# The 12th IYPT

Vienna (Austria), May 23rd - 29th, 1999
Homepage of the 12th IYPT

## The Problems of the 12th IYPT

These are the problems formulated by the IOC (International Organising Committee) for the 12th IYPT:

1. Rotation

A long rod, partially and vertically immersed in a liquid, rotates about its axis. For some liquids this causes an upward motion of the liquid on the rod and for others, a downward motion. Explain this phenomenon and determine the essential parameters on which it depends.

2. Ionic motor

An electrolyte (an aqueous solution of CuSO4, NaCl, ...) in a shallow tray is made to rotate in the field of a permanent magnet (a small "pill" placed under the tray). An electric field is applied from 1.5 V battery in such way that one electrode is in the form of a conducting ring immersed in the electrolyte - the other is a tip of a wire placed vertically in the centre of the ring. Study the phenomenon and find possible relationships between the variables.

3. Magic motor

Construct a DC motor without a commutator, using a battery, a permanent magnet and a coil. explain how it functions.

4. Soap film

Explain the appearance and the development of colours in a soap film, arranged in different geometrical ways.

5. Dropped paper

If a rectangular piece of paper is dropped from a height of a couple of meters, it will rotate around its long axis whilst sliding down at s certain angle. What parameters does the angle depend on?

6. Singing glass

When rubbing the rim of a glass containing a liquid a note can be heard. The same happens if the glass is immersed in a liquid. How does the pitch of the note vary depending on different parameters.

7. Heated needle

A needle is hanging on a thin wire. When approached by a magnet, the needle will be attracted. When heated, the needle will return to its original position. After a while the needle is attracted again. Investigate this phenomenon, describe the characteristics and determine the relevant parameters.

8. Energy converter

A body of mass 1 kg falls from a height of 1 m. Convert as much as possible of the released potential energy into electrical energy and use that to charge a capacitor of 100 µF.

9. Air Dryer

During a time span of 4 minutes collect as much water as possible from the air in the room. The mass of the equipment must not exceed 1 kg. Its initial temperature should be equal to room temperature. The water should be collected in a glass test tube, provided by the jury.

10. Charged balloon

An air filled balloon rubbed with wool or dry paper may stick to the ceiling and stay there. Investigate this phenomenon and measure the charge distribution on the surface of the balloon.

11. Billiard

Before a pool-billiard game starts, 15 balls form a equilateral triangle on the table. Under what conditions will the impact of the white ball (16th ball) produce the largest disorder of the balls?

12. Flour craters

If you drop a small object in flour, the impact will produce a surface structure which looks a like moon crater. What information about the object can be deduced from the crater?

13. Gas flow

Measure the speed distribution of the gas flow in and around the flame of a candle. What conclusions can be drawn from the measurements?

14. Wheat Waves

The wind blowing through a wheat field creates waves. Describe the mechanism of the wave formation and discuss the parameters which determine the wavelength.

15. Bright Spots.

Bright spots can be seen on dew drops if you look at them in different angles. Discuss this phenomenon in terms of the number of spots, their location and angle of observation.

16. Liquid diode

Make an electrochemical diode and investigate its properties, in particular the frequency dependence.

17. Sound from water

When you heat water in a kettle you hear a sound from the kettle before the water starts to boil. Investigate and explain this phenomenon.

## General comments on the problems

From my point of view most of the problems for the 12th IYPT can be divided into three main groups:

1. Problems concerning effects and phenomena which we all know from our everyday lives and things, which many of us have already observed or thought of. For example problem no. 6 "Singing glass": I think everyone has already tried to produce sounds with a partially filled glass, and to compare this sound to differently filled or shaped glasses. Another problem of this group is no. 10 "Charged balloon". Children are fascinated when they see how their balloons stick to the wall or the ceiling after having been rubbed with some wool. Moreover I am sure that many people have already seen what it looks like when the wind is blowing through a wheat field, or that bright spots can be seen in dew drops. Some people may also sometimes have noticed that there is a sound coming from a kettle before the water starts to boil. Although many people know these phenomena only very few people know why these phenomena happen or which parameters determine them. The fact that a problem concerns a well known phenomenon does not necessarily mean that this problem is easy to solve. Sometimes these problems are the most complicate ones.

2. Problems about easily imaginable phenomena, which are normally not a part of our everyday lives. That means for example no. 12 "Flour craters". Also non-scientists can imagine that differently shaped and sized objects leave different craters, when dropped into flour. But in contrast to problems from group 1 this isn't an effect which we may encounter in our daily routine, such as wheat waves or singing glasses. Other problems of that type are no. 13 "Gas flow", no. 11 "Billiard" and no. 4 "Soap film".

3. Problems for which you already need at least some "basic" science knowledge in order to imagine what they are about. More or less that's the rest of the problems, especially no. 1 "Rotation", no. 2 "Ionic motor", no. 3 "Magic motor", no. 8 "Energy converter", no. 16 "Liquid diode".

For some problems it is difficult to say in which group they fit in best.
I have divided the problems into groups, because for each type of problem there is a different way how to start working.

For problems of group 1 ("every-day-life-problems") it's often useful to start with a large number of experiments. In most cases it's not very difficult to perform experiments on such problems, because they need neither very much nor very expensive or complicate equipment. Moreover, there are a lot of obviously relevant parameters. Of course there can always be "hidden" relevant parameters, but normally you can easily imagine the most important ones. E.g.: Problem no. 6 "Singing glass". Without hesitating a physicist can easily imagine that for example the shape of the glass (diameter, height, thickness,...), the amount of liquid in it, the viscosity of the liquid, the density of the liquid, probably also the temperature of the glass and the liquid are relevant parameters. So during the experiments it would be wise to change the values of these parameters systematically and to find out how the result changes. That sounds quite easy, but it's not only a lot of work but also sometimes very tricky because some of the parameters can't be easily isolated. For example if you change the density of the liquid, which practically means you take another liquid, the viscosity may change as well. So you can't be sure whether noticeable changes in the results depend on the viscosity- or on the density change.

Another difficulty is that some parameters are not as variable as they may seem to be. For example you can't vary the radius of the glass as far as you may want to, because glasses with unusual dimensions (e.g.: 50 cm high, radius: 1 m) are not easily available.

After having done all your experiments you can compare your measurements with calculations, by using formulas from literature or "self-designed"-formulas you get by combining others. If the calculations and the measurements fit, your work is almost finished.
That is of course the ideal case which will probably never occur, because you can be sure that you encounter some kind of difficulties which cannot be solved by standard procedures. Otherwise it wouldn't be an IYPT-problem.

Problems of type 2 are often solved in a more theoretical way. That is because experiments would be more difficult to perform. That does not mean that there are no experiments to be done, but if you do some, you should do them in a different way than the one mentioned before. For example problem no. 11 "Billiard": Trying to perform experiments on this problem will confront you with 2 major problems. The one is, that you can't vary parameters accurately, because you can't do two identical experiments. With a problem such as singing glass you can do an experiment, try the experiment with the same parameters again the next day, and the results will be equal.
But you can't do 2 identical Billiard experiments. Even if you try hard to keep all parameters (shot angle, velocity,...) equal the results will be different. So it's quite problematic to produce statistics.
The second major problem is that you don't have an easily measurable result. With the "Singing glass"-experiment you have to measure the frequency of the sound, which is not very difficult, but how can you measure the disorder of billiard balls?
That's why these problems are more of a theoretical nature, although you should always do some experiments to compare them with your theoretical results.

The methods to solve problems of group 3 may vary depending on the problem. Some of them can be solved by experiments, some of them are of a more theoretical nature. Experiments on such problems may be complicated, because as they are more difficult to imagine the relevant parameters are often not so obvious. Sometimes you find them only by chance...

One thing however is always the same: You have to read the task very carefully! The International Organising Committee (IOC) really works hard and long on the formulation of the problems. And that is very important, because the way a problem is formulated influences very much the way the problem is going to be solved. Single words may change a lot. E.g.: The task of problem no. 6 "Singing glass" says: "...glass containing some liquid.". It is very important that it says "liquid" and not "water"! If it said "water" the problem would be much easier because some of the relevant parameters would become constant (density of the liquid, viscosity of the liquid, surface tension,...). If you don't read the text carefully enough, you may forget to try to vary these parameters too. If your opponent finds that out, your grading will be effected negatively.
I remember many cases when teams were discussing the meaning of task formulations because one team was of the opinion that the other team had not solved the task as it was formulated. Misunderstanding the task may have a large impact on the grading. So before you start your work you should read the text meticulously.

All these comments are not supposed to explain any kind of standard procedure in order to solve IYPT problems, because such procedures do not exist. The division of the problems is subjective too. Some problems are a mixture of the types I have mentioned. Furthermore other persons may find a different division, depending on their personal experiences.
I just wanted to give some hints what a solution approach may look like and to point out possible difficulties and mistakes.

Moreover I would like to mention my 3 favourite problems: no. 14 "Wheat Waves", no. 13 "Gas Flow" and no. 3 "Magic motor" (in that order).

## Chronology of the preparations work

It was in October 1998 when we first heard about the IYPT. Strictly speaking we heard about the AYPT (Austrian Young Physicists' Tournament). We did not know anything about this tournament. We only knew that in spring of 1999 there would be some kind of physics competition for a team of 5 students in Vienna and that the winning team would participate in an international competition about one month later. Since we were all more or less interested in physics we agreed on participating in the AYPT, absolutely not knowing what it would be about. Then, in November we got the list of the problems. Reading through the problems we were a bit confused, because we did not know what to do. So we decided to forget all that and to prepare for the Physics Olympics because this was something which we were familiar with. But at the end of February we heard that only 3 teams would participate in the AYPT. So our chances would not be so bad, even without any experience, and we decided to accept the challenge. Now the only thing which we knew was that the teams should prepare presentations of their solutions of the problems.
Because there was only about one month left until the AYPT and because we were not informed about the regulations of the tournament the preparations work was a bit disorganised. We performed a few experiments, thought a bit about the main physical aspects behind the problems and wrote (very) short summaries of them on overhead transparencies.
I personally had enough work with translating the technical terms in my presentations and (having been in the 6th class of an AHS then) with trying to understand what my teacher told me about the important physical concepts.
So looking back I have to admit that our preparations were rather poor even if we thought different that time.
On April 9th 1999, the day of the AYPT we were faced with reality. The other participating teams came from Vienna (Lycee francais de Vienne; GRGORG Wien 22, Polgarstraße) and from Mattersburg (Burgenland).
Some members of the team "Polgarstaße" had already participated in the 11th IYPT 1998 in Donaueschingen (Germany) so they had 2 major advantages:

• They already knew the regulations and their tasks in the competition.
• They knew much better how to prepare for the competition.

This was the first time we were told what this competition was like, how a physics fight was performed and what the team members actually had to do.
We tried to do our jobs as best as we could and to react spontaneously.
In the end the team from the Lycee francais won the AYPT, the team from Polgarstraße was on place 2 and we were on place 3.
The team from Mattersburg, which was on place 4, decided not to participate in any further activities concerning the IYPT. Due to the fact that Austria was hosting the international competition that year, it was able to send 2 teams. So the decision was made that the wining team and a team consisting of students from the 2nd and 3rd placed team would represent Austria in the IYPT 1999.
Moreover, it was decided that the two teams should prepare together and exchange all theories and all data, so that everyone could profit from everyone else's work.
So in the following month left we had meetings in Vienna and in Leoben. We tried to correct all the errors which we made in the AYPT. We emphasised more the preparation of a good presentation, improved our theories and measurements and also tried to prepare for the other jobs of the competition (Opponent, Reviewer).
Furthermore, we found out that the solutions we had for some problems were insufficient and we knew that opponents would not accept these as solutions.
We had learned that solving an IYPT problem was much more complicated than we thought before.
So there was quite a lot of work left and we could not manage to prepare sufficient solutions to all issues. Our new team-mates from Vienna, however, told us that other teams didn't have solutions to all problems either. Usually a well prepared team has 13 or 14 of 17 solutions. I am not sure, but I think we had 11 or 12 presentable solutions.

Since our preparations work for that IYPT was not very well planned and organised I will not go into further details and instantly present some examples of our reports.