studiot

OK so here is my critique of the video. Firstly this question is not a high shool question it is university level. But at whom is the video aimed ? Well at the end he talks about the "Physics coolkids club", implying an intended school level audience. Yes I'm sure he knows and many of my comments would be quickly picked up by un undergraduate physics class. So he starts by introducing the index of refraction, as a measurement of the observerved slowdown, but then only uses that index for a flashy optical illusion that I rather like, though I question its worth in the explanation. He states, without support that the index is a measure of the slowdown. Then at 3 minutes in he says there are two completely wrong explanations going the rounds but does not say that both effects are actually observed fact, although, as he rightly says, they do not contribute to the slowdown. A junior audience might be forgiven for believing that neither scattering nor absorbtion actually occur. In dismissing both these explanations he uses both good animations with spreading or fuzzy light rays, and poor ones looking like 1950s atromic representations. In particular he shows both scattering and absorption by the nucleus only an fails to distinguish between the nucleus (red dots) and the whole atom. What makes it worse is that he lated describes glass as made of atoms surrounded by electrons. How's that for confusing the coolkids club ? Then he correctly introduces his explanation as a wave explanation and again correctly shows how two waves of different velocities can be combined to form a new wave of slower velocity than either of them. But in his explanation both his waves are going in the same direction. He ignores the fact that the electrons (which actually produce the random scattering not the nucleus) will be travelling every which way but loose ands so any wave their interaction produces will be just as randomly oriented. He also says that light is just oscillating electric fields, again suggesting to less experienced minds that there is no magnetism involved. At around 8.00 he correctly says that electrons experience a force from an oscillating electric field and move under the influence of this force, in turn generating their own electric field its their own new wave. But he does not say why this new wave has a different velocity from the driving field, which was his condition for the resultant being slower. At 6.37 he introduces superposition, but does not mention Huygens principle. So all in all I do not feel that this video provides a satisfactory explanation, although it does satisfactorily rules out a couple of others. Since he does say that a new wave is generated, he is marginally better than the others, but also hides missing pieces of his own explanation whiils overcomplicating parts of it.

Smashing. I will try to work with that ans see how we can get to Seth's formula. First I would like to make it absolutely clear that The force on the windward face of the wall depends only on the winf at that face. It does not depend in any way on what happens on the other side of the wall. It may even be that the pressure and force on the other side of the wall is very much greater, for example if the wall is a dam wall. The windard force will be the same whatever happens in all cases. The wind blows horizontally for convenience and I would like to consider a round tube of air in this wind with an area of 1 metre2. The reason for choosing a round tube will become clear. Fig1 shows this tube and fig 2 shows how the airstream in the tube impacts on the wall. OK so the wind is travelling horizontally along this tube with steady speed v until it hits the wall face. Splat. Except that is is a continuous process. So the air must be diverted sideways along the wall face. If this did not happen then there would be a pile up of air at the wall face as more air continued to move along the tube. This is called continuity and we therefore have the equation Volume or mass of air arriving at the wall face = volume or mass of air spreading out along the wall face Now mass arriving per second = volume x density arriving per second = cross sectional area x length of tube arriving per second x density And the length of tube arriving per second is the speed of the air flow (speed = distance/time). And we have set the area of cross section to 1. So we have mass per second = 1 * v * d Where d is the density. You have mentioned that momentum = mass time velocity So the momentum per second = mass per second x velocity = v *d*v = v2d units of momentum. We have also specified a horizontal wind so all the momentum is horizontal. The vertical momentum is zero as is the sideways momentum. But at the wall fact the horizontal speed suddenly bcomes zero so the horizontal momentum suddenly becomes zero. That is all the horizontal momentum is destroyed or lost. Now you may have heard of the principle of conservation of energy ? There is also a principle of conservation of momentum. This says that momentum is also conserved, unless there is a force in which case the force is equal to the change of momentum per second. The change of momentum per second = (v2d - 0) so this equals the force acting on every square metre of wall the wind blows agains. I have tried to show this diagramatically in Figs 2 and 3. This also shows why I have used a circular tube. The vertical and sideways momenta start off as zero and no force acts so they must remain as zero. This happens as you can see in figs 2 an 3 by symmetry there is always a balance of momenta that sums to zero

He does indeed say exactly that and I gave you the time stamp. Although I was wrong in saying I thought he said it twice. Hes also says Glass is made of atoms surrounded by electrons, around about 7.58 But as G & S say "I've got a little list" It's coming, but I'm trying to reply to our newbie's question about wind forces first so it will be later today.

No one is laughing at you. You have some good thoughts. One definition of a dimension is "the number of independent pieces of information (co ordinates) you need to specify the position of a point. So you need for instance one distance from 1 point in 1 dimension, two distances from two points in two dimensions, 3 distances from three points in 3 dimensions and 4 distances from 4 points in 4 dimensions. But eyes are not points, as Genady says they have visual overlap - they are two dimensional patches. This is how the brain can get the extra information requires to measure in 3 dimensions. Again but as swansont says, 4 dimensions introduces extra complications so more detail is necessary.

Good morning, Rocks and welcome. Yes the wind speed may be constant and force does indeed equal mass times acceleration. But whilst speed is a scalar it is not the same as velocity, which is a vector as is force and acceleration. So the equation Force = mass x acceleration is a vector equation. I hope you know that vectors have both magnitude (the scalar part) and direction and that these two quantities can change indpendently of one and other. So the acceleration (at the wall) is not zero because there is a change of direction. To see how this works you need to consider yet another vector quantity called momentum, which undergoes significant magnitude change at the wall. The force arises as Newton has another equation Force = rate of change of momentum. Please let us know where you are studying momentum so we can finish off an appropriate reply, to show you how to calculate the force from the speed and mass of the wind. The other replies are true, but their effects are not really relevent to your question.

So far as I can tell no one here thinks you are a flat earther and noone has been mean to you, their replies seem to me to be quite helpful. I only introduced flat earth because actual flat patches on a planet's surface can and do occur and have geological significance, indeed there are several terms in geology reflecting this. Peneplain, plain, planation etc. I'm sorry if my comments confused you. However your discussion so far seems very nebulous so that I am unclear about where it is meant to be heading. What do you actually hope to do with the information ?

Thanks +1

Thanks for your input. +1. I thought he has stated that twice, but even once is not good when you are dissing other people, especially as the video was not properly checked (ie hurried). I will come back with my full list but, He seems to imply that photon scattering only happens off the nucleus. In fact My highlighting.

I'm glad to see you are working at least some of this out for yourself. So much more satisfying that way. Here are a couple of practical facts or 'rules of thumb' for you. Cartographers and surveyors work in the '10k flat earth principle.' That is, you can treat the earth as flat and the grid as rectangular, and trigonometric calculations as plane trigonometry within a region about 10 kilometres across. Talking of flat earth we had a flat earth nutcase here who was trying to prove the earth is flat by surveying Lake Balaton in Hungary. He did not succeed, but the discussion did uncover some interesting geological facts about the alke Baloton region and also more generally, because glaciers creat flat bottomed valleys.

Robert Mills ( of Yang-Mills fame) writes very persuasively about this and many other things in his first year university level book. He has a very clear way of putting many concepts.

Nice pictures. Can I respectfully suggest you do some thinking for yourself here. You should be quite capable of ansering these questions yourself. First just check up on the difference between a level surface and a flat surface.

https://www.bbc.co.uk/news/science-environment-64603521

100,000 feet up is 19 miles up ? Edit Xposted with swansont.

iNow already answered that Although the US has watched such incursions before, I further suggest this time presents new information because of Ukraine. China and Russia have become very pally recently.

Take a pen and paper and note them down as you go through. I noted several: we can compare notes when you have done.

Did you notice any faults ? Perhaps the one at 5:34 where the Dr Lincoln says that "Photons absorb atoms"

If Lincoln genuinely said that then the video is best forgotten. Now to horse to horse. @Boltzmannbrain I am going to offer you a wave explanation, though the principles that come out of it apply to any level, including quantum. So first what is a travelling wave ? A wave is described by an equation connecting time and space. In order to make this equation dimensionally corrrect (all terms in the same units) it must include a factor we call the velocity or speed. The basic equation is a differential equation which is satisfied by an infinity of ordinary equations , also called wave equations. All these equations must include the units factor I mentioned. These waves have certain charracteristics or requirements. Before a wave can travel it must be generated. Seems obvious, but the equations themselves do not tell us how this is achieved. The velocity of a wave is characteristic of the medium, not the wave. If a wave has material moving elements or particles the speed of these is not the same as the speed of the wave. In the light of 2 it is not suprising that a wave travels at different speed in different media. So let us consider a sound travelling through several media, air then a solid partition (say a pane of glass or sheet of wood), then back to air again. Very simple but it will do the job. In the air the sound wave is made by the particles alternately bunching together (thus increasing the pressure and density locally) and spreading apart (thus decreasing the pressure and density locally). Note that these air particles are free to move about. They are not linked to other particles directly by forces. When the wave arrives at the left hand partition surface this alternating pressure increase and decrease causes alternating displacements of the surface particles. Note these partition particles are connected to neighbouring particles by springlike forces as in my original diagrams. This pattern of alternating displacements is thus transmitted onwards through the partition to its right hand surface, where the reverse occurs and the motion is returned to the air the other side. Now these two modes of tranmission are fundamentally different by virtues of their different mechanisms. But there is only ever one sound wave in either medium. This process can be likened to handing on the baton in a relay, each runner operating in a manner appropriate to him or her. The baton is the wave energy. A travelling wave transmits energy and the mechanism of travel will, unsuprisingly, vary from medium to medium. So sound is not light, but they are both waves. The mechanisms are different but the above applies. That brings us to the level of mechanism you wish to study the phenomenon for light ?

The op claims to be new Has anyone else the feeling of deja vu ? I'm sure i've seen this junk before and I can't thik where else I might have seen it. Does anyone else remember such a post ?

Yes I too like least action but by itself that does not provide the mechanism. +1 Your 'lattice field energy' appears in a simpler guise which I explore below. I rarely try to explain the videos of others, and like joigus I didn't watch this one. But I try to relate your idea of forced oscillation to Seth's lattice field below. This too is a good one, so long as you are not trying to imply that there are two waves transmitted in the medium travelling at different speeds. +1 also Yes I agree it is difficult to provide a simple intuitive explanation but I think I can now offer one using my sound analogy as below. You can also classically make this as complicated as you wish. Joos (Theoretical Physics) takes four chapters to develop it from simple vector calculus to tensor calculus for the anisotropic case where ε is a tensor complete with components and principal direction, dependent upon position in the non-homogenous case. My first pages above were from The 1966 MIT series "The Structure and Properties of Material - volume IV - Electronic Properties" byRose, Shepard and Wulff The second pages were from Vibrations and Waves in Physics by Iain G Main Cambridge University Press. (My copy 1979)

Sorry for the spellung mistake. No offence meant. I had in mind "possibly the Forest of Dean" but never mind the other side ok. The last time I visited the Stonehouse asrea I had little or no signalin and around Hetti Peglar's Tump or around the Cotswold edge below the momument. Indeed the edge country Broadway right the way down to Thornbury is littered with mobile blind spots. But thanks for the info.

Doesn't this violate both the first and second laws of this forum ?

Here is a more mathematical classical treatment. Things to take away. Coherence/incoherence v superposition scattering dispersion Real and displacement currents

Not really. exchemist said distorted not combined or speeded up. Read these two extracts.

I'm sorry @Genady I was called away in the middle of responding to joigus, to whom my question "why" was addressed. You seem to have slipped in with a post between posts in our earlier conversation. Anyway I have the time now to explain more so here we go Firstly let us note that gravitational forces (the original question) always draw matter particles together and that sometimes they are aided by other processes (not necessarily forces) as already discussed. Set against this, electric charge can either act to draw particles together or spread them apart, depending upon polarity. Also if a particle is charged it has an excess of one charge over the other. So this excess charge will alway be repulsive with charges of the same polarity. This means that, unlike gravity, charges of the same polarity will never form an accretion process, drawing more and more such particles together. So the question arises "What happens when a neutral body of many particles becomes charged " Well that depends on the shape of that body before it became charged. The girl's hair forms a perfect example of this. The hair does not form a sphere with the charge spread over its surface but forms that spiky shape with repulsive forces on each hair balancing out in some respect. Micelles and other accretion bodies such as chelates in solution work like this. Yet another possibility are the balanced zwitterions. hope this helps

That didn't answer my question. It's a lot more complicated than that