USING SERIOUS GAMES AND COMPUTER SIMULATIONS IN AN AUTHENTIC CONTEXT FOR PHYSICS EDUCATION

 
USING SERIOUS GAMES AND COMPUTER SIMULATIONS IN AN AUTHENTIC CONTEXT FOR PHYSICS EDUCATION
USING SERIOUS GAMES AND COMPUTER
      SIMULATIONS IN AN AUTHENTIC CONTEXT FOR
                 PHYSICS EDUCATION

Jeremias Weber, André Bresges
University of Cologne, Germany

Abstract: Previously, a Serious Game was used in the school lab of the University of
Cologne to educate students in the age between 12 and 16 about the consequences of
radical climate changes. This was embedded in the educational context of the whole lab.
The findings were generally positive and motivating. Now, serious games and computer
simulations are used in an effort to get students in the age between 16 and 18 to better
understand the physics of cars and their own skills as drivers. This is embedded in an state-
wide intervention program designed to further reduce the number of deaths in road traffic,
named CrashKurs NRW. This is an intervention program, adapted from a british program
and extended by Prof. Bresges of the University of Cologne. It is composed of a stage
show and the educational follow-up program. Where computer-based learning fits into the
latter will be discussed in the presentation.
At first the terms „Serious Game“ and „Computer Simulation“ will be defined. The general
benefits and disadvantages of the use of Serious Games and Computer Simulations will be
discussed and the design and findings of the preliminary study in the school lab will be
shown. A quick overview over CrashKurs NRW will be provided. Which specific programs
are being used and in which way they are being used will also be described. Because of the
importance of a constant improvement of this design based intervention program, the
evaluation of the exact benefits will also be described and the current findings will be
presented. The conclusion of the presentation will consist of an overall summary and a
description of the possible opportunities to improve the current intervention program.

Keywords: Serious Game, Design-Based Research, game-based learning, students lab

DEFINITION OF TERMS
When talking about computer-based learning, we must distinguish between the various
methods of using computers in school.

One method is the use of learning games, as done by Egenfeldt-Nielsen (2007). Learning
games have a mix of elements from playing and learning. Both elements are clearly
separated and distinguishable. In this games, elements of playing are used to reward the
player or student for successful learning. For example, after solving a mathematical
question correctly, a short segment starts where the student has to fight flying objects.

Especially in physics, but also in other STEM classes, computer simulations (Geban, Askar
& Özkan, 1992) are used frequently, e.g. simulations of light propagation in prisms or
simulations of nuclear reactions. The element of playing in these simulations is only
„playing around“ with the scientific variables. There is no leisure aspect in these
simulations. Computer simulations are often used to show aspects of the world that are
otherwise not presentable in school.

Both of this methods are used for quite some time and in both the more important part is
USING SERIOUS GAMES AND COMPUTER SIMULATIONS IN AN AUTHENTIC CONTEXT FOR PHYSICS EDUCATION
always the scientific content. As Prensky (2001) explained, in Serious Games, the element
of playing is seemingly more important and is not just used for repetition or exercises. The
term „stealth learning“, used by Sharp (2012) and de Freitas (2006), describes, what
Serious Games should do really: Teaching the subject matter in a covert way by
incorporating subject knowledge in the game itself. Other people use this method of
computer-based learning as well. For example, Crews (1997) calls it an „Anchored
Interactive Learning Environment“. Still, in this article, the term „Serious Games“ will be
used. Examples for this kind of computer-based learning would be „Food Force“ by the
WFP (http://www.wfp.org/get-involved/ways-to-help) or „Bridge Builder“ for Mechanical
Engineering.

USING SERIOUS GAMES IN SCHOOLS
Serious Games, if they are to be used in school, have potential benefits, but there are also
constraints to be observed. This is true in both directions: Serious Game and school lesson
should fit together.

Constraints and framework
First of, a „meaningful learning context“, as talked about by de Freitas (2006) has to be
constructed. This means, the Serious Game should not be stand-alone, but instead be
imbedded in a learning environment. For example, if a climate simulation would be used,
the position of the sun should not only be used in the simulation, but also in classroom
experiment. Also, conducting and observing real experiments in the classroom could help
to overcome obstacles in the game. Without this „meaningful learning context“, a long-
term effect of the game is doubtful.

Also, a Serious Game has to motivate the student to progress further in the game and
experience new situations. Without this motivation, students will not try new theories or
unfamiliar situations, as shown by Eysink, Dijkstra and Kuper (2001) and Schauble, Glaser
Duschl, Schulze and John (1995). Commercially successful games have already solved this
step by developing a narrative, which guides and motivates the player. For example, the
game could prompt increasingly complex questions about physics, which follows a story
about a young inventor as he tries to establish a successful factory. This is the approach of
the game „Genius Physik“ from Cornelsen Verlag.

Another important task is to ensure that the medium „computer“ doesn‘t get undue
attendance. If, for example, classroom experiments are part of the lessons and the students
rather want to play the Serious Game, measures have to be implemented to restore the
proper balance. These measures can be, for example, the requirement of the completion of
certain experiments before the student can progress further in the game. Without this
balance, it is possible that the students learn nothing from the use of computer-based
learning.

Benefits of the use of Serious Games
This framework also provides a few benefits by itself. The „meaningful learning context“
can also be different classroom experiments, which are then also linked with each other by
the game itself. Also, in this way, students can experience a specific subject from various
USING SERIOUS GAMES AND COMPUTER SIMULATIONS IN AN AUTHENTIC CONTEXT FOR PHYSICS EDUCATION
angles, which is in itself a benefit.

The great computing power of modern computer systems can also be used to simulate very
complex situations. In this way, the success in the game can be dependent on a great
number of factors and variables, which are all linked and explained by classroom
experiments. Such complex situations are getting more important every year, but according
to Dörner (2003) they are still not understood clearly by many people.

Geban et al. (1992) observed, that the starting motivation of the students to use Serious
Games is very high. It was also observed by Weber (2011), that by using computers and
computer-based learning, a teacher could overcome learning obstacles in his classroom.

Especially in physics a great amount of new terms are constantly introduced. As Merzyn
(1998) said, this is one of the reasons for the difficulty of the subject in school. In
commercially successful games, this is also the case, but players are learning the terms
much faster and with greater intrinsic motivation. For example, in the popular game
„World of Warcraft“, a player has to know about „aggro mechanics“ (to draw the attention
of the computer-generated enemy) to properly cooperate with his fellow players and to be
successful in the game. In the same way a player has to understand the ballistics of various
weapons in shooting games or the language of car races and car mechanics in car racing
games to be successful in this games. Correct learning and using of all this new terms will
be rewarded by peer admiration and success in the game. This can also be used for the
learning of terms of the specific subject.

Conclusion
It can be said, that Serious Games have constraints but, if used properly, can also provide
many benefits for learning. At this point, it seems promising to use Serious Games in
school, as the potential benefits seems to outweigh the potential costs.

USE OF A SERIOUS GAME IN A STUDENTS LAB
The students lab of the University of Cologne
The aim of the students lab of the University of Cologne is to directly teach different
STEM subjects to high-school students. Normally, the only connection between a
university and high school is indirect. In the students lab, high-school students in the age
bracket between 12 to 16 can conduct various experiments. They are instructed by trainee
science teachers, which can experience high-school students for the first time themselves.
But aside from a common theme, „climate“, no links exist between the experiments in the
students lab and the experiments are not very complex. Also, the greenhouse effect is only
talked about, not shown.

So, three tasks were identified:

a. To create a link between the experiments

b. To show complex interrelations of the climate system

c. To demonstrate the greenhouse effect
USING SERIOUS GAMES AND COMPUTER SIMULATIONS IN AN AUTHENTIC CONTEXT FOR PHYSICS EDUCATION
Solving the tasks with a Serious Game
A Serious Game could be used to solve these three tasks. To show this, we have to look on
the second chapter.

As said before, a „meaningful learning context“ is needed for the use of a Serious Game. In
the case of the students lab, this context is not only available, but it is also desirable for the
Serious Game to be linked to the other experiments in the lab. This could serve as a link
not only between the game and one experiment, but the game could link to different
experiments and so link all experiments together.

To show complex interrelationships, computer systems are used constantly. As shown
previously by Dörner (2003) in an originally psychological evaluation, complex
simulations can lead to a learning success in the specific area of the complexity. With this
in mind, a proper designed Serious Game could solve the second task.

Demonstrating the greenhouse effect in an experiment is not easy. The resulting
temperature change can be shown with a digital thermometer, but more impressive would
to show the results, like vegetation change. To achieve this, you could demonstrate a
change of environment variables by the player (e.g. temperature, position of the sun,
precipitation) and the resulting change in the environment (e.g. clouds, rain, sun,
vegetation), calculated by a computer, in a Serious Game.

Use of a Serious Game - Technical and scientific aspects
To create a Serious Game, we had to choose a specific game engine and a certain
geographic background for our climate changes. Programming held an important place in
the design process and we also had to look upon the physical aspects of the targeted
subject.

Game engine and geography
We used a game engine called „CryEngine Sandbox Editor“, a game engine for modern
computer games. This allowed us to shape a very realistic world with moderate
programming skills. The already implemented tools and animations allowed us to
demonstrate the environment changes without needing to implement new elements in the
program. The programming language was also intuitive to learn.

Geographically we choose the island Helgoland as a basis for the simulated island. An
island was chosen because natural barriers exist already to limit the student‘s radius of
exploration. Helgoland is a biologically interesting island in itself, but it could have been
any other island.

Physical model and implementation in the Serious Game
As we choose a certain model for our computer simulation, we elected to gloss over certain
aspects. The following model is not scientifically correct, it doesn‘t differentiate clearly
between the global greenhouse effect and the local vegetation change. This is still a topic
of ongoing research and very complex to calculate even for modern computer simulations.
So it was deemed to complex to implement or explain to high-school students. A
scientifically correct explanation would also be beyond the scope of the students lab.
USING SERIOUS GAMES AND COMPUTER SIMULATIONS IN AN AUTHENTIC CONTEXT FOR PHYSICS EDUCATION
The proposed climate model aims to link the position of the sun (shown as an angular
degree above the horizon) to the temperature. This is done by multiplying an arbitrary
amount of energy, which should represent the overall energy of the sun, with the sinus of
this position to get the amount of energy which impacts this specific area, the radiated
energy. From this amount, a certain amount of energy gets subtracted to represent the
energy that is radiated away from the earth. The correlation between energy and
temperature was defined in this way: If the sun has a position of 90° above the horizon, the
temperature is around 27 °C and if the sun has a position of 15° above the horizon, the
temperature is around -5 °C.

The relation between absorbed energy and temperature follows the Stefan-Boltzmann law
(P~T4). This is important for the introduction of the greenhouse effect as shown later. The
virtual temperature is then divided in three temperature ranges, the middle range goes from
5 °C to 18 °C.

In the same way, the precipitation is divided into three states: No rain, little rain, and heavy
rain. This is linked to the cloud cover in the game. The greenhouse effect is then again
linked to the amount of clouds. More clouds are responsible for reducing the amount of
energy that is radiated away from the earth so the temperature will be higher. For that
reason it is important to use the aforementioned energy amounts.

By combining the ranges of precipitation and temperature, nine possible states can be
found which are then linked to a specific vegetation zone:

                     T < 5 °C           5 °C < T < 18°C              T > 18 °C
      No rain        Polar region       Subtropical dry forest       Subtropics
      Little rain    Cold temperate Temperate                        Warm temperate
      Heavy rain     Taiga              Subtropical moist forest     Tropics

The environment can be changed by the students by walking their game avatar near so
called proximity triggers in the game. They work with first two, later three triggers. The
first two triggers are responsible for changes in the position of the sun and the state of rain
respectively.

Figure 1. Exemplary screenshot of the sun position trigger
The third trigger is at the start both hidden and not active. After activation by the students,
it triggers the aforementioned greenhouse effect. A screen message and a rapidly changing
temperature inform the students about that.
The calculation of the temperature is done with a Flowgraph and follows the described
model. An example can be seen in the following picture.

Figure 2. Exemplary screenshot of the Flowgraph for the rain calculation

Use of a Serious Game - Didactic concept

To use a Serious Game in a beneficial way, the didactic concept has to be formulated
before the implementation. Aside from the previously described simplifications to the
climate model, two aspects were important: How to use the Serious Game in the context of
the students lab and which role should the tutor play?

Didactic Concept: A stage model
The concept that seemed to be fit best was a staged concept. In the four stages, the students
should learn more and more about the game and finally master it completely.
The first stage is called explorative stage. In this stage the students should master the
principal elements of the game. They have to learn how to control their avatar and should
explore the simulation for the first time. In this stage the students are left without an
explanation about the goal of the simulation or how to use it. This is intentional to not set
up artificial borders for their creativity.
The second stage, called instructive stage, begins without a clear distinction to the first
stage. After a few minutes, the students would begin to ask for directions or would be
clearly lost, so the tutor should set goals for the students or explain a few basic control
mechanisms. The goal of this stage is to give the students knowledge about the placement
of the triggers and to give them first goals. This is done by tasking them with phrases like
„Make a trip to a tropical region“. This task has to be translated by the students in certain
trigger settings (the tropical region is very warm and wet, for example) and then the
students should set the environments variables accordingly.
The third stage is started after the students have the desired level of knowledge about the
game world and the game controls. This stage is called integrative stage, because now the
students have to integrate the other experiments of the students lab in their experience with
the Serious Game. The tutor asks them to examine the other experiments and to try to
understand how they relate to the Serious Game. In the current circumstances of the
students lab the students can not conduct the experiments at this time because other student
groups are experimenting at the same time. After their examination it is important that the
students reason for every experiment why it is connected or not connected to the Serious
Game.
The fourth and last stage begins with the activation of the greenhouse effect in the
simulation. The tutor directs the students to the third trigger and then discusses with the
students the changes in the environment. After that, the students are tasked to set the
environment variables to the same values as before. In this way, the students begin to see
the massive changes done by the greenhouse effect, even if the changes at first seem minor.
Intentionally there is no discussion about ecological implications because the students are
now prepared to discuss such questions among themselves.
All experiments in students lab are currently arranged so that the groups rotate after 45
minutes. In this timetable the four stages have to fit. The first and second stage take around
20 minutes, on third of that is normally reserved for the first stage. The integrative stage
takes 10-15 minutes and the final stage takes the remaining 10-15 minutes.

Role of the tutor
The previously mentioned tutor has a difficult role. The tutor assigns tasks and guides the
students but at the same time he should not detract from the experience of exploration and
should not solve the problems for the students. He has to act more like a mentor than a
teacher and only be present when serious obstacles arise. In this way he is comparable to
the helping figures of commercial computer games.
The tutor should always facilitate the free exploration of the game. Compared to classic
classroom experiments, no safety measures have to be taken in a Serious Game. The only
constraint in this special case is the maximum time available for the experiment.
If less time would be available, it is certainly possible to control the students better and
guide them faster through the game. But such a strict control has been shown to be
detrimental to the learning success of students (Crews et al., 1997, p. 13) so it should be
done only when necessary.

Findings

After the implementation of the Serious Game, observations were made and the students
took a survey. The observations were not structured but mostly based on reports from the
tutors and oral feedback by the students. The survey was done three times with varying
questions. All evaluative methods had to be completed in a very short time so they are
questions left. (Weber, 2011)

Group observations
The observations are more about the students behavior while playing the game and aimed
at the improvement of the didactical concept.
One example for that is the change of the integrative stage. That students reason about the
correlation of experiments and the Serious Game was done after observing that, if the
students are not required to do so, they didn‘t properly examine the experiments.
In this observation a high motivation to play the game could be seen. It was not clear if the
reason for that is more the medium or the content of the game.
The communication between the students improved not only in the area of mutual support
but they also used more correct terms to describe the climate and the changes in the
environment. Especially interesting was, that the students could identify the greenhouse
effect by analyzing its implications of the game world. (Weber, 2011)

Survey results
The students had to answer tests. They were given to the students before and after playing
the Serious Game. The second time they should reevaluate their first answers and correct
their previous answers. The test had to be improved during the survey so aside from the
first question they are not easily comparable. (Weber, 2011)
In the first question the students had to construct a Mind Map around the term climate.
This was done to ascertain how many terms they know and how many terms they learned
by playing the game.
The third questions asked them to link various terms together. This question was designed
to examine what students learned about the interrelation of these terms. The number of
connections was counted before and after the treatment.

Table 1
Averages between the surveys (Weber, 2011)
                                             survey 1   survey 2   survey 3   average over the surveys

       Average number of concepts in the     11,0       8,5        6,9        8,8
       concept map

       Standard deviation of the number of   3,2        1,6        1,1        1,3
       concepts

       Average number of the increase of     3,4        1,3        0,8        1,8
       concepts

       Standard deviation of the increase    2,7        1,4        1,2        1,1
       Average number of connections         3,1        6,0        6,5
       Standard deviation of the number of   0,3        1,3        1,5
       connections

       Average number of the increase of     0,1        2,1        1,2
       connections

       Standard deviation of the number of   0,3        1,1        0,9
       the increase

The results showed a small increase in known terms in all surveys and in an overall
average it was shown that this increase is greater than the standard deviation. If we look at
the third question in the last survey, we see that there was also a small increase of the
number of connections, which is still greater than the standard deviation.
The survey should be improved in the next iteration, but they can be used to start the next
cycle of the design-based-research cycle, as explained by Reinmann (2005).

Conclusions
It can be concluded that the use of this Serious Game is very motivational for the students.
But for further use in, for example, physics lessons, the climate model should be more
scientifically correct.
The didactic concept of this Serious Game should be improved as well. The tasks of the
tutor should be structured more clearly and more along a specific narration like in
commercial games. In this way, it could be possible to minimize the impact of the tutor
himself.
More important but at the same time more difficult is a changed context. For a further
improvement of this Serious Games, but also with other Serious Games, the classroom
experiments should be tailored more specifically to the game. In this way, students could
draw important conclusions about the game by conducting an experiment.
Still, the development of this Serious Game was important. It showed the problems of
proper designing a Serious Game but at the same time it gave a look on possible benefits of
such games.

USE OF SERIOUS GAMES IN AN EDUCATIONAL FOLLOW-UP
Motivated by the aforementioned conclusions, it was deemed possible to use a Serious
Game for the educational follow-up program of the intervention program CrashKurs NRW.
CrashKurs NRW
CrashKurs NRW was originally developed in Staffordshire in England was implemented in
high-schools of the federal state North Rhine-Westphalia in Germany. It is a stage show,
where police officers, paramedics and firemen describe their personal experience with
severe accidents and the repercussions for injured people and their families. For example,
one of the goals is to describe how the use of cell phones can lead to a car crash.
Bresges (2011), Hackenfort (2013) and Janssen (2011) evaluated this stage show and found
improvement possibilities, especially in the area of the educational follow-up program.
As described Weber and Bresges (2013), to improve this stage show, one opportunity
would be to design a seemingly realistic computer simulation where students can
experience the seriousness of distractions.
A racing game as a Serious Game
The Serious Game was designed to let the students experience the impact of distractions
during driving in a safe and controlled environment. To do this, the didactical concept was
modeled, using the experiences with the concept described before:
In a first stage, the students are tasked to explore the possibilities inherent in the game and
train themselves to control it properly. To do this, the students would be separated in small
groups and should compete with their group members in the game. Because a racing game
was used, their competition centered on a good lap time.
After the teacher is sure that the students are trained properly, he assigns the students a new
task. Every group has to list various distractions in traffic and assess their severity. They
have to present their lists to the other student groups and explain their respective reasoning
for their severity assessment.
In the third stage, every group has to simulate the distractions on their list while playing
the racing game again. For example, one student plays and the other students is talking to
her and asking her questions to simulate a co-driver. Again the students have to compete
against each other for better lap times.
During the final stage the students should discuss the impact of the various distractions on
their driving skills. In this stage the students should also reevaluate their own assessment
from the second stage. The end of this stage is a discussion how transferable this all is to
„real“ driving.
Pilot study
A first pilot study was done to evaluate this didactic concept. The students were chosen
from a vocational school in cologne, one day after the stage show of CrashKurs NRW.

Figure 3. Student group in the first stage
As seen here, all members of the student group participate in the first stage, not only the
one who plays at the moment.

Figure 4. Students in the second stage

Figure 5: Students in the third stage
This student group discusses first about the distractions and then tries them out. In this
case, the student is one of a few licensed car drivers in the class and is still not able to
control the game and at the same time to use the cell phone as a navigational aid.
Oral feedback of the students showed that they liked the concept very much. More
important, their statements after conclusion of the lesson indicated appropriate conclusions
about distractions. For example, many students felt in the second stage, that conversation
with a co-driver is less distracting than calling someone on the phone. After the third stage,
they rated the severity of the distraction by a co-driver much higher. Using car radios or
navigational aids were similarly found to be underestimated by the students. Part of the
feedback centered on the second stage, the students felt that their task was not clear
enough.
Further evaluation
After completing this first cycle of the design-based research process, we will begin with
the next cycle and implement all improvements derived from students feedback and our
own observations.
To then evaluate the impact of this lesson further, a formal evaluation will take place. This
evaluation will be modeled after the evaluation done by Hackenfort (2013) and will
concentrate on the opinions of the students about distractions.

CONCLUSIONS
Serious Games have a place in education if properly introduced and used for a fitting
purpose. A Serious Game is not always useful and if it is used, teachers should always be
aware of the constraints. At the same time, if they are used properly, Serious Games can
have a great benefit for teachers. As shown in the two examples, they can open new
avenues for teaching and learning.

The most important finding was the importance of the didactic concept that frames the
Serious Game. Companies can program Serious Games (like in the second example) but
the usefulness is directly linked to the quality of the didactic concept.

So it can be concluded, that even if Serious Games would be an important tool for
education, they are at the same time dependent on teachers and researchers. And for that
reason, future research in this area is needed to identify more uses of Serious Games and to
support teachers who want to use a Serious Game.

REFERENCES
Bresges, A. (2011). Prozessevaluation des Crash Kurs NRW. Bericht der
         wissenschaftlichen Begleitung (in German). Düsseldorf, Germany: Ministry of
         the Interior.
de Freitas, S. (2006). Learning in Immersive Worlds. Bristol: Joint Information Systems
         Committee. Retrieved from:
         http://www.jisc.ac.uk/media/documents/programmes/elearninginnovation/gamingr
         eport_v3.pdf
Crews et al. (1997). Anchored Interactive Learning Environments. International Journal
        of Artificial Intelligence in Education, 8.
Dörner, D. (2003). Die Logik des Misslingens: Strategisches Denken in komplexen
        Situationen (in German). Reinbek bei Hamburg, Germany.
Egenfeldt-Nielsen, S. (2007). Att skapa ljuv musik: Det pedagogiska anvandandet av
        datorspel (in swedish). In: Jonas Linderoth (Ed.), Datorspelandets Dynamik
        (pp.185-206), Lund, Sweden: Studenttliteratur. Retrieved from:
        http://egenfeldt.eu/papers/sweet_music.pdf
Eysink, Dijkstra and Kuper (2001). Cognitive processes in solving variants of computer-
        based problems used in logic teaching. Computers in Human Behavior, 17(1), 1-
        19
Geban, Ö., Askar, P., Özkan, Ï. (1992). Effects of Computer Simulations and Problem-
        Solving Approaches on High School Students. The Journal of Educational
        Research, 86(1), 5-10
Hackenfort, M. (2013). Evaluation of a crash prevention program with fear arousing
       proposal. Zeitschrift für Verkehrssicherheit 59(3), 155-160
Janssen, A. (2011). Die Nachbereitung des Crash Kurs NRW im Unterricht: Entwurf eines
         Unterrichtkonzeptes mit Ansätzen zur qualitativen Analyse der
         Unterrichtswirksamkeit. Cologne, Germany
Merzyn, G. (1998) Sprache im naturwissenschaftlichen Unterricht, Teil 1-3 (in German).
        Physik in der Schule, 36, 203-205, 243-246, 284-287
Prensky, M. (2001). Digital Game-Based Learning. New York, USA: McGraw-Hill
         Companies.
Reinmann, G. (2005). Innovation ohne Forschung? Ein Plädoyer für den Design-Based-
       Research-Ansatz in der Lehr-Lernforschung (in German).
       Unterrichtswissenschaft 33(1), 52-69
Schauble, Glaser, Duschl, Schulze und John (1995). Students' Understanding of the
        Objectives and Procedures of Experimentation in the Science Classroom. The
        Journal of the Learning Sciences, 4(2), 131-166
Sharp, L. (2012). Stealth Learning: Unexpected Opportunities Through Gaming. Journal
        of Instructional Research, 1, 42-48
Weber, J. (2011) Integration eines computergestützten Klimamodells in ein
        fächerverbindendes Schülerlabor mit dem Rahmenthema: „Unser Raumschiff
        Erde“ (in German). Cologne, Germany,
Weber, J., Bresges, A. (2013). Authentische Probleme für authentische Aufgaben im
        Bereich der Verkehrserziehung (in German). Proceedings of the Spring Meeting
        2013 of the German Physics Society. Retrieved from http://phydid.physik.fu-
        berlin.de/index.php/phydid-b/article/download/465/605
You can also read