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PHYSICS IN CONTEXT

Enriching Physics Teaching
Through Multimedia

Jon M Pearce
The University of Melbourne
School of Physics

Wednesday 3rd November, 1993

Part 1: Introduction

Caveat: I know what you'll be thinking: "yeah, it's all right for him to do it, but how do I do it in my classroom? He doesn't even use my brand of computer!". My answer is simple: some of you have the facilities now, but for many, my aim is to put forward ideas and open up possibilities for the future. It might not be possible for you next year, but it's not far off. The brand of computer is not important; the ideas are. You need to know what's possible if you are to determine the future!

Greatest thing since sliced bread

It's great! There we were, a few short years ago, cleverly crafting blocks of characters on our computer screens to make crude animations come to life. A few hours of BASIC programming later and another "educational" package was let loose on unsuspecting students. Then bit-mapped graphics came along, and soon screens were ablaze with pictures, animations, text of all shapes, sizes and colour. No more crude stick figures - this was real life. Another medium was infiltrating education.

Just as we were getting used to mixing freely text and graphics colourfully on our screens, along comes multimedia. Now even a buffoon can be taught the finer points of General Relativity as he, or she, is taken on a guided tour by Einstein himself; all the contortions of three and four dimensional thinking clearly displayed for any mind. At last, education has reached a watershed whereby the transferral of knowledge is only limited by how many bytes, megahertz and colours you can afford to buy.

So where's the problem? Why do so many sneer at multimedia as if it were the latest trendy fashion doomed to die before the next?

Alan Kay, often hailed as the father of microcomputing, makes the comment:

Most people think that by taking something and making images out of it, you can bypass what people aren't getting from books. But that's, in fact, not true. Images beg to be recognised, and words beg to be understood.

(Byte, Vol 15, No. 9, September 1990)

Defining multimedia

What is multimedia? Good question. Many will answer by saying that it is the application of a variety of electronic media to a task: computers, video, sound, CD-ROMS, laser discs, and the like. In practice, it appears that the application of multimedia to education involves presenting a great variety of different things via the computer. If the computer can present text, animations, still pictures, moving pictures, sound as well as traditional software applications, then it is regarded as multimedia.

There is no point being picky about this. The purpose of this discussion is to focus on what these aspects of computing offer to us as physics teachers, and how they will affect what and how we learn. Part of this presentation will simply illustrate good computer software that utilises well the current technology. Big M word or no Big M word, it's fun, it's motivational and it can be educational too!

All is not what it seems . . .

First, a little philosophy

Before looking at what multimedia holds in store, let's first be clear about what I am not advocating:

I am not suggesting that we replace practical laboratory work with computer exercises,

I am not suggesting that we use computing as a surrogate teacher in a tutorial-style mode,

I am not suggesting that what follows is easy and can be done without effort!

What I plan to do is to introduce you to some ideas that are easily possible on today's computers. You might have a different brand or model in your school. Never mind. They are coming closer and closer to all offering similar facilities and even running the same software.

What I am suggesting is that computer software provides us with a vehicle with which we can present interactive learning opportunities to our students. It enables us to view physics from different perspectives and might eventually even change what we teach as well as how we teach. For today, we'll steer clear of the very fancy and look at the achievable. We will focus on the use of video for demonstrations and lab work.

(Worthwhile reading, from someone who has been in the physics education business for longer than most of us, on the use of multimedia in physics can be found in Fuller's recent article in the American Journal of Physics[1]).

Part 2: Teaching with multimedia

Oh no! Where's the chalk?

In the more formal setting of a university, with large classes in well equipped lecture theatres, there is an opportunity to present one's actual teaching using multimedia facilities. Presentation software packages, such as PowerPoint[2] or Persuasion[3] offer an easy way to prepare a slick and colourful presentation. However, most schools do not have the facilities to use such software as the routine manner of presentation. Nor do I believe is it a necessarily desirable way to teach children--young or old--as it removes much of the constructive development and interaction that even chalk-boards and overhead projectors provide.

I mention such software here, in a sense, as a warning. It comes from the corporate board room and, along with spreadsheets and databases, is bound to be pushed into the classroom by zealous salespeople. It has its place, however. For presentations, such as this one, or at a conference, it is an invaluable tool.

Use of QuickTime Movies

What is QuickTime?

QuickTime is a method developed by Apple Computer to display video clips on a Macintosh computer screen. In essence, it allows the playback of video on any colour capable Macintosh (albeit slowly on some!) without the addition of any special hardware or software (other than the system software provided will all Macintosh computers). This playback can even take place over a network.

The potential of QuickTime--which we won't go into in detail here--is enormous. It has brought us simple ways to get video onto computers, sophisticated editing tools, multiple sound and text tracks, and a variety of video compression techniques to reduce the data to a reasonable size. It is now also available to run on Windows computers equipped with appropriate video and audio hardware.

Using set-piece videos and animations in teaching

Video has been with us for over twenty years as a teaching tool. A more recent modification has been interactive video, in which a videodisc player is controlled by a computer. This offers a great range of resources for physics teaching--an individual student can stop motion, go back and forth, make measurements, bring up vectors on screen, and so on. The restriction is having access to sufficient videodisc players. If you have a player, then you should look at some of the titles such as The Physics of Sport[4].

The application of video I wish to illustrate in this presentation, however, is the use of QuickTime movies generated from software such as Interactive Physics[5]. This software package is an extremely powerful simulation program which enables you to simulate the behaviour of objects in a Newtonian world (balls, blocks, irregular shapes, springs, joints, ropes, actuators); to give them various attributes (mass, elasticity, friction, charge); let them move in a definable world (setting values for gravity, magnetic fields, air resistance, force fields); watch their motion and monitor various quantities (energy, time, various vector quantities, rotation).

The complexity of the possible simulations means that the animated screen outputs often run quite slowly in real time. However, the data generated can be saved to disc (enabling them to be run more quickly next time through) and the output can also be made into a QuickTime movie to produce smooth and fast animation. Although using such `set-piece' animations reduces the opportunities for students to explore freely, they open up opportunities for a teacher to prepare sequences to use when discussing a particular concept. Faster computers in the future will obviate the need for this, but for now, there is much we can do with such animated sequences.

Producing a QuickTime movie from Interactive Physics

Having set up and run an Interactive Physics simulation, it can be saved along with its data. There is also an option that enables you to save the data to a QuickTime movie (either at the same time or later). A simple simulation might take only a few seconds to produce, but a complex one might take hours, so these data are precious! Any changes to the objects, their attributes or the other parameters of the simulation `world' will erase the data in the computer's memory ready for a new run. However, you can change `appearance' parameters that don't affect the simulation's calculations without losing data. This means you can use the same data set to produce, for example, movies with traces of the paths of various objects, their centre of mass, tracking, etc.

Once the movie is produced, it is a valuable resource in either the student's or the teacher's hands. The movie can be controlled using the regular QuickTime slider controls, allowing fine control of sequences of frames running forwards, backwards or paused. Often the feel of a motion can be acquired by rapidly moving back and forth through it using this slide control. This is a valuable feature for students to experience.

Interactive Physics tries to model:

Will the arch support the person? Is she safe under the cracked lintel?

These movies can be played using Apple's MoviePlayer application (provided free with the Apple system) or put into a HyperCard environment, offering greater flexibility. This talk shows a simple HyperCard stack set up to enable two movies to be played side-by-side for comparison. This will be useful later when we compare a real video clip with a simulated one.

Part 3: Simulation and modelling

Meanings

Let us first distinguish between the two words simulation and modelling in the context of physics education.

Simulation (in my mind, at least) refers to a carefully constructed piece of software representing a physical system. It enables a student to choose the values of parameters, output quantities for observation, choose the form of outputs (graphs, numbers, animation, etc.) and control the operation of the program as it runs. The information the computer presents should, generally, be faithful to the system being simulated. There might be exceptions to this last point in situations where you might want to see how the world would work should various quantities be different. For example, removing friction for a collision, changing the force of gravity, and so on. Usually the creator of the simulation holds the responsibility to ensure that the mathematical basis of the simulation is valid and accurate.

Modelling refers to a process of constructing a representation of a system to help better understand, or predict, the system. There are lots of computer-based modelling systems: spreadsheets, Stella[6], Resolve[7], to name three. In modelling you will be more involved with how the system works (making it an extremely powerful technique in education) and in putting together the components that make it work.

Once constructed, the model can be explored. You have no guarantee that the model is faithful to the actual system being modelled--hence verification is an important part of the modelling process. The model is likely to be a pliable construction which can be refined and modified until it agrees with measured data. This cyclic process of construction, testing and refinement is what makes modelling a powerful educational process.

The use of Interactive Physics lies somewhere between modelling and simulation. The Newtonian `world' is well defined for you by the program, as are the numerical techniques used. However, there are so many fundamental variables that can be altered, and choices of calculation methods made, that the same task could be approached by two different people in two very different ways. More importantly, it is easy to construct a model that is (unintentionally) not true to the real world! This is a positive attribute for the classroom: it means that the output of a model must be checked by some other means--students cannot rely on their model as being `true', they must test it against another source of data or even against their intuition Their own conceptions, or misconceptions, in physics may or may not agree with the computer! Computer modelling will `prove' nothing; it must not be a substitute for real experiments.

Simulations

A couple of examples of what I regard as simulations:

Electric Field Hockey[8]

This program, by Ruth Chabay, won the educational software contest run by Computers in Physics[9] for 1992. It enables the student to `play' with the concept of electric fields and try to `get a feel' for how fields affect charges. This is done in the context of manoeuvring a charged hockey ball into a goal, aided by the placement of other charges. It is interesting to note that the program is written in the language cT[10]. This language was designed for the easy production of educational software and produces programs that can be compiled to run on a variety of computer platforms (Macintosh, PC, Unix, VAX)[11].

Emfield[12]

From the same stable as the previous program, this is another approach to getting a feel for electric (and magnetic) fields. This one makes more traditional use of field lines and field vectors making it a useful way to introduce these concepts.

Gravitation Ltd 4.0[13]

I incluse this example of an astronomy simulation mainly because it is fun and it is free! There is much software to be found like this on the international network (Internet). Access to the Internet is now routine from every tertiary academic's desk, but not so great from outside such institutions. However, it is becoming more widely accessible--maybe your school soon?!?

A planet orbits a sun . . . a moon orbits a moon . . . (Gravitation Ltd)

Simulating problems

Many tertiary texts (and therefore, soon, secondary texts) are offering supplementary computer-based materials to support concept development and problem solving. Some (Giancoli[14], Fishbane[15]) have simulated a selection of their examples and end-of-chapter problems using Interactive Physics in order to give students an alternative way of approaching the problems and also as a means for playing around with the answer once solved.

Sample problems from these texts are shown below:

A text example from Giancoli

A problem from Giancoli

An example from Fishbane

Generating worksheets with Interactive Physics

Interactive Physics need not only be used to show the outcome of a model, but it can be effectively used to generate situations for analysis. The screen output can be printed and deductions made from the display of vector or scalar quantities. An object can be made invisible and its motion determined by the information provided. Consider the following screen from the program showing an elastic collision of a ball moving at 1.5 ms-1 colliding with an unknown ball (the ruler scale is in meters, the images are shown every 0.32 sec, the visible ball has mass 1.0 kg):

Right:

what information can you deduce about the invisible ball?

Completing the loop

The value of modelling is not only constructing the computer model, but playing with the model to make it agree with reality. "Reality" might come in the form of calculations, intuition, observations, experiment. In the next section we look at the use of video as a tool for this purpose.

Part 4: Image analysis and video

The video is a valuable tool for gathering data from the real world for analysis. Let's consider its use first as a check on an Interactive Physics model, then as a source of data for analysis.

Video meets model

A ping-pong ball rolls off a ramp and bounces several times. That's a tantalisingly easy model to set up in Interactive Physics.

First try at a bouncing ping-pong ball

As a check on the performance of the model, we make a video of the ball's motion and perform a comparison with the diagram to the right. This could be done by playing the video on a video player (clever, eh?), but making a QuickTime movie gives us an easier way to go back and forth in examining the motion.

The single frame from the video (right) does not show the path that the ball followed, but watching the video play clearly shows that the model's version of the motion is very different.

Right: One frame from the video

After playing around with parameters affecting air resistance, elasticity, static and dynamic friction, a new model is run that agrees much more closely with the video.

Right: Model with air resistance

The amount of physics required to do this matching process is extensive:

* frames from the video need to be measured and scaling applied,

* using the frame-rate and distances, an estimate of initial speed must be made,

* from ball diameter and linear speed, a rotational speed needs to be calculated so that the ball initially does not slip,

* mass, elasticity and friction for the ball need to investigated and set,

* air resistance needs to be set.

The more one tries to fine tune the model, the more one is confronted with the physics of the situation.

Tools to help with the analysis

There are now a number of programs around to help with the analysis of video data. One, developed by Dengler et al[16], attempts to monitor and plot trajectories automatically using a video camera. The system, called Orvico, uses an interface to a PC and tracks up to three objects determined by their colour. It is still in development and worth watching out for.

At Dickinson College, Pennsylvania, Priscilla Laws has been involved in developing a HyperCard stack called 2-D Video which facilities the measurements of the locations of objects on screen. This software is freely available (for the Macintosh). The end result is a spreadsheet file which can be loaded into Excel and plotted or analysed further. The picture below is of a ballerina. The locations of her head, her waist and knee are shown for each frame. The software also has facilities to aid in the calculation of the centre of mass of common objects (such as people!).

A screen from 2-D Video

Part 5: What's involved; what's required

Giving details of the complete process of generating videos for the kind of applications mentioned here would require an extensive talk in itself. I will give an overview and a few pointers for you to follow up, if you wish. A useful introductory reference on the area is the article by Wolf[17] in which he gives a good overview of what can be done, including detail on the technical side of digital video, frame rates, compression, CD-ROM, etc.

Overview of the process

The process of going from real-time event to a workable on-screen video is as follows:

Video the event:

A little obvious maybe! Try to get as many frames per second as possible. If you have good lighting, and a video camera that allows it, set the shutter speed to 1/1000 sec. Bright markers on the subject will help identify reference points later.

Digitise the video:

Here's the rub! You need a computer with a digitising card (also referred to as a frame grabber). It's a case of "what you pay for is what you get". A cheap card might cost $450 with editing and digitising software (eg. VideoSpigot) but it will take a fairly long time to capture each frame. Ideally you want to catch every frame, and they roll in at 25 per second! You can catch them manually, one at a time (slow), or spend more money and buy a better card (say, RasterOps 24STV at about $2000) together with something that will compress the captured frames quickly and stick them into RAM (say a MoviePac board, again $2000) and you're away (and out of pocket!). You will need plenty of memory (RAM) in your computer as saving these frames to disc is too slow. As a very rough guide, an extra 10 MBytes will allow you to capture about 4 seconds "on the fly" of full-frame-rate video. It depends, of course, on size of the final movie, number of colours and quality.

In all of the above we can make compromises. The penalty for not having the most gee-whiz digitising equipment is that you will have to be content with a lower frame-rate, smaller picture size, fewer colours, poorer quality, or a combination of the above.

Compress the video:

In order to enable the video to play back at a reasonable rate (and to fit onto your always-too-small hard disc!) you will need to use a compressor. Some of the frame-grabbing cards have hardware compressors built in, but they are not necessarily the best to use in the final video file. A variety of compressors are supplied with QuickTime, but the choice of which to use is an art! It's a matter of horses-for-courses, trial-and-error, suck-it-and-see, or any other cliché. Best advice is to talk to someone who has done it before and can advise on which might give the optimal results for the particular configuration you have.

Edit the video:

You might not need to do this. For example, if the video is to be used by students in the lab, then it probably warrants no editing. If you want to produce something to use as a part of a lesson, the you might want to edit out parts or join segments together. This simple editing of both the video and sound can be done in a cut-and-paste style using Apple's MoviePlayer. For more fancy editing (special effects, titles, superpositions, etc.) you will need to buy software such as Adobe Premiere.

Play it

A QuickTime video can be played through a large number of applications: MoviePlayer, HyperCard, even word processors have this facility.

For your efforts you will invariably end up with lots of large files on your disc and a plea to your financier for a larger hard disc!

Part 6: Where is it going?

This presentation has only scratched the surface of what multimedia has to offer today, let alone during the next few years. We are bound to hear a lot more hype--virtual reality, virtual classrooms--hence it will be up to us a teachers to sort out the good from the bad; that which promotes deeper learning from that which merely entertains.

The technology of CD-ROMs is something that must not be overlooked. Already vast amounts of material is coming out in this form. It opens up much motivating material that can enrich physics teaching. This will be especially true in areas which are often poorly served today: history of physics, effects on society, physics of technology. Instead of having to turn to a variety of books, students will be able follow these lines of study from within the one package. They will be able to integrate these aspects into their learning of physics--see a video clip of a scientist performing an experiment, and talking about it, as they read about the theory.

Multimedia should be able to present us with highly motivating resources, offer strong support for laboratory work and even change the way we teach physics. It's up to us to take it on board and make it work.

Jon Pearce is Senior Lecturer in the School of Physics and Deputy Director of the Science Multimedia Teaching Unit.

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These pages are maintained by Jon Pearce ( jonmp@unimelb.edu.au), Department of Information Systems. The opinoins on them do not necessarily reflect those of the University of Melbourne. Tel: (613) 8344 1495 Fax: (613) 9349 4596. Last update: February 14, 2007 .