UNDERSTANDING THE PHYSICS OF CHANGING MASS PHENOMENA

A.L. ELLERMEIJERAMSTEL Institute, Faculty of Science, Universiteit van Amsterdam,

1098 Amsterdam, The Netherlands

Changing mass phenomena, like a falling chain or a bungee jumper, might give surprising results, even for experienced physicists. They have resulted in hot discussions in journals, in which for instance Physics professors claim the impossibility of an acceleration larger then g in case of a bungee jumper. These phenomena are also interesting as topics for challenging student projects, and used as such by Dutch high school students. I will take these phenomena as the context in which I like to demonstrate the possibilities of ICT in the learning process of physics. Especially dynamical modeling enables us to describe these phenomena in an elegant way and with knowledge of high school mathematics. Furthermore tools for video-analysis and data from measurements with sensors allow us to study the phenomena in experiments. In this paper we discuss the actual situation of the integration of ICT in Physics Education and the latest development on this path: use of computers by students during national examinations. Finally we will present an interesting project of high school students, which demonstrates the power of ICT-tools in conducting research projects by students.

1 Integration of ICT in Dutch Education

Computers started to be used in Dutch Education in the early eighties. From 1985-1988, a government-funded project called NIVO (New Information Technology in Secondary Education) donated computers, based on Intel 8086 processors and MS-DOS, to schools. Many schools bought additional computers, so these machines became the standard in secondary schools. In addition to this hardware schools received a basic package of different software, in-service training of teachers was provided and development of educational software.

The standardisation sparked school programmes for the learning and application of information technology skills. Originally, these were mainly general skills such as using word processors, databases, and spreadsheets. In science the computer was introduced as an aid for practical work, so for computer-based data logging and modelling. This introduction acquired momentum especially in physics by two actions. The first action was the introduction by the Dutch government of computer science into the school curriculum. At the lower level of secondary education computer science was obliged for all pupils. This was a small subject, where pupils learn the basic computer skills. From 1993 extra ICT attainment targets were set for science. Pupils had to be skilled in using the computer for acquiring and processing (science related) data, and for using the computer for understanding processes (simulations and modelling). In the upper level of secondary education, the government made the choice to promote the use of information technology in all subjects instead of one new subject computer science. So they give explicit attention to concepts and/or skills related to Computer Science in the

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syllabi of several subjects, including physics. In fact already in 1989 the committee in charge of the new physics syllabus for upper secondary included the skills and concepts of computer-based data logging and modelling on the list of attainment targets. Physics was the first of the subjects were this was done, and schools received extra budgets to acquire the necessary equipment and a national project for in-service training of physics teachers has been performed.

From that time on data logging and modelling became popular in the schools. It started in physics, followed by chemistry and biology. For these activities the University of Amsterdam developed an interface (named UIA, universal interface adapter) and an integrated-software package, called IP-COACH.

The first approach to create a curriculum based on the integration of these computational concepts in physics was done in two courses (de Beurs and Ellermeijer, 1992): 1. A course ‘Process Automation’ for pupils of grade 10 (age 16). In this course

(about 20 lessons) a treatment based on practical work of information technology - from the context of ‘measurement-control-systems in daily life applications’- was chosen.

2. A course ‘Computer Applications in Physics‘ for grade 12 (ages 17, 18). The main subject of this course is the application of Information Technology to modern scientific research (on-line measurement, data processing and modelling) and the use of IT-applications in the school laboratory.When the new exam program came into operation, developments for modelling

were still underway. The government delayed the requirement of the introduction of modelling by the schools for some years. Before modelling could be introduced, it became evident that the physics exam program was over-loaded. For that reason in 1994 (WEN, 1994) the government mandated that on-line measurements, data processing and modelling must be assessed in the practical work of the school exam, rather than in the written central exams. For that reason the second course 'Computer Applications in Physics' was changed. A new course with examples of modelling was created, called 'New computer applications in physics: working with computer models of physics'.

Till the end of the nineties computers were used in science mostly for practical work or investigations. The data logging took place in science labs and the modelling in the computer rooms of the schools. In 1996 in the physics departments physics teachers and pupils used the computer for the following activities:

Table 1. Computer uses in the physics department.           

Computer uses in the physics department Ranking Uses

For making tests and worksheets 1 regular In lessons computer science (computer-based data-logging and modelling) 2 regular In lecture experiments 3 regular In practical investigations 4 regular Lessons computer science (automation) 5 sometimes

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In practical work by pupils 6 sometimes Explaining theoretical aspects 7 sometimes With exercises 9 seldom As homework 10 almost never Other 8 sometimes

But nowadays, almost all the textbooks include CD-ROMs and web sites. And national examinations include assignments clearly referring to ICT-related concepts and skills. Examples are given in Figure 1.

We can conclude, that after 2 decades of implementation activities, the use and integration of ICT in the teaching and learning process in physics education in The Netherlands has reached a rather good level. In our opinion crucial factors have been:

Consistent approach for many years Concerted action: innovation, together with facilities, teacher training AND

change of curriculum and examinationThe concluding step in this process is the actual testing of the students’ ICT-abilities during the national examination.

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Figure 1. Page from a Textbook

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Figure 2. Questions from national exams.

2 Exams of tomorrow - Use of computers in Dutch national science exams

Development of ICT examination

Exams, especially nationwide exams, have a considerable influence on the style of teaching and even on the curriculum itself. For example, various difficulties with computer algebra based assessments and examination boards banning the use of symbolic calculators in written exams have been reported as one of the main reasons why computer algebra has not penetrated (yet) in teaching and learning as much as expected by pioneers (Trouche, 2005). On the other hand, countries with national exams obviously have an innovation mechanism at their disposal. This has been put to use in the Netherlands in the last five years as part of the Research and Development programme ‘Exams of Tomorrow’.

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In the year 2000, the Dutch Ministry of Education initiated the first pilots of national science exams with computers to be carried out on an increasing number of secondary schools that volunteered to participate. From 2002 to 2006, every profile (a fixed combination of subjects) had, has, or will have at least one experimental computer exam parallel to the traditional exams ‘in writing’. During these years, the fraction of participating schools steadily increased from 0.5% to 17%.

For Physics, these exams contain 40% assignments that have to be solved with computer tools like modelling, (data) video, data processing, applets, automated control technique, statistics, and so on. One makes use of standard software like Excel (in mathematics and economics pilots) and of other more specialised, but widely available and broadly used software. The Coach learning environment falls in the latter category. It is used for computer modelling and video analysis. It is available at every Dutch school and a home version for students is available.

Based on the pilot experiences, the Dutch Central Examination Board selected physics as the first domain that has this new type of exam (60% in writing, 40% with the computer) compulsory for the whole country from 2007 onwards. Video analysis, computer modelling and electronic systems building are the computer tools that will be used here. Biology follows in 2008 and it will also use computer modelling and video analysis. From this time on, ICT applications constitute a permanent element of science exams.

All pupils of secondary education have to be prepared for these exams. They are supposed to control a number of computer tools like modelling and data processing, but also data video measurements. In order for the pupils to acquire these skills, practical assignments in previous years prove to be indispensable. Being part of the School Examination Programme, there is a natural transition from motivating, content-driven assignments to the national exam that is so important (50% of their final mark) at the end of their school career.

Points under investigation in the experimental exams were:

added value of the use of computers flexibility in content scope of ICT applications organizational and practical aspects curriculum implementation added interest and enthusiasm from the part of the students.

These points and some tentative research results will shortly be discussed in the next subsections.

The guiding policy of the Central Examination Board was (and is) the following: The project is experimental from 2002-2006 and parallel to traditional exams on

paper. Up to 2006, schools choose themselves to participate. Obligatory in practical exams with vocational subjects.

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The added value is crucial and should continuously be assessed!

With regards to the setting in which the experimental exams took or take place, the following decisions were made:

Use of standard software, video & sound, simulations, animations, web-based information.

Presentation (data, information, models, graphs, video) on screen. Questions and Answers on paper. Correction by teacher on paper or by computer.

Added value?

The following advantages of computer exams were found:

More visualization is possible. Multi-media and animations enhance and broaden the presentation of content. ICT

increases the number of possibilities for pupils carrying out measurements. Data-processing is possible. A larger range of skills can be tested: ICT skills, laboratory skills, modeling skills,

etc. Executable models with try-out mode and feedback allow for larger and more open

problem settings. Problem-solving skills can be addressed! Realistic, less ‘artificial step-by step’ problems can be given.

Figures 3 to 5 give some examples of questions of the 2004 Exam.

Figure 3. Car starting from a traffic light (present pre-vocational target group)

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Figure 4 Sahara (heat in the desert).

Figure 5. Design of a toaster.

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3 A high school student project

When finishing high school, Dutch students have to make a ‘profile master piece’ (student research project) in their last years. Profiles are groups of subjects organized according to a well defined field of social interest. There are four profiles in the Netherlands: Culture & Society, Economy & Society, Nature & Health and Nature & Technology. In the Nature profiles, usually teams of two students collaborate in creating their piece of work as an independent experimental research in a topic of their own choosing.

In 2003, Niek Dubelaar and Remco Brantjes of the Bonhoeffer College (Castricum, The Netherlands) teamed up to investigate the physics of bungee jumping, triggered by their own interest and articles on the Internet. More specifically, they were excited by the alleged ‘greater-than-g-acceleration’ of a bungee jumper in some of the published papers on the subject.

They formulated the open research question: how large is the acceleration at a bungee jump and to what degree is this acceleration influenced by the relative mass of the rope and the jumper? They used video measurements on a scale model and computer modeling as tools of investigation. Soon they realized that the mass relation rope/jumper was too low to see an outstanding result and they repeated their experiment with a larger mass ratio. They also constructed a computer model based on the theory of Kagan and Kott [2], who derived an expression for the acceleration from energy considerations. Measurements were not very accurate, but good enough to see the effect clearly and to be able to compare the results with the computer model. Their conclusion: it is really true, a > g!

They submitted their work to a national contest in student research projects organized by the University of Amsterdam, and were awarded the second price. Later, they published their results in the Dutch Physics Journal [3], triggering quite a number of reactions. Comments on the subject continued at least a year on the internet. It seemed that the whole Dutch physics community was all of a sudden playing with chains, ropes, elastics etc. There were even complaints on the level of physics teaching in the Netherlands, arguing that obviously(!) a=g and that this project proofed that the level of Physics education in The Netherlands has decreased in the last decades.

Two theoreticians from the Technical University Eindhoven [4] agreed with the findings of the students, and explained that our physics intuition is so easily fooled as we are all raised with the Galilei’s paradigm of the motion of constant masses, according to which every acceleration must be produced by a force. Naturally, a rocket is an important counterexample to this line of thought.

In summary, it is nice to see that even juniors like high school students, supported by ICT tools like video measurements to do the experiment and computer modeling to solve the differential equations, are able to evoke such a heated discussion in the

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physics community with all the misunderstandings and new creativity (like an article on the lasso paradox) that go with it.

4 ICT tools used for analyzing and understanding the changing mass phenomena

The research project ‘Greater then g acceleration of the bungee jumping’ serves as an interesting example of using of ICT in the process of learning physics. For such student investigations often the Coach 6 software environment is used.

Coach 6Coach 6 is a versatile learning and authoring environment for Science,

Mathematics and Technology Education. It integrates tools for:

Measurement - on- and off-line with interfaces, data loggers and sensors Control of processes and devices Data Video – measurements on digital video clips (capture of own video clips

included) and images Modeling (System Dynamics approach) Processing and Analysis of data.

It also offers authoring facilities to create multimedia activities which includes instructions, models, videos, images, and links to Internet and can be customized to be used by students starting at primary up to undergraduate level (age 10 to 20). Coach is often used in student investigations and research projects.

Activities of changing mass phenomena The phenomenon of changing mass during the first phase of the bungee jumping can be studied by using different ICT tools such as video analysis, data logging experiment, and modelling.

Video analysis Imagine the following experiment. Two identical blocks of wood are fixed in a clamp. One of the blocks is fixed to the chain. The whole construction hangs about 6 meters above the ground. The swivel screw holding the two blocks should be slowly un-tighten, making the two blocks starting to fall at exactly the same moment. Which block hits the ground first?

The block fixed to the chain reaches the ground before the free falling block does. By making a video of this experiment student can use the recorded material to observe the (slow) motion of the two blocks and to measure the acceleration of the falling blocks.

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Data-logging experiment A data-logging experiment gives an opportunity to measure acceleration of the falling block in a different way. An acceleration sensor mounted to the wooden block hanging on the chain is used to collect data during the fall. The measured acceleration is displayed on graphs and tables.

Modeling The Modeling environment allows creating a (graphical) model which theoretically describes the phenomenon. The model applies the second Newton’s Law for an object which mass is changing in time.

Such model can be built with knowledge of high school physics and mathematics. The result of the model can be compared to the experimental data collected in the data logging experiment (or a video measurement).

Figure 6. Coach 6 Data-logging Activity.

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Conclusions

The project of 2 high school students raised a discussion amongst professionals in Physics. This project nicely demonstrates ICT can empower students to enable advanced research activities. In fact the use of a computer has turned out to be very popular and effective during these projects. It facilitates them to perform projects that reach the level of authenticity and relevance.

In The Netherlands after 2 decades of stimulation of the integration of ICT, now students are well-prepared to use the computer for data-acquisition, data-processing, modelling and even measurements based on digital video they themselves have captured. During the physics lessons in grade 7 – 12 (age 13 – 18) they have used these techniques and become familiar. It has turned out to be very effective and important during this period the formal curriculum and recently even the mode of examinations has changed accordingly.

Figure 7. Coach 6 Modeling Activity. The experimental results are compared with the theoretical results.

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Acknowledgements

This paper is triggered by the work of two high school students, Niek and Remco, and their courage to even publish in the Dutch Physics Society Journal.

My colleagues Peter Uijlings and Ewa Mioduszewska have contributed to the paper, especially for the part about the bungee jumping activities and the Exams of Tomorrow.

References

1. Ellermeijer, A.L., Mulder, C., The approach to ICT in Science Education in Holland, In: Barton R. (ed.) Learning and Teaching Secondary Science with ICT, Open University Press, England

2. Kagan, D.T. and A. Kott, ‘The Greater-Than-g-Acceleration of a Bungee Jumper’, The Physics Teacher 34/6 (1996), p 368-373.

3. Dubbelaar, N. and R. Brantjes, Nederlands Tijdschrift voor Natuurkunde (NTvN) 69/10 (2003), 316.

4. Pasveer, F. and W. de Muynck, NTvN 69/12 (2003), 3945. Mioduszewska E., Ellermeijer A.L., (2000). Authoring environment for multimedia

lessons, In: Pinto R., Surimach S. (ed.) Physics Teacher Education Beyond 2000, proceedings of the Girep conference 2000, 689-690, Elsevier.