Physics competitions PREFACE

We have to apologize that this fourth physics competitions section (for 2011) comes after some delay, with the 2012 competitions having already been performed in the meantime.This section contains three papers. Before addressing their content, we would like to indicate the locations of the events. The 42nd International Physics Olympiad took place in Bangkok, Thailand; the 24th International Young Physicists' Tournament was organized in Tehran, Iran; and the 'First Step to Nobel Prize in Physics' competition was conceived in Poland. This not only shows the true internationality of these events, but also indicates that political situations and influences are and should be in the background. This is even more important since these events are organized for and carried out by young students, the next generation of scientists, for our future.The organizers of the 42nd Physics Olympiad present three theoretical and two experimental problems, all of them with solutions. The theoretical topics range from the Laser Interferometry Antenna (LISA) through an electrified soap bubble to a commemoration of Rutherford's discovery of the atomic nucleus. The experimental tasks are interesting since both were set on black boxes, one mechanically and one electrically driven. Finally, the scores of the students are displayed and discussed. It may be surprising that the students with high scores in the experimental part almost all exhibited high scores in the theoretical tasks, whereas the reverse did not hold.The other two papers have in common that they approach their tasks through both experimental and theoretical means. In the first the possible deformation of a meteor into a lens shape when entering the atmosphere is exemplified by molten tin falling into water and by wind tunnel experiments, accompanied by a theoretical model. The second problem deals with a cup drum, a musical instrument that changes the frequency of its sound depending on whether the cup is held over, close to or under water. Frequencies and amplitudes are measured for all cases and theoretical explanations given, partly quantitatively, partly only qualitatively