The Dragon Capsule from SpaceX has just docked successfully with the International Space Station. It carried four astronauts to the orbiting space station; they will live there for the next six months. It was reported by the Guardian here. Looking at the picture in the report, I was struck by how close the Earth seems. […]
Chirality – an open problem in chemistry
Most scientific research is directed towards answering a question. Fortunately for researchers, there are a lot of questions in science that don’t yet have answers, some of which are quite fundamental. If you do a quick google search for ‘unanswered questions in science’, for example, you’ll come across questions like: What is spacetime? What is […]
Picturing sound
This is a post about a possible misconception about sound that can be gained from a common method of drawing sound waves. Sound is caused by vibrating objects. Those vibrations cause disturbances to the particles of the surrounding medium (air, for example). Those particles disturb their neighbours, and the disturbance propagates outwards as a wave […]
Why u-v lights look cool
Why are ultra-violet lamps used at parties and discos? Because they create an appealing effect that is different from illumination by normal white light. It’s not just that purple is a nice colour. You could use a purple light for that. It’s that white clothes look (a) white, when they should look purple. I’ve written […]
A matter of perspective, part 3
This is part 3 of a blog using artistic perspective to provide a context for discussing the relationship between special cases and general laws. You can find Part 1 here, and Part 2 here. Why are the lines straight? Imagine standing in front of a ruined section of the Great Wall of China, or Hadrian’s […]
A matter of perspective, part 2
This is part 2 of a post using artistic perspective to provide a context for discussing the relationship between special cases and general laws. You can find Part 1 here. How far apart are the vanishing points? In two-point perspective, the spacing of the vanishing points reflects how close you are to the scene. In […]
A matter of perspective, part 1
What this post is about Someone recently asked me how to draw in perspective. That was a mistake, because I am the living refutation of the encouragement “Everyone can draw.” Still, I guess the idea was that I know some physics and so must understand how 3D geometry works. So I explained about one-point and two […]
Modelling exponential change
In the popular media, you often hear the phrase “the ‘something-or-other’ has grown exponentially.” Quite often in such situations, the word ‘exponentially’ is used imprecisely to mean ‘quite a lot’ or ‘rather fast’, but in science it has a very specific meaning. Exponential changes happen when the rate of change of a quantity is proportional […]
Radiation dose. Or, ‘what’s a millisievert?’
Fukushima in Japan has become newsworthy again recently. Many residents have been allowed back to their homes. In January 2019, Scientific American reported that radiation: “in some places continues to measure at least 5 millisieverts (mSv) a year beyond natural background radiation, five times the added level Japan had recommended for the general public prior […]
And while we’re here, Newton’s second law isn’t F=ma either
My last post on how [latex]V=IR[/latex] is not Ohm’s law received some comments. @dodiscimus said: “And [latex]F=ma[/latex] is not Newton’s 2nd law. Your next post?” I’m quoting him to: give him the credit for having the idea and spotting the similarity (see later) share the blame – otherwise people are going to think all I […]
Why V=IR is not Ohm’s Law, and why that matters
I have lost count of the number of times I have heard people say that Ohm’s Law is [latex]V=IR[/latex]. I have seen it in lots of electrical training materials. This post is to explain that Ohm’s Law and [latex]V=IR[/latex] are not the same thing, and that the difference matters; thinking they are the same is […]
Relative atomic mass – a question…
I was led to thinking about relative atomic mass the other day, and asked myself a really simple question that I couldn’t answer. I was slightly embarrassed that (a) I didn’t know the answer, and more importantly that (b) I’d never considered the question before. The question is “when/where do these numbers apply?” Let me […]
The world’s oldest periodic table
Recently, the BBC reported that “a periodic table found during a laboratory clear-out at the University of St Andrews is believed to be the oldest in the world.” Here it is, together with the link to the original article. There’s loads of interesting and thought-provoking science in this periodic table. Hence this post. It would […]
How does the Richter scale work?
In our previous post, we described the use of decibels as a unit of ‘sound level’, and talked of it as a logarithmic scale, one in which equal increases represent equal multiplications of the quantity represented. In this post, we will look at another logarithmic scale, the Richter scale for earthquake magnitudes (seismologists may be disgusted […]
What is a decibel?
We have probably all seen charts of the decibel scale like the one below. But unless you know how the scale works, you might be led to think that a rock concert is twice as loud as a conversation. And instinctively, you might realise this cannot possibly be the case. This post aims here to […]
The miracle of hearing
As a child, I was oddly fascinated by how ears work. I used to ask “How can we hear two things at once and tell them apart?” I still think this is a much better question than it is given credit for, one that people rarely stop to think about. And it is what this […]
A primer on the standard model (Part 2 of 2)
This is part 2 of a primer on the standard model. If you missed part 1, you can find it here. The eightfold way Let’s begin with the mesons (pions and kaons). They have charges of +1, 0 or -1, and strangenesses of +1, 0 or -1. We can draw a chart with strangeness on […]
Particle physics – a primer on the standard model (Part 1 of 2)
Making sense of the ‘particle zoo’ This is a great decade for the popularisation of science in general, and physics in particular. The detection of gravitational waves by LIGO, and the books of Carlo Rovelli, are just two things that have caught the public imagination. But nothing has done more in this regard than the […]
Atomic structure and the periodic table (full version)
In this article, we hope to develop an understanding of atomic structure and the periodic table, from the beginning of secondary school/junior-high level, to first/second year undergraduate physics/chemistry, via one fictional conversation. This was orginally put online in six parts – you can still access those parts separately if you prefer from our blog page. […]
Atomic structure and the periodic table (Part 6 of 6)
The final episode of our article, in which we try to develop an understanding of atomic structure and the periodic table, from the beginning of secondary school/junior-high level, to first/second year undergraduate physics/chemistry, via one fictional conversation. Find Parts 1 – 5 on our blog page. Sigrid has just asked Sally whether ‘l=0’ corresponds to the […]