Physics

Sharing thoughts based on my background in physics and mathematics.

When to say weight and when to say mass

By on Jul 21, 2009 in Physics |

I’ll try not to make this too much of  a rant. Having had a physics education over the years, I tend to pick up on people’s confusion of certain concepts. The most common one is that people don’t seem to be aware of the difference between weight and mass. Roughly speaking, mass, is a measure of how much stuff there is of something, and we measure it in “Kilograms“. Whereas, weight, is how much downwards force an object exerts due to its mass, and we measure force in “Newtons“. So you see, it is an invalid statement  to say that something weighs 10 kilograms. Also, when you weigh something, you’re determining its mass, by measuring its weight. Scales are calibrated to read off in units of mass, by now much weight/force is being exerted on them. Numerically, the difference between the weight and mass of a given object comes from the Earth’s gravity. Denoted “g“, it has a value of around 9.81 m/s2, that’s “meters per seconds squared” to you, which is the unit by which we measure acceleration. The formula to convert mass to weight is simply (yes there’s some maths!), Weight = Mass * Earth’s Gravity W = M * g So next time you’re talking about how much of something you’re getting, you’re talking about mass, unless you’re talking about lifting or carrying something, then it’s weight. When you read your bathroom scales, that number isn’t your weight, it’s your mass. If you don’t remember this lesson for yourself, then remember it for all us poor balding physicists who are slowly tearing our hair out at such misuse of...

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Movie Review: BLAST The Movie

By on Jan 21, 2009 in Physics |

A first for this blog, a movie review, again on the theme of the International Year of Astronomy. BLAST The Movie tells the the tale of an intrepid team of scientists hoping to travel back in time … on a balloon. Yes, it sounds like science fiction, but it isn’t. BLAST is an acronym for Balloon-borne Large Aperature Sub-millimetre Telescope. The BLAST project, lead by principal investigators, Mark Devlin and Barth Netterfield, was a project to both train graduate astrophysics students and to probe into views of the very early universe. How do we see back in time? Because light travels at a set speed, it does not instantly go from point A to point B. So, light from the most distant sources is also the oldest light. That is how we see back in time. This film was by Paul Devlin (any relation to Mark? Mark Devlin’s brother, thanks gmarsden) who has made two previous films (“Slam Nation” and “Power Trip“). While still paying all due attention to the scientific content, the documentary covers much more. In fact, it has many ingredients of a great drama. Much attention is given to Mark Devlin’s family and the effect that his prolonged absences have on his wife and two young sons. Also, some scenes are given over the two project leaders, Devlin and Netterfield, where they talk about science and their religious views. Devlin being an atheist and Netterfield being a Christian. All the while the spectre of failure hangs over the project as they hope they can collect the best astronomical data possible and then retrieve it from some of the harshest environments on Earth! However, the greatest moments of drama belong to the telescope itself, by virtue of old saying what goes up, must come down. Both of the BLAST flights lasted for six days, during which time it collected vast amounts of data, far too much to be transmitted to satellites. Therefore the data had to be recorded to hard drives instead, which meant that BLAST had to parachute back to Earth and be recovered. I shall not give away whether BLAST was successfully recovered or not from either flight though! All I will say, as above,...

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The Ever Expanding Universe in Modern Cosmology

By on Jan 12, 2009 in Physics |

Since 2009 is the International Year of Astronomy, here is something I thought I’d pull out of my personal archive. It is a dissertation I wrote for the third year of my MPhys, reviewing achievements in cosmology between 1916 and 1999. I invite everyone who reads this to add any achievements in cosmology since then in the comments! If I get enough interest in this post, I’ll consider writing an updated version. In the meantime, you can also find this dissertation at Scribd.com where you can read it as an embedded Flash book or download as PDF. Without further ado, I hope you enjoy reading this… The Ever Expanding Universe in Modern Cosmology David.R.Gilson Abstract An account of work done in modern times to determine the origin, behaviour and fate of our universe from theory and observation. We begin at the beginning of modern cosmology, almost the beginning of this century with the publication of General Relativity. We swiftly work our way through the corner stones of the century in modern cosmology up to current times with Alan Guth’s theory of inflation and the miraculous observations made by Saul Perlmutter’s group of many supernovae to infer universal expansion rates across the aeons. In the beginning… In 1916 Albert Einstein published his famous theory of General Relativity (GR). This theory gave the world a brand new way of considering the universe. Einstein postulated that space and time were simply ordinates of the same co-ordinate system. Furthermore that this space-time was warped in the presence of matter. Einstein based the geometry for his space-time on the geometrical structure of Riemannian space-time. Rienmann was the first person to publicly suggest that there exist a possibility of a finite and unbounded universe by treating space as a 3 manifold on the surface of a hypersphere (this was in 1857, the lecture was posthumously published in 1868). Einstein was keen to keep his theories consistent with the observations of the time. In 1917, the Milky Way galaxy (our galactic home!) was observed as the whole universe (given the range of the instruments of the time) which was not expanding or contracting. Since Einstein’s theory (and even Newtonian theories predicted the same thing, with hindsight)...

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A quantum leap in electrical energy storage

By on Jan 7, 2009 in Physics |

Something I heard about on Security Now (Ep.117) has got me rather excited and I wanted to report about it on here. Batteries vs Capacitors Currently, the state of the art for energy storage in contemporary electronic devices is Lithium Ion batteries. Despite the material used (the electrolyte), batteries are all pretty much the same, in as much as a chemical reaction occurs inside the battery which drives electrons that our electronic devices can use to do work. Rechargeable batteries use a reversible reaction, so that once you do electrical work on the battery (i.e. charge it), the reaction is reversed and can begin again to power your devices. There are a number of disadvantages to this. Firstly, because we are reversing the chemical reaction of the battery, it takes quite a while to charge them. Also, again because of relying on a chemical reaction, disposing is difficult because the contents are toxic. Also, rechargeable batteries degrade over time, so there are only so many times that you can discharge and recharge them. In electrical circuits energy can stored in components called capacitors. Capacitors aren’t used in place of batteries because the amount of energy you can store for a given size (i.e. their energy density) has been tiny. A little bit of physics for you here, which you need to know to understand the significance of what I’m leading up to telling you! The standard unit of capacitance is the Farad. Most capacitors you come across are rated at the micro Farad level (i.e. a millionth of a Farad), ranging up to a few hundred micro Farads. In my personal experience I have only seen 1 Farad capacitors for car stereo systems, although the things are massive and expensive. Capacitors work differently to batteries. The general model of a capacitor is two parallel metal plates separated by a non-conducting material called a “dielectric“. The idea is that when you apply a voltage to a capacitor no current can flow through, but instead the electrons pile up at the cathode and create an electric field within the dielectric. Therefore, energy is stored in a capacitor as an electric field. Hence, a desirable dielectric material is one in which electric...

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Laying Schrödinger’s Cat to rest

By on Dec 11, 2008 in Physics |

We’re talking about Quantum Physics today, and how one of the most difficult to understand concepts is made twice as confusing as is necessary by one of the most poular popular-science gedankenexperiments (that’s German for “thought experiment”). If you don’t know about Schrödinger’s Cat, then this post probably isn’t for you. Although if you are a fan of physics or popular science (for which I applaud you), then read on. Firstly, I’m going to outline what the “Schrödinger’s Cat” gedankenexperiment is actually meant to demonstrate, then once we understand that, I’ll look at what’s wrong with how the gedankenexperiment is presented to the public. The weirdness of elementary quantum theory In quantum mechanics, we find that particles (which are on the quantum-size scale) seem to be able to be in two places at once (position being just one example). Certainly this is WEIRD and counter intuitive. Don’t feel dim for wondering how this can possibly happen, never feel dim. In fact, everyone from the physicists who came up with all this, to the best minds we have today, still don’t understand the mechanism by which this happens. The important thing to keep in mind, and to some this may be intellectually unfullfilling, is that as scientists we come up with a theory and then check to see that it agrees with nature (i.e. experimental observations). We can never truly know if our theories are telling the real truth about nature, all we can know is that our theories describe the behaviour of nature, within the limits of our technology and ability to test that theory. In quantum mechanics we have a terminology, in which we say a particle is in a “superposition of states”. This simply means that we think of the particle having more than one physical state superimposed upon it. This could be more than one position, or more than one energy, etc. Again, this is strange, weird, counter-intuitive. However, we find that we must accept it, because there are experiments that test for this very behaviour and they all come back positive. I’d love to explain the experiments, but then this post would end up being three times as long as intended! What causes this superposition...

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The boundaries of language

By on Nov 5, 2008 in Physics |

This is a reply to a blog post called “Is astro-physics hindered by our language?” by Nate Lanxon. It is indeed an intriguing question, and it is certainly not limited to astrophysics. The following scenario came into my head that lead to this thought. Let’s say an English speaker heads to Japan and wants to tell a Japanese speaker, for whatever reason, that he is happy. Saying “I am happy,” means nothing to a Japanese speaker, just as saying “Shiawase da naa,” would mean nothing to our English speaker. So instead, he simply smiles widely. The emotion is conveyed and, more importantly, it’s understood. And without uing the languages we’ve developed for ourselves. To stretch the point even further, I’d argue that the smile would be meaningless to a being from another world. The point here though, is that language and facial expressions are the same in that they are subjective reference terms. I would go on to say that the only truly objective language that could be shared across the universe is mathematics. Any sentient being must have the ability to count. Even if you have two beings that are completely alien to each other, they should be able to agree how to count. From counting, the whole of mathematics then flows, the only hurdle would be the notation. I think of the word ‘infinity’. To me, infinity isn’t a thing; it’s not a tangible object. Rather, it’s a word we’ve slapped on something that doesn’t exist, so we have a way of talking about it as if it did. Now I don’t believe in physical infinities. I don’t like to think the singularities at the centres of black holes have an infinitely huge gravitational pull. I’m not suggesting the gravitational pulls are not there — obviously — or that they don’t function exactly as they appear to function, but that we’ve slapped a word around them that’s blurring our understanding. Some physicists do believe in “singularities“, they accept the infinities in our theories. I’m not one of them, I side with Dirac who I believe is to have said: “if you have singularities in your theory, then your theory is wrong“. However, by virtue of the mathematical...

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