studiot

Here is what I think is a clearer example than your honey trap. Suppose you play one-handed catch with your little sister, and throw the ball to her 1000 times. Suppose she catches it 700 times with her left hand and 300 times with her right hand. Then the probabilities that she will catch it left handed are 0.7 and right handed 0.3. The implication that can be drawn is that she is left handed and that the hand she chooses to catch with is not by chance. Now suppose the outcome is different. This time she catches the ball 500 times with each hand. Now the implications are that she is ambidextrous and that it is pure chance which hand she uses to catch a particular ball. So in outcome (2) she catches the ball purely at random with either hand. but in outcome (1) her choice of hand is not random.

Can't agree with this, they are not the same, even in scientific English. Function, please look at my edit to post#4. To further continue, random ( in the statistical sense) implies that the probabilities are the same for all outcomes. It the probabilities are not the same it implies that there is some preference or selection or other driving agent involved.

Good morning, I typed out a reply, but when I look back here it was gone. Sigh! I think your difficulty is due to language differences. In English chance and probability both have multiple meanings. In particular chance usually conveys the idea of 'without apparent cause or direction', whereas probability compares different outcomes, edit : regardless of cause Scientific English has taken one particular meaning for both chance and probability and codified this. The particular meanings codified are those stated above. You should also look up the words, fluke and random. Both are connected to this subject. Unfortunately the scientific definition of random has (at least) two different meanings.

I am sorry that I was not able to write my point in a way that could be understood, for you have, unfortunately, completely misunderstood it. I take full responsibility. I have neither wish not intention to discuss the capacity of the human mind. Yes I think 'what is...?' questions are generally classified as within the province of philosophy by this Science Forums. There have been many precedents for this. There is a perfectly respectable philosophy section at SF. But your thread is in the Physics section, so you are expecting a Physics answer. The point I am trying to make is that before you can discuss whether space is empty or occupied you need to specify what you mean by space. This is not an idle observation since it begs the question "is there a entity called space, separate from the entities within it?". This is most definitely a philosophical question since I am asking "Does the region defined by our coordinate axes have an existence of its own and, if so, is it continuous or granular. Is it isotropic, homogeneous and what are its other properties, as distinct from the properties of anything it contains.?"

Perhaps you are looking at things from the wrong end of the telescope? 'is' is the word of nightmares. what is energy? What is matter? What is space, empty or otherwise? I have noticed that those who keep demanding to know 'what is .... ?' drive themselves to distraction since this question usually has no answer in Science. I prefer to use the view that Science 'offers the following model', given the particular entities or quantities. We can then compare this model with observations and amend it if necessary, without struggling with answering the philosophical question 'what is (empty) space?', thereby retaining our sanity. And yes, I know I've used the word is many times in my post.

Hi, Ilya and welcome. British English is taught differently from the descriptions already given. The language is formally separated into two subject, english language and english literature. Much of what you seek is incorporated into the english language syllabus. In this syllabus the student is taught to read and understand what someone else has written and to be able to reproduce the meaning in his own words. He is also taught how to produce subject specific writing for example letters, obituaries, recipes, and so on. He is taught how to write to a particular length. Additionally report writing skills (including powerpoint) are taught within science and engineering subjects themselves. There are two levels of course/exam That taken about at age15/16 - the GCSE And that taken the following year - the GCE AS level Here are the specifications for the AS level note particularly section 4.1 B "Writing for specific purposes" http://www.wjec.co.uk/uploads/publications/3878.pdf There are also international versions that also come in two flavours The iGCE and iGCSE for English as a first language The iGCE and iGCSE for English as a second language, which is probably the one you are looking for. Cambridge University is particularly strong in this area, although googling the above phrases will find others. http://www.cie.org.uk/programmes-and-qualifications/cambridge-igcse-english-second-language-oral-endorsement-0510/ Finally Bill Scott has written a particularly good book called "Communication for Professional Engineers" This was produced for and is published by Thomas Telford, the publishing arm of the Institution of Civil Engineers.

Dark matter has been proposed to explain deficiencies in astrophysical calculations. That is it has some interaction with the rest of our universe, just not a visual one. So, if dark matter does exist, then is is certainly not undetectable. Anything that 'exists' but has zero interaction might just as well not exist, as far as we are concerned, and would be truly undetectable by us.

studlot....I agree that the fish can sense the water due to frictional contact and (reaction) pressure...I never said that a fish cannot sense the water...but rather...if the water was pure...that the fish could not see the water. The point of this metaphor, the question I am raising in this post, is what is the "evidence for empty space"? I am not asking this question in a small way. I am not asking about the idea that there is less empty space in the universe than previously considered....I am asking this question in terms of...how do we know there is any empty space at all. The fish is "blind" to the water it swims through. Are humans "blind" to what fills what is considered empty space? I was rather gently observing that I find your proposal a bit like complaining you cannot see sound, or taste light. You are simply be focusing on the wrong sense. That is why we (and fish) have a bunch of senses to interact with our environments and our brain selects the appropriate one for the job in hand.

So you calculated that the entropy change is zero, since that is your criterion for reversibility. Would you mind showing your working? Can you state exactly which law and how?, the above is oft quoted hand waving. Actually you are the one who has missed my point. If you include the surroundings (rest of the universe) in the 'system', then there is room for only one system in all the universe, so every system is identical.

Well I was trying to hold a conversation to help you along your journey, but the time gaps were rather large. Do you see that to complete this question you need to calculate both the first law work and heat changes? You also need the fact that one version of the universal gas law is that the internal energy of a perfect gas depends only on temperature. You need to combine the first law with the gas law and your mechanical balance from parts A and B to form a single equation to complete the rest of the problem. Note in setting up the mechanical force balance to choose a consistent sign convention for up and down (have you done this ?) If this is too late, good luck with your submission.

This new homework question provides an object lesson in classical four-law thermodynamics as to why you need to separate a system from its surroundings by its boundary and why you need reversibiltiy. http://www.scienceforums.net/topic/84056-thermodynamics-and-gas-law-problem/ Of course if you take the view that the whole of the universe is 'the system' then there is only one system in the universe, which is the same for every problem. So bothering to even state the word system, let alone specify it, is pointless. We also seem short of others prepared to help in the thermo homework section?

Yes the atmospheric pressure exerts a force on th top of the piston. You say the piston is in equilibrium. so parts A and B are not really thermodynamics at all, just basic mechanics. Think of the piston as a free body diagram and balance the vertical forces. Remember that the pressure inside the cylinder is absolute not gauge. Now how about answering my question on C?

You have missed a term that adds to the downward force in part A For part B you have added an unecessary term. Why do do think the volume of gas would double? What law, under what conditions says that? Understanding why this is not so is the key to part C

Do you normally feel the ground under your feet as you walk? Of course the fish can sense the water in just the same way since both your walking and the fish swimming rely on the frictional contact and (reaction) pressure.

Here is one way to get the best of both worlds. Use a docking station. The laptop can be seen mounted on the docking station, where it just clicks into place and provides desktop like facilities. The special purpose mouse can be seen in the apple standing on one of the laptop pads.

That was meant to mean that there are no dissipative processes.

Interesting, thank you. I know the prevailing winds are westerlies but I wonder if any of the tectonic activity in Iceland has anything to do with this?

Now that I am back home, let us discuss the following closed, isolated system. Consider an adiabatic cylinder containing a frictionless adiabatic piston separating the cylinder into two chambers, each containing a compressible fluid, so that the piston is in the equilibrium position. Let the piston now be mechanically displaced from its position and then released. Are the subsequent changes reversible or irreversible and what is the entropy change of the overall system?

The 'politics' comment was about the obsolescence discussion, planned, built-in or just plain there, which is what my link is all about. But yeah, whatever, computer help is good too.

Hazel, your thread should be in politics or in the lounge, like this one here. http://forum.allaboutcircuits.com/showthread.php?t=95669&page=18 When I was young, one of the legacies of Birmingham being the (metal)workshop of the world was that if you needed a piece (or a thousand pieces) of any type metal in any shape of form, there would be a dozen back steet companies who could supply off the shelf or make cheaply to order. Small companies that had grown up supplying to the big ones. which supplied to the world. Similarly in London, where I lived, there was a place where you could obtain nuts and bolts for any thread ever made. The owner made his fortune out of this simple supply. Nowadays the the West has handed manufacturing on to others, these paragons have all gone and obtaining even simple things is difficult. Sales clerks these days usually don't even know what you are asking for at component level. go well

Ask for some help, instead of bleating. If you were to tell us the details, I might be able to offer some suggestions, as might others. For instance I often buy broken laptops on Ebay - that is broken except for the part I want - this can often make an economic repair. Since yours has a mobo failure I would suggest looking for one with a smashed screen, but functioning mainboard. These can be had in the region £25 - £75 in the UK, probably the same number of $ in the US.

Windows has lots of options to help make life easier. Look at the accessibility options in the XP control panel Also look at the magnifier http://windows.microsoft.com/en-GB/windows-xp/help/turn-on-magnifier

The screen size you can plug into a laptop is not limited by the laptop. Many laptops have an HDMI port which carries both high definition television / video and sound in one cable. Very few desktops have this. Touch screens have not been a success for desktops, but are readily availabale in laptops and tablets. If you buy a laptop beware of closing it with an object such as a pen inside. Broken screen replacement costs run from about £90 to about £350. Be careful of the power connector, they are overweak and the laptop usually has to be dismantled to replace. A good practice is to place a weight (book etc) onto the cable to prevent the full weight of the power supply/lead/interference suppressor dragging on the conputer jack. Do not obstruct the air vents. Many laptops have air vents on the undersurface. I recall one client who burnt out his laptop by working in a heavily upholstered armchair and resting the latop on the padded arm, thus blocking these vents. On the other hand working on a laptop can be worse for your health, so much so that there is a (much ignored) EU health & safety directive that requires workers to be provided with separate screen and keyboard to avoid RSI and eye problems. You are better off with separates if working for long periods, you can also adjust the chair to suit as well. Oh and on screen print size can be adjusted in most programs by adjusting the zoom on either laptops or desktops.

Nicholas, you are obviously keen but have not yet met many of the deeper points and connections of mathematics. These are not introduced in courses taught at your school level and, I'm sorry to say, that some of the groundwork that used to be taught is missing today. So you will have to seek out some of this for yourself. That can be an exciting journey for those who are interested in such matters! You need to fully understand the difference between an equality and an identity. They are different, although we usually use the equals sign for both. Similarly you need to fully understand what is meant by the statement; "X satisfies this equation or that condition". Also important is what mean when we say 'solve an equation'. In elementary mathematics, particularly applied maths or physics etc, this often means "plug in the known quantities and find the unknown quantity" Otherwise called 'plug and chug' Schrodinger's equation is an example of a type of equation that has an infinite number of solutions. But we do not use Schrodinger's equation in isolation, a proper description also comes with some (a set of) 'boundary conditions'. These boundary conditions are additional mathematical statements, which may be equations to solve in their own right, which allow us to pick out a solution from all the infinite possibilities, appropriate to the system in hand. This combination of a key equation, statement, principle, law, or theorem with other information is very common to the point of being the norm. Having worked through all this we extract from the Schrodinger equation, along with the problem boundary conditions, a function or functions functions. Somtimes this function is such that it obeys an uncertainty principle. Note this idea of uncertainty applies to many equations,even simple algebraic ones. For example the equation 3x2+8x+6 = (x2+4x+1) +(2x2+4x+5) is infinitely uncertain since it is true (satisfied) for any or all values of x. (Note this is actually an example of an identity that I mentioned earlier) Whereas the equation 3x2+8x+6 = 2x2+5x+4 is precise (certain) since it is only true for two specific values of x, namely x= -1 and x=-2. (note this is an example of an equality).

In line four if you multiply deltaH /R into both terms in the bracket, you recover line 3 and remove the bracket. All they have done is the equivalent of {-3/2a - 3/2b} take out the common terms 3/2 leaves 3/2{-1/a - 1/b} can you see it now it is simple algebra. Sorry I can't do the latex at the moment.