Diapositiva 1

1
A research based proposal on teaching learning
physics in the context of Judo
Marisa Michelini, Alberto Stefanel esearch Unit
in Physics Education, niversity of Udine, via
delle Scienze 206, 33100 Udine,
Italy alberto.stefanel_at_uniud.it
The fact that lt Vz gt 0 m/s for the first 0.68 s
tells us that the right hip remains at the same
level of advanced standing when U start the
rotation, even when U has the right foot in
contact with the ground, the stage of loading on
the spine of T.
This highlights one hand that the body of U-turns
around an axis passing approximately through the
right hip, the other that the center of U, as if
they might not know the exact location of the few
elements available in first three phases of the
throwing technique analyzer is appreciable
vertical movements. The body of substantially U
moves forward by inertia. Only a slight
acceleration produces a small increase in forward
speed U in the horizontal direction (along the
y-axis). It is only the last stage that the body
of U moves vertically, initially with a forward
motion oblique to 75 , then gradually more and
more vertically, with average acceleration equal
to 8.2 m s-2.
Introduction Sport offers many opportunities to
evidence how physics constructs models of
real-life phenomena starting from first
principles (Armenti 1992 Goff 2004 Bradamante
et al, 2004 Heck, Ellermaijer 2009) selecting
aspects to be analyzed and the theoretical
framework in which these aspects are included
using the formal tools to describe in detail only
those aspects (Sperandeo, Sassi 2002) providing
the ability to interpret processes and predict
the evolution of the phenomena under observation
(Bednar et al 1991 Hesteness 1987, 1992,
Michelini et al 2002). The modeling activities
and opportunities, that are provided by the new
information and communication technologies
(Bednar 1991 Aiello et al. 1997 Thornton,
Sokoloff 1999, Michelini et al. 2002 Heck,
Ellermaijer 2009), become powerful teaching tools
through which to give answer to many difficulties
in teaching and learning physics at school. In
particular it is well known that in the context
of mechanics many students learning difficulties
in linking real phenomena and scientific
knowledge (McDermott et al 1987 Duit 2009) are
related to the reductionist educational
approaches in mechanics, that stress on the
rectilinear uniform motion and on the motion of a
material point, without giving to the students
the instruments to understand what part of real
phenomena it is possible describe with this kind
of models and what kind of modeling process is at
the base of physics interpretation of the natural
phenomena (Michelini et al 2002). The challenge
is therefore to change the perspective with which
to teach physics, from situations, that students
recognize as real, close to their everyday life,
such as those offered by sport, and show how
physics, in relatively simple way, is able to
describe complex phenomena basing on a few
principles core. Here we present the main points
of a research based educational proposal aims to
introduce physics at secondary level using judo
as context to explore interactions, energy
exchange, body motion.
The dynamics of motion. What forces act to
produce the observed motion? What resultant do
they have? What is the resultant momentum of
forces? The acceleration of fall is less than
that of gravity and also is not directed
vertically, showing how the interaction between U
and T will continue even in the last phase of the
fall. The forces, that T apply to U, have a not
null resultant in the y direction (horizontal),
and these do not work, in average, against the
gravitational field and determine a moment of
forces that produces only the rotation of the
body of U. The body mass of U is 80 kg. The
resultant of forces acting horizontally is
therefore approximately 90 N in the first three
phases, and 400 N in the first part of Phase IV
(in which there is still a forward acceleration
of U).
Shoulder Linear speed
Shoulder Angolar speed
Shoulder Angolar speed
The rotational motion of the body of U can be
modeled with that of a rigid body (a rigid
cylinder M 80 kg, h 1.6 m, r 0.13 m and a
inertia moment I 17.4 kg m2), subject to the
action of a moment of force constant which
determines a rotation around a transverse axis of
gravity with constant angular acceleration of 14
rad s-2.
Hip vx
Research questions. The present contribution
aims to answer the following research
questions How can we describe, in terms of
physical quantities and physical models,
processes as complex as that of a judo throwing
technique? That is What aspects of a complex
action, such as a projection of Judo, can be
described by the simplest models that physics can
build? RQ2) What can say us physics on judo?
That is What physical principles are
particularly evident in the dynamic action of
judo and which of these can be effectively
offered in secondary school? RQ3) What tools and
ICT can be used to build an educational path?
Hip vy
Fig.6. Linear speed and angular speed fo the
shoulder
From the second law of dynamics Cardinal (M I
dw/dt), we obtain that the moment applied to the
cylinder has to be 244 N m. It can be generated
by a couple of forces of 163 N applied at the
ends of each cylinder, as in phase II, namely a
couple of forces of 326 N, applied in the center
of gravity and the other to one end of the
cylinder, as actually occurs in the phase III
loading on the back of U of T).  
The main points of the educational path. Here is
presented a proposal of teaching activities,
taking as examples only two throwing techniques
between the over hundred encoded ones in judo
the seoi-nage and the okuri-ashi-barai.
Fig.7. Components of the linear speed of the hip.
From the second law of dynamics Cardinal (M I
dw/dt), we obtain that the moment applied to the
cylinder has to be 244 N m. It can be generated
by a couple of forces of 163 N applied at the
ends of each cylinder, as in phase II, namely a
couple of forces of 326 N, applied in the center
of gravity and the other to one end of the
cylinder, as actually occurs in the phase III
loading on the back of U of T).  We observe that
once the action has been initiated, the force
applied with the hands by T cannot vary
appreciably, because the distances do not vary
substantially between T and U. The increase in
the force couple applied to be mainly due to the
thrust, which T applies to the U with his back.
This confirms what is found in the literature
about the action of T on U (Blais et al . 2001).
1. The throwing techniques of judo and the choice
of items to look at What characterizes a combat
sports such as judo, compared to other sports
contexts, is that in a typical throw technique as
those illustrated in the figure 1, the two
athletes Tori (T below) and Uke (U below) always
interacting one with the other.  In the context
of judo, the two interacting systems (U and T)
are always clearly identified and separated and,
therefore, the interactions between them are
always identifiable, even if it is not easy to
directly measure the forces in the interaction.
Instead, you can directly measure from movies the
kinematic quantities of the athletes as suggested
in the literature (Sacripanti 1996, Blaise et al
2002) and to derive from this information, the
dynamics of interacting systems. The choice, that
was made, is to focus attention on the motion of
U to reconstruct, through simple models, the
dynamic conditions that make it possible.
T
U
U
All the action that T makes for projecting U
executing seoi-nage, then resolves in the
rotation of the U body without changing
appreciably the center of mass height, and then
accompanies him on the final fall to the ground.
Performed the dynamic analysis, a question
remains why the action of judo is so efficient
in producing its result? How does a person of
little mass to throw a massive person to the
ground?  To fully understand the action of
seoi-nage is important to stress the following
two important aspects of the crucial phase of the
technique, which is when we move from Phase I to
Phase II. The first concerns the way in which T
can be applied effectively forces the time needed
to start the rotation of the body of U. In the
figure (Nomura 1996) are stylized U and T. T
applies a force with his left arm on his right
arm from a standing position the first U (I) and
squat (II). This, as mentioned earlier, is used
to lower the center of mass of T compared to U
and let the load on his back. This movement,
accompanied by a large traction toward the front
with his left arm, allows T, to equal the applied
force, to apply the greatest possible time to U,
when it is loaded on the back (III). A simply
simulation effectively realize this point. The
second issue is how to make efficient the
coupling between the T and U, so that, when the
same force applied, it has the greatest possible
increase of angular velocity of U (this is a very
important factor in determining 'effectiveness
not only from a competitive point of view, but
also in terms of its formal correctness). As we
observed the motion of the abdomen of U until it
has already entered into rotation, continues to
be in a straight line with a speed that
increases, even if only slightly in the direction
of motion of U. To achieve this it is necessary
that T acts with forces that are in phase with
the movement of U. In other words, it is
necessary that you implement some sort of
resonance between T and U. It is well known in
physics that the resonance has an essential role
in coupling systems. Judo can provide an
opportunity to understand in the context of sport
in what is the resonant coupling of two systems
and because it enables an efficient transfer of
energy, momentum and / or angular momentum. We
will not dwell further on how this coupling is
realized in the case of seoi-nage, preferring to
discuss analyzing another throwing technique the
Okuri-ashi-barai.
T
Figure 1From http//www.intjudo.eu/
THE MOVEMENT OF THE LEVER
2. Rotate a body by applying a force couple the
Seoi-nage In a typical technique of judo, for
example the seoi-nage, the basic texts on judo
highlight the importance that the center of mass
of T is lower than that of U, so that the action
of force couples applied to U from T to be
effective, as in the reported illustrations of
the text of Toyokazu Nomura, Olympic champion in
Munich 1972 (T. Nomura 1993).
Figure 3 From Nomura 1996
The description of the phenomenon. Through
analysis of a video, that here is performed using
image processing tools that are available on all
PCs, as shown in other work (Michelini, Stefanel
2010), it is possible to recognize four elements
of discontinuity the initiation of movement
where U and T begin to move on the mat at the
start of Kuzushi, in which T pull U and start to
rotate the beginning when U comes in contact
with the back of T the beginning of phase where
U is detached from the back of T and falls on the
back. This motivates the division of the motion
in four phases, which are described referring the
motion to a defined reference system as shown in
the figure 4
Fig.8. The phases of de ashi Barai
3. Resonant coupling of two systems
Okuri-ashi-barai
The same discussion made for the seoi-nage
technique can be repeated in the case of
Okuri-ashi-barai. We had chosen to analyze the
motion of the left shoulder of U and the knot of
his belt, which lies a few inches below her
navel. From the analysis of motion of the points
considered, we recognize three phases
Fig.9. The trajetories of the Shoulder and of the
belt knot.
Figure 2 From Nomura 1996
Phase I (from 0.00 s to 0.40 s) - U moves with
approximately uniform rectilinear motion along
the y direction, T back with approximately
uniform motion and makes a rotation around an
axis parallel to z. Phase II (from 0.40 s to 68
s) - U moves rotating, as results of the
composition of two rotations, of which we
consider only one around an axis parallel to x
through the support point of the right foot of U
T is lowered, remaining in a fixed point on the
xy plane and bringing its center of mass low as
possible compared to that of U, as described
before.
Phase 1 (from 0.00 to 0.40 s) the horizontal
displacement, with the classic vertical
oscillation due to the distance (emphasized here
by the fact that they are skipping the
side). Phase 2 (from 0.40 to 056 s) T and U are
strongly coupled. The basin of U continues almost
uniform horizontal motion while the body of U
begins to rotate around an axis passing
approximately through his left shoulder that is
nearly stationary.Phase 3 (0.56 -0.92 s) U
describes a motion almost vertical drop to the
mat.
In Phase 2, the rotational motion of U is done
with average speed of 0.3 rad s-1, the first part
of phase 3 with angular velocity 10 rad s-1. The
acceleration of vertical drop is on average 0.76
m s-1.Although the Okura-ashi-barai is a
technique very different from seoi-nage, also in
this case a force momentum is applied on U that
rotates with angular acceleration of 19 rad s-1,
higher than the previous case.
Figure 4 Seoi-nage phase I
Phase III (from 0.68 s to 0.76 s) U rotates
around an axis parallel to x, T moves in the z
direction rising slightly while turning the torso
around a vertical axis  Phase IV (0.76 s a 1.08
s) - U rotates around an axis parallel to x,
passing approximately through the center of mass.
This axis in turn rotates around an axis parallel
to the x and y goes down T only moves in the z
direction rising.
We simulate the motion of U with that of a
cylindrical rigid body is obtained which is
necessary to apply a resultant moment of 330 N m
(obtained with a pair of forces of 206 N applied
at the ends of the cylinder).
z
U T
The essential and more evident aspect of this
throwing technique is the resonant coupling
between T and U. To understand this action we can
analyze how a pendulum can effectively transfer
energy and momentum to another pendulum of
different lenght, as shown in the sequence
extracted from a simulation realized in the
Interactive physics environment
(http//www.design-simulation.com/ip/index.php).
When the first pendulum hit the second one in
phase, the oscillation amplitude of the secon
increase evidently.
y
x
Figure 4 Seoi-nage phase II
The motion of U is a complex movement
roto-traslazional which would require a full
description of its analysis on three planes zy
(side view of the action, which is the choice for
shooting with the camera used in the movie), zx
(frontal view over to the initial direction of
motion of the two athletes), xy (view from the
action). We observe that only in phase II is
involved in a significant interaction between the
mat and the foot of U and only in phase IV, the
motion is predominantly determined by the weight
force acts on U. Overall, the rotational movement
of the body of U occurs upon interaction with T.
z
U T
Conclusions The context of sport offers many
opportunities to evidence how physics can
construct models analyzing complex and not
controlled phenomena. A proposal for physics in
the context of judo was designed, starting from a
video-analysis of throwing actions and modeling
of the motion using a rigid body model. The
outlined path starts from the description of the
trajectory of significant points of Uke's body
and it provides a description of movement in
space. This enables us to see what actually
happens in the process and to selecting the
interesting aspects, in particular allowing to
identify the critical points of the motion
(related to the instants of discontinuity in
external conditions for U) (RQ1). He presented
modality can be used in all school provided by
computers, because use the standard tools for
picture elaboration. Can be also simply
implemented using commercial didactic tools
usable for image analysis (RQ3). The analysis of
a throwing technique is performed in three steps
video-analysis of the trajectory of two points
(the shoulder and the hip) of the body of Uke
kinematical analysis and description of the
motion of the selected points (RQ1) construction
of simple rigid body models that explain the
observed motion to extract information of the
couple of forces acting on Uke and applied by
Tori. The action of the couple of forces is
proposed analyzing in detail the seoi-nage
techniques (RQ2). The efficient transfer of
energy, momentum and angular momentum in the judo
throwing action is also considered. It is
particularly evident in the case of
okuri-ashi-barai technique. It give the
opportunity to show with a simulation, realized
with a commercial simulation software (RQ3) of
two pendulum how it is possible realize an
efficient coupling between two physical system
(RQ2).  The future goal of the research is to
construct an educational path, based on the line
here described, and the related didactic
instruments, experiment and validate the proposal
in pilot classes and monitor the learning path of
students. All materials will be offered on the
web for physics and physics education teachers.
Fig.10 Simulation of the resonant coupòling of
two pendulums.
y
x
Figure 4 Seoi-nage phase III
Since our goal is not to account for all the
details of the phenomenon, but just to
characterize the interaction between the
athletes, we can choose to restrict the analysis
to only motion on the zy plane on which lie
mainly in directions d 'action of the forces of
interaction between T and U only in the phases
II, III, IV.
z
U T
y
x
Figure 4 Seoi-nage phase IV
The trajectory points of the body. What kinds of
trajectory describe the individual parts of the
body of U in the plane zy chosen for analysis? To
answer this question, we can restrict the
detailed analysis of just two points on the body
of U the right shoulder, right hip, which allow
describing in good detail the motion of the trunk
of U. They were selected from among the points
which recognizes significant biomechanics to
describe the different parts of the body
(Sacripanti 1996 Blaise 2001) The analysis of
the motion of the shoulder and hip motion, allow
to point out that the trajectory followed by
different parts of the body of U is a kind of
spiral as shown in the fig. 5.
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Figure 5 Seoi-nage The trajectory of the
shoulder
Figure 5 Seoi-nage The trajectory of
the hip
From the analysis of the variation in the
direction of the displacement vector can be
deduced the evolution of the instantaneous
angular velocity. It is on average increased
approximately linearly (see graph), as might be
expected in a spiral motion with near-uniform
velocity, from 0 rad s-1 to 10 rad s-1 in 0.7 s,
an angular acceleration average of 14 rad s-2
(you can make a rough estimate considering that
the body of U rotates to 3 / 2 ? in 0.7 s with
an average speed of about 6.7 m s-1 which is in
good agreement with the average value of 6.8 m
s-1della angular velocity measured by the video).
from 0.00 s to 0.68 s from 0.68 s to 1.08 s
ltVygt 2 m/s ltaygt 1,3 m/s2 ltVygt 0.93 m/s ltaygt -5.9 m/s2
ltVzgt 0 m/s ltazgt 0 m/s2 ltVzgt -1.95 m/s ltazgt -5.8 m/s2
The similar analysis of motion of right hip U
leads to a recognition essentially two trends
0.0 - 0.68 s (range corrensponding to the phases
I, II and III) and 0.68 -8.1 s (range
corresponding to the phase IV), characterized by
the data shown in the table.