Before you read this, I suggest you read posts 17.15 and 17.16. About 40 years ago, Brian Pullan was Head of the Department of Medical Biophysics in the University of Manchester. Late last year, he sent me a problem to think about – it’s in the next paragraph. An ideal plane flies in a straight… Continue reading 22.9 More about flying

To understand this post you need to be familiar with the contents of post 18.2. The picture above shows cables supported by pylons; each section of cable hangs from two fixed points. Between these points, the force of gravity stretches the cable so that it falls into a curve. Until the early seventeenth century, people… Continue reading 22.8 The catenary