THEMATIC RESEARCH Ⅱ
Annual Report on Research Activities
Abstracts in English

2020
Kyoto Prefectural Rakuhoku High School

Contents
Chemistry
The Observation of the Differences in the Way Soap Bubbles Burst Depending on the
Component of the Soap Liquid .................................................................................................1
Yuko Tonami, Mina Ueno
Preventing Bacteria from Breeding Varied Substances ............................................................2
Akira Sawamoto, Manaho Ogiso
Keeping Your Hair Beautiful....................................................................................................3
Kanako Fujikawa, Fumika Sawasaka, Nanoha Yasuda
Why does graphite migrate to paper? .......................................................................................4
Kyoka Maeda, Syoko Mashimo, Rina Takashima
The Attempt to Make Adhesive by Using Polyvinyl Acetate .....................................................5
Shojiro Hori, Takuya Kira, Ryoichiro Oda

Biology
Do zebrafish have likes and dislikes? ........................................................................................6
Sogo Otsu, Ai Ozaki, Kaya Utsughi
The effect on the Learning Ability of Zebrafish Brought by Environmental Change ................7
Tatsuki Hattori, Taiga Miyaoku, Shintaro Takegama, Hirai Yagi
Breeding Fish and Ornamental Plants in a Balanced-Aquarium ..............................................8
Ayano Ogata，Yukiha Furuta
The Capability of Concept Cognition of Zebrafish ...................................................................9
Seiichi Honma, Masaki Sohno, Yuto Tanaka
Memory Experiment Using Planarians ...................................................................................10
Mizuki Fukui, Satomi Ikari, Saki Naganishi, Moe Yoshida
The Succulent Plants’ Callus Culture and Redifferentiation...................................................11
Tomoha Kojima, Fumika Ogawa, Megumi Tanaka
Can fish distinguish human faces? ..........................................................................................12
Risa Kinoshita, Noe Kimura, Aoi Sakurai, Tomoe Takabayashi

Environment
The Effect of the Mask in Communication .............................................................................13
Tensho Funakoshi, Tomaya Kimura, Yuma Kurashima, Takuto Oshima
How to Use Your Own Voice by Questionnaire and Frequency Analysis ................................14
Shiori Nishimoto, Kanako Zushi

Influence of Picture Books on Children Showed from Rakuhoku High School Students .........15
Takahashi Nahoka, Mitsushima Mei
Plastic = evil? .........................................................................................................................16
Erika Kubo, Manami Tsukada
What makes agar hard? .........................................................................................................17
Chiori Nakajima, Nodoka Shimo, Ryoko Matsumoto
Economical Structure of Building...........................................................................................18
Shiryu Seki, Rintaro Takahata, Haruki Maru, Ryohei Yamasaki
What Hobby Makes You Happy? ...........................................................................................19
Azusa Nakamura, Rena Hojo
The Relationship Between Colors and Appetite ......................................................................20
Yuki Hasegawa, Shiori Nishimoto
Do you know about agricultural technology?..........................................................................21
Shimada Hazuki, Nishiyama Kaho, Hamao Tomoha

Physics
The Effect of Spill Holes and Their Layouts on the Way a Parachute Falls ............................22
Nami Adachi, Kenta Iida, Chinatsu Natori
The Strength of “Tsugite” ......................................................................................................23
Ruka Nishida, Takumi Sumiya, Konatsu Teraoka, Shohei Yukawa
Water-Cooling Device Applied to the Hot Side of a Thermoelectric Cooler ............................24
Nene Akahori, Fuga Itagaki, Arata Fujimoto, Madoka Yamazaki

Mathematics
How to Measure the Distance Between Two Points on the Earth ............................................25
Tomoya Otake
The Power Law of Fall Impact with Jelly ...............................................................................26
Kento Igarashi
Setting Difficulties of Sudoku Problems by Using T-Algorithm ..............................................27
Hinata Tokuda, Hikaru Kojima

The Observation of the Differences in the
Way Soap Bubbles Burst Depending on
the Component of the Soap Liquid
Yuko Tonami, Mina Ueno

Abstract
We wondered what PVA’s role was in keeping a soap bubble’s shape. To figure this out, we focusedon the appearance of the black spot. The black spot appears on the soap bubble when the soap
membrane becomes very thin, so we thought that we can learn the change of the membrane’s thickness
by observing it. In the experiment, we gradually changed the proportion of the starch (its main
component is PVA) in the soap liquid and made a hemisphere bubble. Our research showed that, whena small amount of starch is added, the time until the black spot appears and the bubble bursts bothdecreased as the amount of starch increased. However, when we increased the amount of starch tosome extent, the soap bubble suddenly began to last for a long time. Also, when we increased theamount of PVA, the size of the black spot right before bubble bursting became bigger. In conclusion,
we thought that starch (PVA) would be helpful for us in maintaining the soap membrane in a thin state
and wide range, but it would quicken the time until the bubble breaks until we add a certain amountof it, maybe because it is easily affected by gravity.
Keywords: soap bubble, PVA, black spot1

Preventing Bacteria from Breeding
Varied Substances
Akira Sawamoto, Manaho Ogiso

Abstract
Due to the outbreak of the new coronavirus at the end of March 2020, rubbing alcohol was difficult
to obtain. Alcohol is an industrial product used for various purposes, and it may become difficult toobtain again someday. In this research, we looked for something familiar and inexpensive that can
prevent bacteria from breeding instead of rubbing alcohol. Then, we examined E.coli by counting
colonies. First, we examined the antibacterial effect of foods that are known to have an antibacterial
effect. We found that lemon and umeboshi have a great antibacterial effect, possibly because they
contain citric acid, which has an antibacterial effect. Next we did an experiment with oranges andlemons, which contain citric acid, and 30 g/ml acid solution in order to examine citric acid’s
antibacterial effect. Then, we unified the amount of citric acid to 9mg contained in the sample. This
research showed citric acid solution had the greatest antibacterial effect among what we examined. In
addition, it was found that the citric acid solution had a greater antibacterial effect than the sameamount of rubbing alcohol. Therefore, it seems that a 30g/ml citric acid solution can be expected as a
substitute for rubbing alcohol.
Keywords: bacteria, rubbing alcohol, citric acid, antibacterial effect2

Keeping Your Hair Beautiful
Kanako Fujikawa, Fumika Sawasaka, Nanoha Yasuda

Abstract
We checked on the relation between how long we add heat to the hair and what temperature the hairhas, and tried to find out the resistance the hair has. Also, we examined the change in resistance of hair
when we get a hair treatment or add a hair repairing material to the hair. We added heat to the hair withthe hair iron, pulled it by the weight of water, and cut it. In another experiment, we got hair treatments
before we added heat to the hair, and then we did the above-mentioned experiment. Our results showedthat the higher temperature the hair has and the longer we add heat to the hair, the lighter the weightof water is. Also, when we got a hair treatment or a hair repairing material to the hair, the weight ofwater was heavy. We considered that when we use the hair iron in order to set our hair, we should use
it for a short time and at low temperature as long as we can.
Keywords: resistance of hair, hair iron, heat3

Why does graphite migrate to paper?
～To protect handwritten drawings～
Kyoka Maeda, Syoko Mashimo, Rina Takashima

Abstract
We sometimes have a problem when graphite migrates to paper. To prevent it we want to understandwhy it happens and find the way to avoid it. We made a hypothesis that it was easier for graphite tomigrate when we write with dark pencils. We examined especially 2B, B, HB, F, H. We used black
pencils made by Mitsubishi Uni, tracing paper, and black paper on which we wrote something such as
straight lines or circles filled by graphite. Second, we piled them up, put them between boards, put anaquarium on them, and left them for one week. Finally, when one week passed, we observed how thegraphite migrated to the paper through observing with a binocular microscope or checking the masschange of each piece of paper. We made the following. Although darker pencils are easier for graphite
to migrate to paper, for 6B and 3B, it is easier for 3B to migrate. Regarding 2B~H, no clear change inmass was observed, so we couldn’t find the darkness which is hardest for graphite to migrate.
Keywords: graphite, migration, darkness

4The Attempt to Make Adhesive by Using
Polyvinyl Acetate
Shojiro Hori, Takuya Kira, Ryoichiro Oda

Abstract
Adhesive generally contains water and polyvinyl acetate. We think changing the proportion of themaffects the strength of glue. We constructed the hypothesis that the more polyvinyl acetate we use, thestronger we can make an adhesive. In order to make an adhesive, first, we made vinyl acetate into
polyvinyl acetate by connecting it, and made polyvinyl acetate partly dissolve in water. However, wefailed our experiments three times, so we could not make an adhesive. From these results, we found it
difficult to make an adhesive by ourselves.
Keywords: adhesive, proportion, failure5

Do zebrafish have likes and dislikes?
Sogo Otsu, Ai Ozaki, Kaya Utsughi

Abstract
We researched whether zebrafish have likes and dislikes by feeding them three types of food.
Conditioning them to see colored papers corresponding to each food, we sought to confirm thequestion by their reaction to the paper. Moreover, by using colored papers instead of electric current,
our experiment was more humane for the fish. Our results show that may have likes and dislikes.
According to the experiment results, they liked Artemia the best, Tetra Min second and Red Wormthird. We concluded that they obviously have likes and dislikes, but colored papers would not be analternative method of electric current. We suspect that better-liked foods are connected to the amountof protein.
Keywords：zebrafish, colored papers, foods (Artemia, Tetra Min, Red Worm ), likes and dislikes

6The effect on the Learning Ability of
Zebrafish Brought by Environmental
ChangeTatsuki Hattori, Taiga Miyaoku, Shintaro Takegama, Hirai Yagi
Abstract
We knew about research which shows the danger that fish may behave abnormally due to marine
acidification. The reason why we guess they do is that they have to use more energy than necessary inorder to avoid a harsh environment and we started a study to confirm our hypothesis by using zebrafish
which live in fresh water. However, it is difficult to maintain acidity in the aquarium, so we chose away to compare between normal keeping and 0.5% salinity keeping. Our study is a learning
experiment where we compared the reaction between when we showed red on a screen, which meant
we would give food, and when we showed blue, which meant we would give a shock: we did thistwice a day. As a result, we could observe that the physiological cost made them difficult to study.

Keywords: zebrafish, marine acidification, physiology

7Breeding Fish and Ornamental Plants in
a Balanced-Aquarium
Ayano Ogata，Yukiha Furuta

Abstract
Preparing the environment of the aquarium needs a lot of electricity, and it has bad effects on earthsuch as global warming. Therefore, we examined the necessary condition of reducing those risks andbreeding fish more easily. In our research, we prepared two types of PET bottles of different sizes forthe tank, and put one fish, one ornamental plant into such of them. By using this equipment, we
experimented which size of PET bottles can make more numbers of fish survive than another. The pH
and DOD figures were checked with exclusive equipment, and we checked visually on the water
quality. At that experiment, fishes were not fed for three weeks out of four weeks. As a result, all fishes
in 500mL PET bottles died, and 3 out of 4 fishes in 1500 PET bottles survived. There was no variationof pH and DOD figures, but water quality of 500mL PET bottles got much worse than 1500mL PET
bottles in appearance. From these results, we considered that the size of bottle does not affect thevolume of respiration, therefore pH and DOD figures did not vary, but that closely related to water
quality. We estimated that because of deterioration of water quality, fishes in 500mL PET bottles died.
Based on these considerations, we concluded that 500mL PET bottles are not fit to breed fish.
Keyword: pH，DOD

8

The Capability of Concept Cognition of
Zebrafish～Experiment on Shape Cognition～
Seiichi Honma, Masaki Sohno, Yuto Tanaka

Abstract
We humans grasp things we see by connecting them with the information of other similar facts wehave learned in the past. This is concept cognition, and it is said that only humans have this ability.
However, we thought fish also has this ability because they can tell their companion from their natural
enemy immediately. In our research, we made zebrafish memorize two different shapes by feedingthem or giving electric shock when showing a particular shape, and observed how they moved when
randomly shown either of the shapes. Our results showed they didn’t show specific reaction in any
case. From the results, we concluded they couldn’t identify the shapes we used in the first place, andwe couldn’t get any valuable information about their ability of concept cognition.
Keywords: concept, cognition, shapes

9Memory Experiment Using Planarians
Mizuki Fukui, Satomi Ikari, Saki Naganishi, Moe Yoshida
Abstract
Planarians are a kind of leech. They avoid light, and can remember. We researched whether theywould approach food when they were hungry, and if they knew their food was in the lighted place,whether they would move toward the place. In our research, we divided them into two groups, one isfull, and the other is hungry. Then, we compared the speed of them going to the light. Our results
showed that the hungry group moved toward the light faster than the other group. However, in bothgroups about half of them didn’t move, or moved opposite to the light. These results indicate two
possibilities. One is that the frequency of feeding is too high, so some of them didn’t move. The otheris that they dislike light so much that even if they could get some food, they will not move.

Keywords; planarians, lighted place, speed

10The Succulent Plants’ Callus Culture andRedifferentiation
Tomoha Kojima, Fumika Ogawa, Megumi Tanaka

Abstract
Callus is a plant cell mass that is amorphous and can differentiate into various tissues. When theleaves of succulent plants, whose leaves and stems contain a lot of water fall, callus is formed on theircut ends. We thought that the speed of the formation of callus and the look of the redifferentiationdiffered depending on the quantity of nutrients and hormones contained in the leaves. We used four
succulent plants of two kinds and cut the apical buds from two plants, and recorded how long it would
take until the callus redifferentiation. We also cultured part of the leaves in culture mediums and tried
to make callus. Our result showed that the speed of the callus redifferentiation differed from variety
to variety but was not affected by the position and weight of leaves and whether the plant had had theapical bud or not. The culture ended in failure and we could not make callus in culture mediums. Fromthese results, we conclude that we have to change the concentration of the hormones and circumstances
widely and accurately to affect the callus formation and redifferentiation.
Keywords: callus, redifferentiation, hormone, succulent plant

11

Can fish distinguish human faces?
Risa Kinoshita, Noe Kimura, Aoi Sakurai, Tomoe Takabayashi

Abstract
Some mammals, birds, and even insects can distinguish human faces. We learned that archerfish,
which prey on insects by shooting water from their mouth, can distinguish human faces, so we
conducted experiments to find out whether zebrafish can also do this. In our research, we trained
zebrafish to recognize two faces by using feed as a reward and an electric current as a penalty. Then
we tested whether they could distinguish those faces. Our result showed they gathered more at the facethat we showed to them while applying an electric current, or they gathered at neither of the faces.
From these results, we concluded that zebrafish cannot distinguish human faces. We assume that thisis because zebrafish don’t need to prey on insects, so they don’t have the ability to watch things
carefully, unlike archerfish.
Keywords: zebrafish, distinguish, recognize, human faces

12The Effect of the Mask in
Communication
Tensho Funakoshi, Tomaya Kimura, Yuma Kurashima, Takuto Oshima

Abstract
We must wear a mask because of the pandemic, so we tried to find a better communication methodfrom mask’s comments. In our research, we prepared a listening test in order to research the effect ofmasks on voices and communication. Next, we prepared a questionnaire about the impression of clear
masks. As a result, there was no significant difference in dB, Hz. Also, it is more important to movethe mouth than the area around the eyes. It also revealed that students want to wear normal masks andwant our teachers to wear clear ones, from our questionnaire.
Keywords: mask, effect, communication

13

How to Use Your Own Voice by
Questionnaire and Frequency Analysis
Shiori Nishimoto, Kanako Zushi

Abstract
We want you to know the advantage of your own voice and to communicate smoothly, so we started
to examine what kind of voice people like depending on each situation or gender. We sent twoquestionnaires to 228 students, and the participants listened to the voices we prepared. We analyzed
them into frequencies. Our results from the questionnaires showed that the voices people like aredifferent from situation to situation or gender. We also found what those voices have in common, suchthings as pitch, speed, clarity, and age. From these results, we conclude that the likable voices varyfrom situation to situation or gender, so we can safely say that each person has the chance that they
can use their own voice efficiently.
Keywords: voice, pitch, speed, clarity, age

14Influence of Picture Books on Children
Showed from Rakuhoku High SchoolStudents
Takahashi Nahoka, Mitsushima Mei

Abstract
We carried out our research to find the effect of picture books on children and to see if they havesome effect even on high school students. In our research, we sent a survey on what Rakuhoku students
learned from picture books, when they read them, how much they were affected by them, and how
they got the books. In addition to this survey, we sent another survey on Instagram to find how much
picture books affected older people when they were high school students. Our results showed few links
among the categories we searched. From these results, we conclude that high school students are
significantly affected by picture books, but that they will be affected by many other things throughtheir growth, so we could not find a clear connection.
Keywords: picture books, high school students

15

Plastic = evil?
Erika Kubo, Manami Tsukada

Abstract
These days the issue of plastic waste is being talked about. However, due to the influence of
COVID-19, many shops and restaurants have started takeout. We thought this would cause more
plastic waste. In our research, we interviewed two companies, MARUGAMEUDON and McDonald’s,
about the materials they use for the containers, their opinions on the environment and the problems
they face when they enforce environmental protection. Both of them work on environmental protection.
Second, we asked Kameoka city. They are trying different initiatives such as a coupon campaign andthe introduction of paper containers. Therefore, it is thought that the most important thing for us is to
be interested in environmental issues and to act in cooperation with companies and local governments.
We want to think about how to utilize it in the future.
Keywords: plastic, environment

16

What makes agar hard?
Chiori Nakajima, Nodoka Shimo, Ryoko Matsumoto

Abstract
We studied what makes agar hard, particularly Mg²⁺ and Ca²⁺. From a study last year, it wasconsidered that high hardness water makes agar hard. However, all the results were surveyed byquestionnaire. We tried to prove what makes agar hard, focusing on Mg²⁺ and Ca²⁺, because water
hardness is measured by the level of salt, such as Mg²⁺ and Ca²⁺, in water. We made 10 agar gels with
5 types of water in 10 test tubes and measured their melting points. In our research, agar which has ahigh melting point is considered hard. Our results showed that agar with distilled water always melted
first. Thus, we can conclude that the more impurities water contains, the harder agar becomes.
Therefore, we can say that the consideration of the study last year was true.
Keywords: agar, hardness, Mg²⁺, Ca²⁺, melting point

17Economical Structure of Building
Shiryu Seki, Rintaro Takahata, Haruki Maru, Ryohei Yamasaki

Abstract
These days, the international pandemic of Corona virus occurs all over the world. Therefore, people
pay attention to ventilation, which is regarded as a precaution to protect people from spreading theinfection. We suspected that changing the shape of a room leads to effective ventilation and we did anexperiment based on the idea.
In our research, we prepared four differently shaped solid models, made out of plastic. We produced
smoke by using a smoke machine and blew air towards the models. Our result showed that air in theregular icosahedron was circulating most efficiently of the four shapes. For this reason, we expectedthat the closer to a sphere shape the model was, the more efficiently the air in the solid model circulated.
For further research, we have to examine what types of shapes are most useful for our lives.
Keywords: corona virus ,circulation, solids

18What Hobby Makes You Happy?
~The Relationship Between Hobbies andSubjective Happiness, and the Change in
Hobbies by COVID-19 Pandemic~
Azusa Nakamura, Rena Hojo

Abstract
The purposes of this study are to clarify the relationship between hobbies and subjective happiness,and to propose a new lifestyle which people can keep themselves happy even when they cannot live
as they want because of COVID-19 pandemic. We conducted a questionnaire survey on Rakuhoku
High School and Junior High School students and analyzed the data. As a result, we found that hobbies
were deeply related to subjective happiness and could guess they maintained their happiness byincreasing the time to enjoy their hobbies during the self-restraint period.
Keywords: hobby, subjective happiness, COVID-19, self-restraint period

19

The Relationship Between Colors andAppetite
Yuki Hasegawa, Shiori Nishimoto

Abstract
Generally speaking, it is said that warm colors promote appetite, and that cool ones reduce appetite.
We researched whether it is true, and would like to suggest how to take pictures in order to promote
more appetite. We investigated through a questionnaire survey in what cases appetite would increase.
As a result, when the color of each dish was processed, many people felt that green and yellow looked
delicious. Therefore, it is concluded that people can be motivated by changing the background colorsof advertisements made for the general public to so-called “natural colors”.
Keywords: appetite, warm colors, cold colors

20

Do you know about agricultural
technology?
Shimada Hazuki, Nishiyama Kaho, Hamao Tomoha
Abstract
Farming in Japan has the serious problem of an aging population. We found that agricultural
technology is a solution to the problem, but it has not spread yet in Japan. Thus, we want to find out
why it has not become common and have started this research. We expected that the main obstacles
would be the cost of its introduction and the difficulty in using it. Furthermore, to make it widespreadin Japan, farmers would need financial support. From these results, we conclude that the reason why
agricultural technology is not widely used is that Japanese farmers have financial constraints.
Therefore, we think what farmers want is smaller and cheaper machinery. Our results showed 64％
of farmers expected to adopt agricultural technology. Staffs of agricultural technology companies were
sure that farmers would make a profit.
Keywords: agricultural technology, farmers, financial support

21

The Effect of Spill Holes and Their
Layouts on the Way a Parachute Falls
Nami Adachi, Kenta Iida, Chinatsu Natori

Abstract
We learned that some parachutes have holes on their canopy. They are called “spill holes” and they
help parachutes fall more stably. We decided to research the effect that the number and layout of holes
have on a parachute’s fall. We constructed the hypothesis that the more holes a parachute has, the morestably it will fall. In our research, we made 6 models of parachutes using polyethylene plastic bags,
each with a different number of holes. We dropped these models and observed and compared eachmodel’s trajectory and speed. Our results showed that the parachute with 4 holes swung the least, andthat the speed of parachutes was relatively consistent regardless of the number of holes. From theseresults, we conclude that parachute trajectories change depending on the number of holes, but thatwhen the size per hole becomes bigger than is appropriate, there seems to be no difference in theirtrajectories.
Keywords: parachute, spill holes, trajectory

22

The Strength of “Tsugite”～ The ancient building techniques ofJapan～
Ruka Nishida, Takumi Sumiya, Konatsu Teraoka, Shohei Yukawa

Abstract“Tsugite” has been used to connect wood for a long time in Japan. We focused on it and conducted
an experiment to find what effects Tsugite structures have. In this experiment, we prepared woodconnected by Tsugite, and defined the “strength” of Tsugite as the weight it could endure when pressure
was pressed on joints. We used four types of “Kanawatsugi” in the experiment. We expected that thelarger the cross-sectional area was, the bigger the frictional force would be, and therefore the greater
the “strength” would be. However, from the results of the experiment, we found that there was no
relationship between the cross-sectional area and the “strength” of Tsugite. On the other hand, if thestructure was changed, the "strength" was also changed, even using the same type of Tsugite.
Keywords：Tsugite, Tsugite structures, four types of “Kanawatsugi”, the “strength”

23

Water-Cooling Device Applied to the Hot
Side of a Thermoelectric Cooler
Nene Akahori, Fuga Itagaki, Arata Fujimoto, Madoka Yamazaki

Abstract
Technologies have developed recently, and modern devices do much more processing, and easily
get hotter than before. In order to prevent them from overheating, a more efficient cooling system isneeded. We investigated a way to use water as a means of cooling them. In our research, we put Peltier
devices, which are one type of the thermoelectric devices in PCs, on a metal plate, and heated themetal in various situations. After heating, we recorded the temperature of the plate. Our results showed
that, by dripping water, we can cool the metal faster. Especially, when the temperature of the metal
plate was above 100 degrees Celsius, the metal was cooled in a much shorter time. From these results,
we conclude that using water’s vaporization enables us to absorb the heat efficiently. Water cooling isuseful when the temperature is high enough to evaporate water.
Keywords: water cooling, Peltier device, water vaporization

24

How to Measure the Distance Between
Two Points on the Earth
Tomoya Otake

Abstract
As we become more internationalized, we are expected to measure long distances accurately andeasily. I studied the accuracy of existing equations for finding the distance between two points(Spherical trigonometry, Huveni’s equation) with the aim of creating my own equation for finding
distances. I compared the calculation results of these formulas with the true values, and examined whysuch errors occur. As a result, I was not able to create my own equations, which was my first goal, but
I learned the following. The method using Spherical trigonometry is more complicated to calculate,but it is less prone to make errors even over long distances. The method using Huveni’s equation iseasy to calculate, but the error becomes extremely large when the range exceeds 1200 km from northto south and 3000 km from east to west. From the above, I was able to find some points for
improvement, which I would like to examine in the future.
Keywords: Spherical trigonometry, Huveni’s equation, measuring long distances

25

The Power Law of Fall Impact with Jelly
Kento Igarashi
Abstract
There are many natural phenomena which act based on the power law. This law is expressed in theformula, “y=bxa”. When you take the common logarithm of both sides, it changes to the straight lineof slope a, intercept b. I thought that the distance of each range regularly from the fall point and thetotal mass of the broken piece scattered on each range might follow this law. In my research, I madeagar jelly and dropped it from the second floor of my school. After each drop, I caught a piece of jelly
with a spoon and measure its mass. My research showed that the value of the range away from the fallpoint approximated to the straight line, but that the closer to the fall point broken pieces landed, thelarger the gaps became. Also, the spread of the data of the same range was as big as I expected. Fromthese results, I conclude that it is easy for big pieces of broken jelly to stay less than 25cm from thefall point, while small pieces are likely to scatter, following the power law.
Keywords: power law, common logarithm, agar jelly

26Setting Difficulties of Sudoku Problems
by Using T-Algorithm
Hinata Tokuda, Hikaru Kojima

Abstract
These days, “Sudoku” or “Number place” is very popular all over the world. However, there wasno sufficient measure to evaluate Sudoku’s difficulties. Therefore, we defined the new one named “Pscore”, which is calculated by using an algorithm to count up all the solutions of a given Sudoku grid.
We made such an algorithm and calculated the P-score of around 700 problems, and checked how
accurate it is. Our results showed that there was a certain relation between P-score and Sudoku-entropy,
another indicator of Sudoku’s difficulty proposed by Zhe Chen. The correlation coefficient was 0.826.
We also found a relation between P-score and the claimed difficulty of DAISO Sudoku. On the other
hand, there was no relation between P-score and the claimed difficulty of Byakuya-shobo’s Sudoku.
We suspected that this was the result of the tendency for P-score to be widely affected by the numberof empty cells. We conclude that P-score’s accuracy is not high because it does not reflect how aperson solve the problem. Still, since no effective way to evaluate the difficulties of Sudoku problems
is found yet, we believe that P-score is a useful method to set a difficulty.

Keywords: Sudoku, number place, difficulty, algorithm27