studiot

yahya, Did you miss post#4 or are only certain members allowed to comment?

Tylers, This is all getting very complicated. One simple distinction you should know is the difference between atoms and molecules. All atoms are molecules. But not all molecules are atoms. Molecules are the smallest unit of any substance (ie matter). The definition of any pure substance is that all the molecules are the same. Some molecules can be broken down further but the results are not the original substance but atoms. Atoms are molecules of special substances, known as elements. These cannot still be broken down further and remain as matter. All molecules are made of slightly less than 150 known elements. Some elements exist in normal conditions as multiple atoms of the same element forming molecules. Examples are oxygen and hydrogen. A combination of oxygen and hydrogen exists as the water molecule. Helium normally exists molecules comprising a single atom. Hope this helps.

I think you misunderstand the nature of centripetal force. Centripetal force is a real force that has to be applied to a body travelling in a curve, by an external agent, if we can consider that body to be a point particle. Gravity is one such external agent and the gravitational force is centripetal in nature. A point particle means that all the mass of the body can be considered to act as though it was concentrated at one point. Centripetal forces act within a body turning on an axis, but not on the body as a whole. These forces act between the individual particle or parts of the body and are usually manifest as a variation in the cohesive forces holding the body together. There is a further complication in that the centripetal force at any point in the trajectory (which may not be a circle), is directed towards the centre of a circle, which has a common tangent to the trajectory curve at the point of interest. In general, when the trajectory is not a circle, this centre point will vary in position and the distance between the common tangent point and the centre (known as the radius of curvature) will vary. In order to account for this it is usual to work in terms of acceleration, not force, and call this centre the 'instantaneous centre of acceleration'. Working in this way you can add the accelerations (vectorially) on any part of an orbiting planet to generate the true path of that particle on the planet. The accelerations are, as you say, separately due to the centripetal effect of gravity acting on the planet as a whole combined with the internal accelerations due to spin, wobble and other movements, including variation of linear speed. Very tricky indeed.

+1 for fairness and astuteness. With all due respect I would see this as a political statement rather than a scientific one.

I like levity +1, sunshaker.

How about this famous one http://en.wikipedia.org/wiki/Growth_in_a_Time_of_Debt

+1 Never seen one of these, thanks.

Again I am currently short of time but you are missing part of the equation [math]{\bf{B}} = {\mu _0}{\bf{H}} + {\mu _0}{\bf{M}} = {\mu _0}\left( {1 + \frac{M}{H}} \right){\bf{H}} = {\mu _0}\left( {1 + {\chi _m}} \right){\bf{H}}[/math] Look up susceptibility.

Swansont If the filings were free to move, sure. That's what happens when you put ferromagnetic material near a magnet — they attract. But the point of filings on paper is that there's friction and the filings won't necessarily move closer, regardless of "wanting" to. You just get alignment with the local field. It doesn't work like that, watch the movie carefully. Again I say remember it is a complicated 3D effect, which is why many teachers avoid it.

Fair question but think about a balance of competing forces. Remember also that the magnetism in the filings is induced, not permanent. I was trying to show that there is a net balance of forces on the particles from repulsion from those on either side in 2D and above/below in 3D. I meant to add these into my sketch this morning but, I am dealing with two domestic emergencies (a result of crappy electrical design) at this moment. One in the fans of my fan ovens in the cooker and the other in the mains input filter to the washing machine. Why can't modern manufacturers make things last for more than a year?

Because the nearest end of any particle to the bar magnet will be of the opposite pole! This is as I tried to show in my sketch. So the end of the first particle adjacent to the north pole of the bar will be a south pole and so on. Here is an expanded sketch of the north end of the magnet showing what I mean. Did you notice that the second video on the iron filings said that it is a three dimensional effect (which you can see if you look carefully). We are only drawing two dimensional sections through this.

This is the difficulty in comparing the field distribution in a medium that can be physically moved by the field and one that can't. If you had a small enough compass you could use the following method to see that there is next to no field between the chains of filings. https://www.youtube.com/watch?v=JUZC679CwKs Without the filings the field pervades all space and anywhere the girls starts her point you can trace a line. But usually this is not discussed when filings are used to show the shape of the plot. https://www.youtube.com/watch?v=j8XNHlV6Qxg

Not really, no, but we gloss over that for elementary demonstrations. A flat steel sheet would be closer to the air/free space distribution, although more tightly 'pulled in' to the bar magnet. The 'shape' remains the same, but the distribution of the lines changes. Remember for free space or a flat sheet the lines can't interact since the tiny magnets are fixed in space. But the use of filings allows the lines to interact, although it exhibits the same onion shape from the bar.

Here is a very rough quick sketch, from which I hope you will catch the drift.

Good observation +1 As imatfaal says the iron particles line up so they are touching as continuous chains of tine induced magnets. Why? Well this is a good example of a system seeking to minimise its energy. Without the filings the magnetic lines are 'evenly' distributed in space with no gaps. Even is not exactly right since obviously the field strength diminishes with distance from the pole to pole centreline, but I think you know what I mean. Just as with a transformer or motor core, the field lines (want to) congregate in a ferrous material ie they are drawn into it, leaving few lines in the free space not occupied by the ferrous material. But these paths have to be continuous through the core. Cores are not free to move, fine particles are. So the system can rearrange itself when fine particles are introduced. And yes, indeed there are few lines in the spaces and a concentration of lines in the chains of ferrous particles. If you were to plot some lines at right angles to the chains you would find repulsive (N-N and S-S) forces in action, which is why you get spread out lines rather than a block in the middle.

As a start reluctance motors fall into two types. The first type employes some form of permanent magnet. The second type has its poles magnetised by induction. Of this second type synchronous reluctance motors (eg old fashioned electric clocks) are run up to speed unmagnetised and then the poles are magnetised.

Chemically, solutions are best fresh and not stored for long periods. But fresh is a relative term, which depends upon the stabiltiy of the compunds in solution and their reaction with things light light. I do not think you have any such problems here. So I would suggest you could easily mix up a week's worth at a time. Mixing is not difficult, just churn the powders in, to the cold water.Heat should be unnecessary. The only safety issues would be to avoid breathing dust (face mask if powder is fine). I do not know the quantities involved, or the source of your water. Neutralisation is an interesting point. Natural aquifer water may be slightly alkaline or acid depending upon the source rocks, but soilwater is usually acid. I understand from horticulturalists that flowers like more acid water than vegetables, as plants, but know nothing of cut flowers' requirements. Suspended organic material may grow in the sugar solution.

I'm sorry you have taken umbrage with my post. It was not meant to be mocking, perhaps you might like to consider the old adage Act in haste, repent at leisure. Not only did John Cuthber originally try to help your balancing efforts, but he also tried to calm less temperate comments. He also told you exactly what was wrong with your balance and what needs to be done to correct this. Though his replies are often very concise. Actually a compliment, this is not basic or elementary chemistry. But balancing a chemical equation is basic. Since John had already told you how, I took the trouble to find a reference to a similar if not identical reaction (your original desciption was not entirely clear) to help further.

I have never found any benefit from the 'Friends' system in any forum that I have been involved with. Such systems seem to be mandated by the annoyance division of the 'Forum Software Writers Association' and comes with all forum software. I avoid any involvement in forum 'Friends' processes. The reputation system has merits, however. Personally I have only issued negative points twice (I think) in the three years I have been a member here. Certainly I condemn the practice of piling on the red as Ant Sinclair reported here. Surely if someone has done something annoying, 1 red mark is enough to make the point? I use the green points less sparingly to encourage what I consider good practice or to express admiration for a point well put or well argued. I also agree with the OP that if something is worth making a note about, good or bad, it is worth stating that note.

Sucrose is ordinary white sugar, so no problem there. Both Aluminium suphate and calcium nitrate include what is known as 'water of crystallisation', when in crystal form. The aluminium sulphate has 18 molecules of water per molecule of supphate and the calcium nitrate 4 molecules per molecule of nitrate. The weight of this water (if present) must be taken into consideration when weighing out for solution. The good news is that both are highly soluble (not too many calcium compounds are) and non toxic. Calcium nitrate occurs naturally in soil and is also manufactured for use in fertiliser, Aluminium sulphate is used as a scavenger to 'clarify' water another form - alum can also be used. So the first and most important question is for you to find out what form your salts are in. Are they without the water of crystallisation (the called the anhydride form) or Are they crystalline?

How does that play with financial experts advice and their stock disclaimer "past performance is no guide to future gains or losses"

There have been many examples of deaths around the world due to the dogmatic approach offered by posters here. In general the dogmatic approach has, IMHO, more to do with apportioning blame and ass covering than achieving satisfactory results. The safety 'expert' says there should be fire exits. The security 'expert' says all doors should be locked. Result? Tragedy. Experts can disagree. What then One expert's 'solution' may be excessively costly or onerous. One 'expert' may tell you that margarine is better for you than butter. Another may tell you the opposite. What then?

EdEarl +1 Or the set task was impossible in the first place. Incidentally I did not specify an absolute 'expert', just someone more so than the promoter. Of course the 'no discussion' approach precludes the expert offering that there may be another (better) way that the 'manager' has not heard of. Or how about this scenario. We wanted a new shrub to go in a particular dry sunny corner of the garden. We settled on a hydrangea. I am really glad we discussed this with the nurseryman as we have never heard of the variety he came up with, but it has certainly thrived there. He also said that most of the more standard varieties we had heard of would struggle in that location.

John Cuthber In principle, no. Of course the level of discussion depends on how much you know about their field of expertise. If there's anything you need to discuss, it's because you didn't specify what you wanted properly. And, if they are the expert, what's the point of the discussion? You are just going to end up agreeing with them because they are the ones who know what they are talking about My experience has been that approach soon leads to spectacular failure.

No it is not OK, but no that is not because it's not an admissions policy. I think imatfaal's point is that in order to come under the ambit of the referred Act, there must be an admissions selections procedure. SF has no recognisable and identifiable selections policy or procedure, therfore does not fall within the ambit of the Act. However that does not relieve SF of complying with all other relevent Acts in its subsequent dealings with members, including dismissal. I do believe there are many other Acts, or even parts of the Act in question, concerning discrimination. It is very common for people to think that because one Act has granted a permission, all other duties to comply with other Acts are abrogated. I can remember constantly explaining to people that, whilst, yes they have successfully been granted Planning Permission to have a driveway, the implementation of that driveway must still be in accordance with the Highways Act and that said Highways Act contains a secon permissions process of its own.