studiot

Depends what you mean by a vacuum. If you mean a complete void - empty space with nothing in it, not even air the no there isn't. But if you adopt a polular (also scientific) notion as being any region where the gas pressure is below atmouspheric then yes. This is often called a partial vacuum and can be measured as so many milliletres or inches of mercury below atmouspheric pressure. As a sports scientist I hope you realise that the old phrase Nature abhors a vacuum is nonsense. Most of the Universe is empty space. Your lungs do not suck air into them when you breathe in. The outside air pressure pushes air in when you expand your lungs by lowering the diaphragm. This lowers the air pressure within your lungs to below atmouspheric. There is no such thing as suction.

Well put. +1

I believe I did.

Markus has mentioned 'projections' several times recently. It is worth noting that there is a difference between a projection (called resolved parts in my attachment) and a component. Unfortunately distinction is blurred for many because they are the same thing in orthogonal coordinates, but become different in other geometries and the use of tensors. This arises because of interaction between the variables in non orthoganal systems.

Like all your posts I have read all your answers and responded directly to them. What you have written here is just plain rubbish You cannot slow a light wave, or any part of it. Electrical planes, whatever they are, do not travel through anything. Yes, elementary polarisation phenomena have been known since antiquity. But the important point, as I already said, was that knowledge at the time of Fresnel and Arago was insufficient to explain polarisation. I never said they did. Here is your quote from Wiki again. All this stuff is based on assumptions there is no need to make. And all the history of the development of our understanding of the phenomenon we call 'light' bears this out. We have been through several cycles of 1) We have observed some usually common characteristic or property and hypothesised explanations/mechanisms for these properties within existing knowledge and theory. 2) Someone then discovers isolated incidents where light behaves differently in some way. 3) We are then faced with extending our theory or even radically revising it. 4) But light still continues to follow the previous set of behaviours so continues to act in that way if called upon to do so. 5) And we do not need to abandon the earlier models if they are satisfactory and easier to calculate for the circumstances they were originally conceived. So, for instance we still use rays in geometric optics for most work. So this brings us to the Wiki statements which try to force us to make either-or choices about our hypotheses. There is no need to invoke rewriting the past or make a wave/particle choice if we simply say that light is a complicated phenomenon which has the capability to interact in composite-like, component-separable-like, flow-like, particle-like, ray-like, wave-like and now sometimes some other manner yet to be fully understood. In fact it is so complicated that I have probably missed some important behaviours off my list. You have indeed answered at least one of the many questions I asked, but you have not addressed all of the points in any of my post. This is regretable since all my points have been either directly aimed at answering or discussing a point you had previously made or adding something I considered germaine to that discussion. Since you clearly do not consider any of these of value I will leave it at that.

A shield can be as simple as a fixed deflector plate. I mentioned at least twice that it is structural support considerations that limit the size of vertical axis rotors. Perhaps you should follow the new thread on bending moments in Homework Help.

The signs you calculate will depend upon your sign conventions. If you are taking the dowward loads as positive then reactions will be negative. I can't deduce any more without you posting your working.

Jus to add to swansont's answer. @bangstromWhy do you not answer my questions ? Fresnel - Arago's work was between 1800 and about 1817. At this time interference and diffraction were known and partly studied phenomena. This was enough to lead to a simple scalar wave theory, but not enough to explain polarisation, which was known but less well understood. Basically results were all empirical at that time. An explanation of polarisation and its actions did not arrive until Maxwell published his vector theory of light in 1865. As swansont says, this was based on the vector electric field being the leading actor. It should be noted that this is not the vector associated with the scalar wave theory of Huygens. The electric field can be plane polarised (do you understand what this means - please answer this time). Since in 3 dimensions two planes can exist at right angles and a vector in one plane has zero component at right angles to its own plane and therefore cannot affect a vector in the other plane at right angles, Two such vectors cannot interfere. I was going to draw some diagrams to show how this polarisation works and how it can lead to circular polarisation but you may have seen such diagrams ? Polarisation is therefore a good way to obtain light as a plane wave, as needed for the slits experiment.

I gave you the Physics, what problem do you have with it and why have you not taken on board what I have said several times about diameter ? Yes, but you can shield against this effect, which you would need to do anyway as you do not want the rotor to be driven backwards in certain winds. In a wall such as this vertical axis rotors loose their principal advantage that their operation is independent of wind direction. In the extreme they would not work at all with a wind blowing parallel to the wall. So like all systems they concept has attractions and drawbacks which must be balanced against each other. I'm trying to be even handed here and keep an open mind.

You mean you did not understand what I offered you so you chose to insult me rather than ask for better detail. Should I report this as an infringement of the rules here?

This has no meaning in (special) relativity. All motion is 'relative', and you have not specified this part. Such a distinction is not necessary for light itself as it has the same speed relative to all bodies. But this is the only case where this happens. Even zero speed is relative to something. Really ? How Again this statement is woefully short on detail. Where did the 'block universe' creep into your theory of relativity ? I will grant you the aliens bit with the proviso that what you are describing is what said aliens could calculate if they existed. Of course they do not, but with suitable maths (do you have any ?) the appropriate relationships can be modelled and calculated. But again the calculations have to be done in somebody's terms and again your have left the issue of whose terms unaddressed in your question. Not 'exactly'. Again I'm looking for some maths here, not belief. Ask (less than) half a question and you are getting more than half an answer since I am pointing to what needs to be done to complete your question or statement.

I'm sorry for that misunderstanding. Please substitute the impersonal 'one' for 'you'. I am also aware that appearances can be deceptive and that images in mirrors are virtual and so on. But all of that is a digression form, the emission of one single photon and how or if that might be described as a plane wave over the entire approach space to the slit wall. The OP keeps mixing up what happens with many photons (ie a full wave) and a single photon, and keeps introducing esoteric experiments that only occur under highly specialized conditions not as special cases, but as general theory. Further the OP says he favours the wave theory but does not seem able to correctly describe the wave or what usually actually happens so I have been trying to start at the simplest and build up to more complicated effects one change at a time.

I didn't say you did. The model was proposed (and dismissed) by the OP, then reintroduced by the OP in the form of a quote from a Wiki article. Do photons not originate at a photon source? Can they actually originate anywhere else ? I repeat a slit is not a photon source. If it were you could remove any other photon source from the experiment. I also note that most sources have some form of conditioning device(s) to focus or spread or otherwise produce the desired light distribution pattern. Which is consistent with the wave model, not the photon model and does indeed make the space between the slit walls into new sources. But it does not say that photons constantly disappear and reappear as new photons as the light progresses. But I'm sure you know all this.

Apart from fan heaters designed by marketing departments just so they can offer something differenct, most are of the of the cylindical type. Mount a series of these one one top of the other with their axes vertical if you must and you have a ready made wall of generators that does not disturb the airflow in the way an airofoild blase does. Aerofoils produce jets, which involve turbulence. The energy of turbulence air is not avialable for extraction. If mounted one behing the other in the airstream obviously the each succeeding genertor, however it is mounted, will suffer reduced performance relative to its predecessor since the predecessor reduces the wind speed somewhat. That is where the energy comes from. It is recovery from this reduction of windspeed that requires the spacing of the turbines. As I understand the proposal the 'turbines' are of the vertical axis cylinder type, mounted one deep in the wall so this effect will not be evident. The main reason for the lower efficiency of vertical axis machines is that the diameter that can be supported is limited substantially compared to horizontal axis machines. And it is the diameter of the tip that determines the maximum speed and therefore output. I have already mentioned this in a previous post.

When I said everything I included the source. If you are going to propose a model where photon 'bullets' are fired through the slots then you have to demonstrate the complete path from start of the bullet to impact with the detector. The Wiki article was just poorly worded. The objectional word is originate, not appear or 'behaves as if'. WE all do it and bangstrom has already pointed out that my textbook has also done it in talking about polarisation. However with smart alec way every response is being presented, I don't feel inclined to continue developing the discussion further.

Perhaps you should revise your aerodynamic theory ? With laminar flow there is no interference between the units. A lot of smaller units have the advantage over one big one in the event of a unit breaking down / needing servicing electricity supply is hardly interrupted. One big one is an 'all your eggs in one basket' situation.

I don't agree. If that were the case then you could remove everything before the slit barrier and 'photons' would still 'originate' from the slits.

You don't seriously expect me to continue our conversation, following that reply do you ?

Wiki is not always accurate. Photons do not 'originate' from slits.

No thanks for several offers of help then with your editing problem. Goodbye and close the door on your way out.

I also meant to say that phase is one of the important basic characteristics of all waves, shape is another and strength is a third. Simple plane waves have the characteristic of not loosing strength they propagate because they don't spread out.

BLANK well who'd have thought that. Drag and drop works. But fine control (positioning within 3 lines) is impossible.

I will try that, I have never found a way to move down the top quote short of using cut, followed by typing something in, followed by pasting the quote back in below the new typing.

70 something posts into this thread an it sounds like you are actually asking a question, instead of laying down incorrect law. Progress. So you have been told that light is a transverse wave (swansont again). The point of using planar waves in the models is that they don't spread out. They are particularly simple to work with because the three dimensions can be separated mathematically. All segments of the wavefront have the same direction of propagation, and all the oscillatory action take place in planes that the line of direction is normal to. Each plane is a plane of constant phase. A

No one is being silly. My heat pump vanes can quite easily ice up when there is no snow or ice about, due to quite low speed air movements through them. Microgeneration. Yes, that is why the diameter of these huge wind tubine rotors is so large. I wonder how thick the 'wall' need to be to generate any electricity from any reasonable wind speed, after overcoming friction of course.