# Solution approaches

As I have already said, IYPT reports cannot be made in only one afternoon. The approach to the final solution sometimes goes very slowly, and sometimes you might also be misguided and follow a completely wrong path. I want to give examples how we have approached solutions during our preparations work. You have already read some of our final reports, but now you will see, how these reports were written and constantly changed until the very last minute.

## Problem no. 3 "Magic motor"

When we started to work on this problem, first we were very confused. As we believed to know a DC motor cannot work without a commutator. We thought this problem might be some kind of bad joke. Perhaps one should prove that it is not possible to construct such a motor. So we did an experiment and we were really amazed when we saw the motor working for the first time. It was actually working!
We only had to find a scientific explanation for the phenomenon.
Our first attempt was very primitive. We thought: If something is rotating there has to be a force which causes a torque which causes the rotation. We have a magnetic field and a current in our experiment, so there must be a Lorentz force acting. So we made hand-painted sketches (which we later improved into the diagrams of the acting Lorentz forces.
With these diagrams we found out that there is an acceleration and a braking phase. Furthermore we found out, that on the first look the accelerating forces and the braking forces were equal. Due to the fact that nevertheless the motor worked, we had to find some reason why the forces were not equal. We thought of two main explanations:

• Asymmetry: One side might be farther away from the axis of rotation. So on that side there would be a higher torque. This would cause the motor to accelerate more than it brakes. There is only one argument against this theory: In this case the motor could run only in one direction. However we observed the motor was running in both directions...
• Number of wires: If the coil has no wire through the axis there is always one wire more on one side of the coil. That would cause a higher torque on that side. This effect would force the motor in one direction only.

Being aware of the fact that these explanations were insufficient we prepared a report for the AYPT containing only the information shown above. In the AYPT we challenged the team from the Lycee francais for that problem. Their report contained the theory with the regular interruptions. At that time we did not believe this explanation. So there was quite a "hot" discussion between the reporter and myself. As I can remember the jury gave both, the reporter and the opponent a very good grading for the brave and interesting discussion.
However when the fight was over we thought more about the theory of interruptions and after some experiments we had to admit that our solution was incomplete which does not mean that it is false. Of course there is an effect coming from asymmetry and from the different number of wires. But these effects are only side effects which support the main effect.
When solving an IYPT problem, you sometimes have to reconsider your whole solution. You have to see the things from a completely different point of view.