studiot

I meant to ask if you were just asking questions. I don't understand this. Who hasn't answered what? I answered this in post#25 with two examples. You cannot seriously expect me to list a measurement method for every possible non material noun? Whether there are any observers for any phenomena does not alter their reality. This is a statement not a question, but I think I agree with it if by something physical you mean the same as I mean when I say a noun describing something material. I offered a counterexample to those who believe that real and material are synonmous. They are not. Nouns can be material or non material. The opposite of real is imaginary. A 25 foot spider is material and imaginary. A 55 week summer holiday is non material and imaginary. I'm sure you can think of plenty more examples.

You may find that masers more generally make your question obsolete. Look particularly at the part entitled 21st century developments. http://en.wikipedia.org/wiki/Maser

I'm sorry, Sam, I still don't understand your point or points, in relation to either my post or the thread topic. Sensei, the question was about reality, not faulty perception of reality. If I miscount the number of £100 notes in my wallet and find there are only 24 instead of 25 it does not alter the reality to be found in my wallet by any competent mugger. I have noted that there are nouns that refer to material objects and other nouns that refer to to non material objects. I offered the proposition that one type is as real as the other, with the proof to be founf in post#22

Yes the book is unclear and you have correctly deduced that for a non spinning spherical Earth the weight would be the same at the poles and the equator. For a more complete derivation you need to think in three dimensions. Firstly the geometry. In fig1 any point of the has latitude [math]\lambda [/math] on the surface of a sphere of radius R. If we take horizontal (East-West) sections as shown by the dashed line through the point on the surface we generate a smaller circle of radius [math]{R_\lambda }[/math]. This has centre [math]{C_\lambda }[/math], as shown in fig4 beneath. It is important to remember that the centripetal/centrifugal action takes place in this plane and is not directed towards the cente of the Earth. This is shown in fig3 In fig2 we see that the acceelation due to gravity is directed towards the centre of the Earth. This acceleration is the same everywhere on the surface of a rotating or non rotating spherical Earth. The accelerations are vector quantities and combine vectorially so the component of the acceleration due to the rotation is [math]{\omega ^2}{R_\lambda }\cos \lambda [/math] ie [math]{\omega ^2}\left( {R\cos \lambda } \right)\cos \lambda [/math] Now the object of mass m is resting on the Earth's surface, but it is not in absolute equilibrium since it is spinning with the Earth. We can reduce it to euqilibrium by introducing the fictious centrifugal force which acts outwards and opposes the force due to gravity or the weight of the mass. This is shown in fig 6. This centrifugal force reduces the weight of the mass by the equation shown at the bottom. So the apparent weight as measured by any device that does not balance weights eg a spring balance will be lower than that measured by a weight balance eg a beam balance since the weights in the beam balance are affected the same as the mass.

Sam, I can't make out if you are agree or disagreeing with me? I can tell by looking at a stone or star shape if it is round or pointed. I can say an apple is round, but a banana is stick shaped. I said that science devises methods of measuring the roundness or angularity or other shapes, where the assessment is more vague in common English. Furthermore I said that If the object exists, its shape exists. I can prove that by tracing round the outside and removing the object from the universe (ie destroying it) But I still have the shape. Again maths provides us with ways of measuring. It is not usual to describe a circle by the emthod of envelopes, but it can be done. Such dual methods provides useful alternatives in some situations.

Does this help? http://curious.astro.cornell.edu/question.php?number=310

I am not sure what method you want to use. If you are measuring the time interval between sending and receiving a signal than yes the longer the time interval the more accurately you can measure it (within reason) So a slower signal would give more accurate distance reading if you knew both signal speeds to the same accuracy. If, however you want to use the wave properties to measure distance then speed is immaterial. What counts is the wavelength. the shorter the wavelength the finer the resolution of your measurement.

You guys are arguing with your instincts, not your intellects. In ordinary English we can identify non material nouns ie separate out some quality from an object eg roundness or hardness. In science or maths we can be more specific about these and even develop ways of quantifying these non material nouns. Reality includes both material and non material nouns. Neither type is more real than the other. In fact as soon as you have a single material noun, that you can declare to be 'real', I can find a non material property it possesses which must therefore be as real as the object itself.

Shouldn't that be [math]\frac{{{\partial ^2}E}}{{\partial {x^2}}} = \frac{1}{{{c^2}}}\frac{{{\partial ^2}E}}{{\partial {t^2}}}[/math] I do not quite understand the point you are trying to make, but are you trying to suggest that your sequence of maths leads to the paradox that the j unit vector is the same as the k unit vector (equation 5)? You cannot perform a one dimensional analysis. EM waves require three dimensions because the E part is orthognal to the B part and both are orthogonal to the direction of propagation. Would you like me to work through the derivation with you and explain each step?

Since you have invoked the dreaded 007, to quote him And yet in another thread you were adamant that your eye was the only true origin and continued quite a lively discussion about this assertion. You cannot have it both ways. I doubt that you have any idea what I was alluding to when you made the above response, Yet you did not ask But in IMHO the real issue is as 007 says, you do not listen to any one else. A discussion involves exchange of ideas: I have acknowledged your good ones, but you have steadfastly refused to listen to any of mine or from anyone else. If you could do this there is a real danger that you might learn something new and of possible value.

People are afraid of quantum mechanics because it is given some sort of mystic significance and the student is told "It is different" It is not different at all. Quantum mechancis simply picks out certain values as allowable and discards the rest. This arises quite naturally from normal continuous mathematics. Consider the function f(X) : X2 -1 X can vary from minus infinity to plus infinity. That is it can take on any value at all and the function is continuous. Whatever the value of X I can calculate the value of the function. Now let me state f(X) = 0 ie X2-1 =0, then there are only two values of X that satisfy these conditions. So from a very simple continuous function I have moved to a quantised version.

Fred, I find your idea of a frame of reference far to limited and constraining. Why should it be constrained to someone's eye? What if I wished to consider the mechanics inside a solid body? Where would I place my eye? I say this because there are 'preferred frames of reference' in such circumstances (ajb has already referred to these). The OP has perfect, I agree with ajb preferred is a better word - nothing is perfect. In the example I just gave we call these preferred axes 'Principal Axes', and the (preferred) frame of reference is defined by these.

Let us look at English, which offers the classification Concrete Nouns such as , well concrete Abstract Nouns such as symmetry. The first is what one might identify with 'Real' in the OP but is far from fundamental in Physics, although it has a place. The second is non real, but is certainly fundamental in Physics. But I agree with swansont, a bear can overclassify.

+1 Cool links, Mike

I'll just leave this little tantrum for the mods to sort out go well

Well I don't know, I can't get any LaTex to work on this site, I use MathML. But some seem to manage, by putting it into a script window. Ask a mod.

It says the spell is too long

The statement was pithy, too the point, accurate. Agreed 110%. What more is there to say?

So can you write down the Weyl Tensor, without making any reference to a varaible t (actually partial d/dt) called time?

No. In the Millikan experiment you make two measurements on each drop individually. Calculations are then performed on each drop individually. You measure the terminal velocity (by timing its passage past a scale) without any applied electric field. Then you measure it with the field applied, or you measure the field to halt the drop falling. The first measurement is to determine the radius of the drop. The second is to determine the charge on the drop. Note that in the experiment the drop size can vary continuously over a range of values. It is only the charge that turns out to be multiples of one basic unit. The value of this basic unit is then averaged from all the individual calculations (Millikan originally made thousands).

A few corrections are in order here. @Mike SmithCosmos The corpuscular theory of light was propounded by Isaac Newton in 1660, who coined the term corpuscular. His 'corpuscles' were able to explain reflection and refraction Huygens was a contemporary of Newton who first proposed a wave theory, in 1680. Although it was known that Snell's law could distinguish between the proposals by measuring the speed of light in dense media such as water, methods were not then available to make the measurement. Foucault achieved this in 1850 and showed that, for speed at any rate, Huygens was correct. Thomas Young developed interference experiments (1800) and theory that demonstrated behaviour only available through wave motion. Following the subsequent discovery of phenomena (photelectric effect: Hallwechs 1888, Lenard 1902) only availble to corpuscular motion Einstein revived the corpuscular theory by naming the corpuscle a photon in 1905. @compernicus1234 I have 1865 in my reference. James Clerk Maxwell, A Dynamical Theory of the Electromagnetic Field, Phil. Trans.Roy.Soc. London, 155:459 (1865) Here is an extract from the introduction You seem to be concerned with Faraday's and Ampere's experiments. You see from the extract above that Maxwell was happy to acknowledge the work of others, but his introduction of an equation to describe an induced magnetic field (induction) was a theoretical extension of Ampere's law, by the introduction of what Maxwell called "displacement current". Ampere [math]\oint {B.dl = \left( {\mu \int {J.ds} } \right)} [/math] Maxwell [math]\oint {B.dl = \left( {\mu \varepsilon \int {\frac{{dE}}{{dt}}.ds + \mu } \int {J.ds} } \right)} [/math] The additional term in the Maxwell equation gives the magnetic field induced by a changing electric field You should note that his was a field theory. Faraday's law of inductiuon is a current theory, as is Ampere's Law.

Well Captn Panic did ask what you are trying to do. If you can't control the pressure in the tank, the only other place you can control it is in the piping. This means that you don't take the fluid from the outlet directly, but lead it in some sort of pipe that has a flow rate controller attached. This may include a pump.

I don't think you have quite understood what Cpt Panic was trying to tell you. The flow rate depends on the pressure pushing it along and the size of the minimum cross sectional area of pipe. It does not depend directly the volume available from the reservoir tank. Your 'flow restrictor', valve, tap, or whatever you want to call it adjusts the minimum pipe area to provide the desired flow rate for a given pressure. The flow restrictor does not control the pressure. That is up to you and how you arrange your pipework and tank. My hospital example they put the tank(Bag) up a large height in relation to the size of the bag so this mounting height controls the pressure. Captn Panic offered another way - to have a large flat reservoir. There are yet other ways some mechanically quite complex. But to have constant flow you need to arrange constant pressure.

If this is a school project, go to your local hospital (possibly the medical physics dept) and ask for someone to show you how I V and syringe pump drivers work and flow contollers work. I'm sure you will find some useful practical help there.

Here are some ideas that may help you. Mathematically we collect together all the objects that have some property(ies) of interest in a set we call a 'space'. These object obey desired rules of combination. We do this because we want our maths to benefit from any useful common properties For instance 'closure' on our space means that for some operation, F, between any members (A, B and C) of this set or space F(A,B) yields another member of the set. For example the integers are closed under addition. Adding any two integers will always result in another integer, not a fraction or any other sort of number. This may seem trivial, but it is an incredibly powerful idea. It is what we use to prove the existence and uniqueness of solutions to equations. If our set contains functions, we can select functions that are solutions to an equation of interest and combine them to find other solutions. If we have a second set of constants (a, b, c etc) and our objects combine according to the rule a*A + a*B = a*(A+B), then our set is called a 'vector space' and A and B are called vectors. Actually there are about 8 or 9 rules in all for vector spaces. These are the rules of 'linear algebra' and include 'free' vectors in physics such as forces, directions, momenta, accelerations and many more. Mathematically the term vector also includes definite integrals, solutions to many kinds of equations, differential or otherwise, matrices, in fact any mathematical object that obeys the above rule. Tensors also obey this rule so they are a type of vector in this sense. Linear algebra or linear analysis is all about this type of mathematical behaviour. Hence my reference to Kreider This terminology has one unfortunate aspect, however. If we consider the straight line y=mx+C, this is a straight line, but it is not 'linear' in the above sense. The addition of the constant causes a problem that introduces a new type of mathematics we call 'affine' Now here is where the physicists view of a vector as a simple type of tensor comes into play. There are 'constant' tensors we can add to copy the affine structure of the straight line. But there are no constant 'vectors' in physics available for this. I'm sorry if this was a bit rambling but it was rather dashed off to get something down whilst you were online.