studiot

This is a complicated way of saying that when an arm or wire etc is stretched in tension the work done = the strain energy stored = 1/2 stress x strain. This arises because the force required to "pull out" the object rises from zero at the outset to the full value at the end of deltaL so the average value acting over the whole distance is 0.5(0+F) = F/2. That is the value of the integral.

O is the cross sectional area, not the surface area.

Another way to look at the curl comes from fluid dynamics. If curl(F) = 0 then there are no sources or sinks within the domain of the field. Many problems can be reduced to 2D and for these curl(F) is a vector that points out of the plane of the vector field.

I wouldn't put to much emphasis on the idea of a speed limit. It is a consequence of Einstein's second postulate and introduces the equations x2 + y2 +z2 = c2t2 X2 + Y2 + Z2 = c2 T2 These allow us to solve for A, B and D. I have already connected time and space in the simplest way as a bilinear form in the time transformation equation. So I am really perhaps asking are there any other viable equations that could be introduced?

In considering the derivation of SR I wondered if the two underpinning concepts can be decoupled. Please note that this is not an attempt to debunk SR, rather an attempt to gain insight by strengthening it. The first concept (invariance of certain physical laws between inertial coordinate frames) is purely mechanical and does not depend upon the existence or non existence of any electric phenomena whatsoever. In other words it is not dependent on light or c or whether there is any light in the system under consideration. At the time of introduction of SR the only experimental data included light in the system, and Maxwell had developed his equations and related them to c, so it is not suprising that the second concept (invainace of c) was introduced. However subsequent observations in systems where light is not present (for instance cosmic muon extended decay time) do not conform to the purely mechanical Galilean relativity (in one dimension) such that X = x - vt Y = y Z = z T = t For translation as observed in two inertial systems, the first denoted by lower case, and the second translating at velocity v along the x axis relative to the first, by upper case . As all good physicists do in this situation we start by assuming the next simplest relationship between the variables X = A(x - vt) Y = y Z = z T = Bt + Dx and seeing if we can determine an A, B and D (I have avoided C to preclude confusion with c) to fit the data. Of course we know from history that the Fitzgerald - Lorenz transformations will fit the bill nicely, but as far as I can see, We still need some something even without their experiments. So I was wondering if the need for a 'speed limit' (though not necessarily its value or form) could be deduced from the first postulate alone?

For those who are also searching I think this refers to post#53 in the linked thread. hari123 welcome to SF, I look forward to some interesting posts, but please give a full reference in future to help others. Can you confirm I have identified the correct post?

Can you state Avogadros law? http://en.wikipedia.org/wiki/Avogadro's_law

Please be aware that GCSE is at a considerably more junior level. This is the specification for what the posters are doing The specification for the "controlled assessment experiment" is in section 3.6 here http://filestore.aqa.org.uk/subjects/AQA-4402-W-SP-14.PDF

This is the second post about this GCSE experiment we have seen in the last few days. Yours is better explained but still not fully so. I wonder if the question was not made clear to the students/ Your statement above means (to me) that you are looking to draw a graph of temperature change with amount of salt added, after averaging your results in each of the sets of three. Then you are probably expected to describe the shape of that graph to see if it is a straight line or some other shape. Is this how you see it?

Both experiment posters please note that when reporting experimental measurements you should report to a consistent accuracy (broadly number of decimal places) So if you are measuring temperature to 0.5 degrees then your measurement should be either 3.5, 4.0 or 4.5 for instance. You should not report 4 .0 as 4.

I would draw an averaging line through Li, K and Na and extend it to Cs. My graph shows it would give a better estimate if you could include Rb. The actual value can be looked up on Google or is on my graph for comparison.

Your first ionisation graph should look something like this. You should be able to pick out the trend.

Don't all cars have cranks?

Jesus also refers to himself as the Son of Man and in other ways, in the Bible. http://christiananswers.net/q-eden/son-of-man.html As to the "son of the holy ghost", there is substantial argument that the whole trinity doctrine was a later invention. https://www.google.co.uk/search?hl=en-GB&source=hp&q=when+was+the+holy+ghost+invented&gbv=2&oq=when+was+the+holy+ghost&gs_l=heirloom-hp.1.0.0i22i30l10.1625.6047.0.8890.23.18.0.5.5.1.219.2185.2j14j2.18.0....0...1ac.1.34.heirloom-hp..1.22.2155.8g-JZELoY8A

You seem to have moved on from your original question as to correctness in English to deciding that the use of the auxiliary verb to go is incorrect? English is characterised by the wide use of auxiliary verbs because the prefixes and suffixes are not much used as in other languages. The verb to go is a valid (and as you note common) auxiliary verb. But then 'will' is also auxiliary verb. I do not know of any prohibition on any verb actually being used as an auxiliary, though that would not be common practice.

I do not normally participate in religous discussions, but I guess that in Khartoum you may find background material more difficult to find than someone in the West, so I would like to offer a few comments. These are meant as pointers to help: I do not want to enter a protracted argument about them. To understand the Bible you need to know some things about it. It was not written all at once but is a collection of documents that were 'written' over a period of at least a thousand years. Individual parts were generally written up to several hundred years after a particular event and not generally by the persons themselves to whom the particular story is attributed. It was written in more than one language and on several occasions contains two quite different accounts of the same event. For instance many accounts in the Book of Kings (Ancient Greek) and the Book of Jeremiah (Hebrew). This is because when these were written there were two jewish communities separated by considerable distance. One was at Alexandria and spoke Greek, the other was in Jerusalem and spoke Hebrew. Jesus would have spoken Aramaeic. You are probably reading an English translation of one of these, which may have come from other languages before. So the bottom line is to try to determine for yourself (it is a very personal thing) what you think is 'true' and what has been changed in translation. London University offers Msc courses in something called Bible Study, by which they mean the study of the Bible as a collection of pieces of writing and how they came about, changed over the years, were inaccurate to start with or whatever. It was not the study of the religous content of that writing.

Well if you want to use comic book references I don't see how it pertains to special relativity. And it doesn't alter the fact that although we colloquially talk of the train 'being in one frame' and the platform being in another, the truth is that both are 'in' both frames. And I'm sure you know this perfectly well.

Funny I could have sworn it was a dimensionless number last time I looked. http://en.wikipedia.org/wiki/Mach_number

Um, how do you make that out? Does "mach 1" not have any units?

Hello Dekan, can you tell me what are the units (dimensions if you like) of "Mach 1" please? I'm sorry I missed your comment before, because of the page change.

There you go again. Introducing things I did specifically didn't to try to prove me wrong. I agree none of these things quoted have anything to do with what I said.

I consider it a great shame that as the only responder offering a way forward, both you and Christopher chose to reject what I had to say before I said it. I think the problem lies in a misunderstanding of terminology. So I asked a simple question to work through the problem from the beginning. The point is that the lightning (along with everything else in the universe) is not in any frame at all. This is a common turn of phrase that is actually wrong in strict terms. The lightning is in the universe, and every frame will identify the same point, but call it by different names. That is the whole point of Relativity. Consideration of this would lead to a resolution of your difficulties.

+1 Blimey, there must be something wrong here JC and I are in agreement!

I had a bad latex day recently so I have sketched the derivation out longhand. You should have enough to fill in the arithmetic, ask if there are any steps you don't follow.

It should be noted that this is not the method used for doppler satellite positioning.