing of a golfclub. The video analysis will be carried out within MotionWorkshop,a Java applet. The applet is linked to a World Wide Web documentwhich provides the learning framework for students' video analysisincluding motivating questions, background information and suggestionsfor analysis.
Analysis using the applet will involve the students tracking themotion of a point or points on the moving object by clicking,frame by frame, on the video image on the screen. The resultingdata will be recorded into an on-line spreadsheet which will automaticallycalculate values of velocity and acceleration. From the spreadsheetseveral functions will be controlled:
Suitable spreadsheet quantities will also be displayed on a vectordisplay. Due to the nature of derived vector quantities, thisdisplay will be three-dimensional, and rotatable so that differentviews of the vectors can be seen.
An unusual and innovative feature of the spreadsheet will be itsthree-dimensional nature. Any quantity in the spreadsheet canbe defined as a 3-d vector. True 3-d vector operations will beavailable as regular spreadsheet formulas enabling students tomanipulate and visualise quantities in 3-d space in a manner notpreviously possible.
The spreadsheet has also been designed to simplify the generationof data using numerical modelling techniques. This will allowstudents to enter a mathematical model for a motion they are studyingand see the model's results side-by-side with the analysed videodata. This form of modelling is a powerful method of "completingthe loop" in helping understand motion. It enables studentsto set up their own models of the causes of motion, and comparethe outcomes with reality.
These analysis activities will be coupled with "virtual interviews"with people to whom the physics under examination is important.Through these we hope to provide students with insights into howthe physics ideas apply in practice. These interviews will bepresented in the Web document and, although pre-recorded and limitedin scope, will help students appreciate the fact that real peoplehave to think about real physics in real life.
By analysing real-world situations, and viewing them via thesemultiple representations, students will deepen their understandingof physics principles. Gaining insights from videoed interviewswill enhance students' perception of the relevance of physicsto their own experience.
To give an idea of exactly what the student activities involve,the following is a brief outline of a student's progress throughthe learning package.
Web Site. The student begins by accessing the project'sWeb site and selecting the assignment she wishes to study. Inthis example, it involves analysing the motion of rotating clubsas a juggler tosses them from hand to hand and then modelling themotion by using the spreadsheet. The Web document presentsthe background physics, the requirements of the assignment, presentsa short video of the motion to be analysed and solicits some feedbackfrom the student (via a Web form) concerning her initial conceptions.
MotionWorkshop. The student's next task is to launch theMotionWorkshop applet (from the Web site) and call up the videosegment for analysis. She will enter position data for one ofthe juggler's clubs by clicking on the clubin each frame of the video. These data are automatically enteredin to the spreadsheet from where she can elect to display columnsof data representing various parameters, such as velocity or acceleration.
She might choose next to plot a graph of one of her quantities.In addition, she might decide to use the spreadsheet to calculatea derived quantity, kinetic energy maybe, and display its valueson a graph.
In order to understand how the acceleration varies during themotion, she might choose to display vectors (instead of the graph) and manipulatethem on-screen. A video of the side view of the motion will enableher to construct a set of angular velocity vectors pointing inthe third dimension and explore how these vectors change duringflight.
Having formed an understanding of the nature of this motion, thestudent can begin to construct a numerical model by entering therelevant equations of motion into new columns in the spreadsheet.The data she constructs in this way can be overlaid on the originalmotion to test its validity. MotionWorkshop will provide easyways for her to change variables in her model and immediatelysee the effects. "What if" type questions will be raisedwhereby she will be motivated to consider variations on the motionand test her hypotheses by calling up a related movie clip andagain comparing this real motion to her analysis.
Reflecting on Learning. Having finished exploring the motionin the analysis tool, she will record and consolidate her learningby making entries into a prepared paper-based logbook under headings suchas "physics understanding developed", "equationsused", "modelling strategies" and "what-ifquestions".
Interview the Juggler. The final part of this assignmentwill allow her to "interview" the juggler about howhe uses a knowledge (or lack of) whilst juggling. She will choosefrom a variety of questions set up on the Web and view short video-clipsof the juggler responding. Many of these questions pick up onthe "what if" theme and might inspire further analysis. (The image opposite links to a movie of the juggler being interviewed about the difference between juggling balls and clubs. File size = 3.4MByte).
A final reflection. Back in her logbook, she will makefinal reflective comments about what she has learned, problemsencountered and her thoughts on the process.
Throughout this process, which will be done via the Web, or fromCD, at university or at home, the student will be making decisionsand seeing their immediate consequences. She will be tempted toexplore and to link the world of analytical physics to real worldscenarios. The logbook produced will be a record of what she hasdone as well as providing feedback to us about learning outcomesand student impressions.
The nature of the student activity while using this software isone of interactive engagement in a task. Students will be continuallymaking decisions about what to measure, how to calculate quantities,which features to display.
Whilst doing this, they will be viewing motions using multiplerepresentations of data. The data they view will be presentedas video, numbers, graphs and vectors. Each of these will be linkedon the screen to help reinforce their equivalence. This techniqueof multiple representations is a promising way of helping studentsdevelop the necessary analytical skills required in physics (Beichner 1990, Escalada and Zollman (in press)).
The numerical modelling aspects enable students to turn an analysissituation around into a predictive one. Rather than describe anexisting motion, they are put in the position of defining thephysics that determines the motion. This can be a demanding task,but one which is an important part of any physics learning.
Evaluations of the use of this software will endeavour to determinehow these features support students' learning and promote a deeperunderstanding of physics principles and applications.
Turning dreams into reality is often fraught with problems, andthe development of this software was no exception. The task, begunin 1996, was a substantial one for several reasons:
Allied with the complexity of the package was the need for academicoversight of each aspect of the project. The fact that academicinput cannot be full-time due to other demands like teaching,research, and administration, at times has retarded progress inthe project development. A brief description of each aspect ofthe integrated project will highlight the need for academic input.
Video: Selection of subjects to provide appropriate videomaterial requires understanding of the desired learning outcomesof the project. The package is intended to provide students withthe opportunity to develop their own understanding of motion,and to allow ample opportunity for them to confront those barriersto understanding which have been highlighted by physics educationresearch. The choices are not simply what will look good on thescreen, but what will comprise a beneficial sequence for students'learning, requiring academic judgement.
There are also overheads associated with interacting with potentialvideo subjects. This has at times included extended negotiationperiods as participants need to be reassured about their involvementin a very public project.
Software: There has been an enormous time commitment toprogram design. This is due to the complexity of the package,with the dual requirements that the applet have multiple, powerfuland flexible tools, while its design makes the use of these toolsintuitive and straightforward.
HTML: Here is where the learning package's framework ofphysics content and student assignments is found. These learningmaterials are written by physics academics and lie within a structuredesigned by an HTML programmer in collaboration with those academics. Decisions about the types of interactions students would be engagedin, the inclusion of forums, email feedback, posting questionsfor teachers' answers and for other students' perusal, need tobe made by the academics working on the project.
Graphics: The graphical design needs to serve the needsof the students, in helping them to navigate their way throughboth the HTML document and the Java applet. It requires less extensiveliaison between designers and academics at each stage.
Our experience has highlighted the demands placed on academicstaff involved in the execution of such a project. There is aclear need for significant involvement of an academic team ineach facet of the project development, limiting the possibilityof sub-contracting out various aspects of the project.
The newness of Java was a difficulty over which we had least control.Our decision to use Java, rather than an established languagesuch as C++, was a carefully considered one based on the benefitsof cross-platform operation without installation, and, of course,the requirement to give students access to the whole package viathe Web. However, although the hype of this new language wasextreme, the reality brought many significant obstacles.
The most significant obstacle was that of compatibility. Javaapplets of this type require a 32 bit operating system and willhence not run effectively under Windows 3.1. This leaves the commonoperating systems supported as Windows NT or 95, Macintosh andUnix. Current versions of applets created on a Unix workstation(using Java Development Kit 1.1) will not run exactly thesame on the Windows and Macintosh platforms. The differences rangefrom minor matters of appearance, to crucial problems of appletsnot running at all!
The execution speed of Java is also problematic. It has been measuredto be about 1.5 times slower than C, when the applet is pre-compiledusing a Just-In-Time compiler (negating the cross-platform downloadfeature). However, this performance is even slower when the appletis executed through a browser, with Netscape being about 5 timesslower than Internet Explorer, running in Windows 95! For a discussionon the execution speed of Java applets see.
Many aspects of the Abstract Windows Toolkit (a part of the Javaprogramming environment) produce objects that just don't workin some situations. These objects are components like buttons,scroll bars and dialogue boxes, and must all be tested in situwithin the applet being developed.
A serious current impediment to using Java for video analysis is that no class libraries yet exist to control QuickTime movies from within an applet. Our temporary fix for this has been to store the movies as a sequence of gif files, to be replaced by QuickTime movies when the software is available. This solution makes the movement from frame to frame very slow (at best 5 seconds per frame using Internet Explorer 3.01, more than a minute using Netscape 3.01!).
Nevertheless, our judgement was that enough support was beinggiven to Java to secure its future, and to promise that many ofthe problems mentioned above would be rectified in future releases.We have seen this happening as we have witnessed numerous improvementsas the various versions of the Java Development Kit have beenreleased. Hence our decision was to stick with Java, even if itmeant using a compiled version of our software in the short termuntil speed and compatibility problems are ironed out.
Although there have been some difficulties in the developmentof the package, the project has generated great interest and excitementamong academics across a diverse range of disciplines. The presentationwill demonstrate the software at its current (unpolished!) stageof development, display the underpinnings of its design and outlinehow students will use it as a learning environment.
Videos of the straight-line motion of an Olympic-standard sprinteraccelerating from a variety of starting positions, a juggler executingintricate patterns of parabolic projectile motion, some electromagneticdemonstrations and falling object demonstrations are now available.Also complete are interviews with the protagonists focussing onwhat they have to do to achieve the motion seen in the video. The project in its current form can be accessed from the project site .
Several aspects of the applet are functioning well. Due to theobstacles outlined earlier we have decided to carry out initialtrials of the software using a stand-alone compiled version. This will enable us to carry out formative evaluation of the userinterface while continuing with the applet development.
Evaluation will focus on the ease of use of the applet interface,the role of the package in deepening the learning of studentsand its success in countering their perception of physics havinga place only outside the real world.
In spite of the challenges of developing a complex project ina very immature programming language, the efforts are bearingfruit and the software is entering its preliminary testing phase.Much interest has been generated by this project; those wishingto follow its progress should look at the project site .
R J Beichner, The Effect of Simultaneous Motion Presentation and Graph Generation in a Kinematics Lab (1990), J. Res. Science Teach. 27, 803-815.
L T Escalada and D Zollman, An Investigation of the Effects of Using Interactive Video in a Physics Classroom on Student Learning and Attitudes, J. Res. Science Teach. in press.
L C McDermott, Millikan Lecture 1990: What we teach and what is learned - Closing the gap (1991), Am. J. Phys. 59, 301-315.
E F Redish, Implications of cognitive studies for teaching physics (1994), Am. J. Phys. 62, 796-803.
Jon M Pearce and Michelle K Livett ©, 1997. The authors assignto Southern Cross University and other educational and non-profitinstitutions a non-exclusive licence to use this document forpersonal use and in courses of instruction provided that the articleis used in full and this copyright statement is reproduced. Theauthors also grants a non-exclusive licence to Southern CrossUniversity to publish this document in full on the World WideWeb and on CD-ROM and in printed form with the conference papers,and for the document to be published on mirrors on the World WideWeb. Any other usage is prohibited without the express permissionof the authors.