In posts 20.2, 20.3 and 20.5, we thought about stretching a long, thin wire. This post continues the topic. But it is about the work done (post 16.20) in stretching the wire and what happens to the resulting potential energy (post 16.21). When a force stretches the wire, it moves its point of application and… Continue reading 20.6 Elasticity
Before you read this, I suggest you read post 20.2. Let’s return to stretching the long, thin wire of post 20.2. In posts 20.2 and 20.3, we neglected that the wire becomes slightly thinner as it gets longer. The reason for thinking about a long, thin wire was that this effect is not easy to… Continue reading 20.5 Poisson’s ratio
Questionnaires are often used in medical research to find out what people know or believe. Studies based on questionnaires can be very informative but need to be read critically. https://oncologypro.esmo.org/Meeting-Resources/ESMO-2017-Congress/European-survey-of-907-people-with-cancer-about-the-importance-of-nutrition is a report presented at a meeting of the European Society for Medical Oncology. It concludes that most of the people with cancer who participated… Continue reading 20.4 Questionnaires and response rates
Before you read this, I suggest you read post 20.2. Hooke’s law is named after the English scientist and architect Robert Hooke (1635-1703). Most textbooks give the impression that Hooke’s law is important for understanding how objects deform when subjected to tensile stress. If you continue to read this post, you will see that I… Continue reading 20.3 Hooke’s law
Forces change the state of motion of an object (post 16.13). But, in post 16.50 on springs, we saw that forces could also change the dimensions of objects. A spring can be stretched by a force (a tensile force) or compressed by a force (a compressive force). This effect is not restricted to springs –… Continue reading 20.2 Deformation of objects – stress, strain and Young’s modulus
This post was prompted by something written in the art magazine Universal Colours (http://www.eu-man.org/magazine/issue903.df). The article states that, “Modern science uses mathematics … for proving … suppositions in science”. Mathematics is not used to prove scientific ideas; it is used to develop new ideas from ideas that we believe to be true. This is not… Continue reading 20.1 Mathematical proof and science
Maxwell’s demon is an early example of a “thought experiment” (see post 19.26). The Scottish physicist James Clerk Maxwell thought about two samples of a gas, each containing containing fast (red in the picture) and slow (blue) molecules, separated by a wall. He supposed that the wall contained a tiny door that could be opened… Continue reading 19.30 Maxwell’s demon
My posts on quantum mechanics have made a number of statements that not everyone would agree with: That particles, like electrons, can behave as particles or waves (wave-particle duality, post 19.25) That we cannot simultaneously know the position and the energy of a particle, like an electron (Heisenberg’s uncertainty principle, post 19.26) That a wavefunction… Continue reading 19.29 Interpreting quantum mechanics
Before you read this, I suggest you read post 19.27. Schrödinger’s equation, above, describes the motion of a particle (like an electron) in terms of its wavefunction, ψ (post 18.10), and energy, E. Here ∇ is the Laplacian operator (post 19.12), m is the mass of the particle, h is Planck’s constant (post 19.19) and… Continue reading 19.28 Solving Schrödinger’s equation
Before you read this, I suggest you read posts 19.12 and 19.24. If you’ve heard of “Schrödinger’s cat”, and didn’t understand what it was about, I suggest that you forget it – it won’t help you to understand how quantum theory (post 16.2) is used to explain things. But Schrödinger’s equation is very important –… Continue reading 19.27 Schrödinger’s equation
