200 Puzzling Physics Problems
Davıd L. Andrews · European Journal of Physics · 2001
The laudable idea behind this book and the nature of its content are clear from the title, and the authors have done a grand job in collecting together some truly challenging puzzles. The Problems themselves fill just under fifty pages; a short section of Hints follows, but it is the elaborately detailed Solutions that fill most of the book. A few of the more concise Problems are paraphrased on the cover, and give a flavour of the content, for example: `What would be the high jump record on the Moon?' `How long would it take to defrost an eight-tonne Siberian Mammoth?'. It is concisely expressed puzzles of the sort that I find the most interesting, often demanding extreme extrapolation from experience, coupled with the application of some good physics. The authors do not claim that many of these puzzles are original, though a number are; some indeed are old chestnuts, like the question concerning the furthest possible projection of the topmost brick in a pile. Many of the Problems certainly make you think. Perhaps not surprisingly, those on electricity and magnetism relate less well to everyday experience; compared to questions on other areas of physics they often appear rather contrived and are less readily distinguished from the type of problems that commonly appear in textbooks. The blurb on the back cover suggests that the Problems span a scale of difficulty that extends from those suitable for `an exceptional school student' to others that `some physics professors will find...challenging'. There is indeed a considerable scale of difficulty here, and as a result the level of the physics required for their solution is necessarily a bit patchy. The Solutions are explained in great detail, and that is a real strength. I particularly liked a couple of problems whose Solutions were based on dimensional analysis—and I wished there had been more such. In one case I found myself disagreeing substantially with the answer given; I won't spoil it by mentioning which one. But to see what others might think I posed this same question to a number of physics colleagues, producing a plethora of different answers—most qualified by the view that more information was required in the question. That, I think, is a criticism that might be levelled at a number of the Problems. It reflects a common difficulty—that for a good many of the questions it is hard to know the level at which they are meant to be addressed. Unfortunately, certain Problems are imprecisely expressed—whether through difficulties of translation from original Hungarian or through loose wording. One Problem begins: `A small object is at rest on the edge of a horizontal table. It is pushed in such a way that it falls off the other side of the table ...' Only in the Solution does it become apparent that the push is not continuous; less ambiguous wording might have been `It is given a push'. Together with others, I found at least one other problem sufficiently unclear that it was not until I looked at the Solution that I realised what the Problem actually meant. I have one other complaint, a fault that really might easily have been avoided. At the front of the book is a list of physical constants and a few other bits of data relevant to specific questions, a nice touch. But it is incomplete—for example Problem 134, `How high could the tallest mountain on Earth be?' requires information on the latent heat of metals that few readers could guess, nor even surmise the need for. This is not the only such example. In summary, the idea behind this book is a very nice one and, given the dissection these Problems are likely to receive as a result, the authors have done a brave job remarkably well. It is a book containing a number of gems and surprises; those of us who teach physics will undoubtedly be prompted by these problems to think up variations or extensions, and that too is a good thing.