studiot

I was taught that (conventional chemical wisdom is ) that hydrogen is particularly dangerous because. 1) It is a very small molecule and therefore difficult to contain, most especially in old perhaps poorly maintained equipment. Leaks are more likely than with say propane. 2) If there is a leak, which there is when you change a propane bottle and can often be smelled around caravans, hydrogen is more dangerous because of its more explosive nature. What might happen if you changed over a hydrogen bottle in the same way ? What about the energy released is it not also greater with hydrogen ? Hydrogen releases 142 MJ /kg compared with your other fuels, gasoline, natural gas, methane etc are all in the 40 - 55 range so hydrogen is nearly 3 times as energetic. Solid fuels come in even lower with wood at 15 -20, coal at 20 -30. Alcohols are also in the 20 -30 range. All I am saying is that the use of hydrogen presents greater dangers than ordinary people are used to with the fuels, containment vessels and technology they already have. Perhaps fuel cells, being liquid/ionic phase will be safer but there is still the issue af a tank of a substance that is very dangerous if it gets out. I am not saying we should not avail ourselves of the technology, just that people cut corners (nuclear technology history confirms this as did London's largest ever explosion which was in a TNT factory). We should always take and enforce extra care with extra dangerous technology.

+1 But more than that, it is a dangerous storage medium compared to some others. However perhaps fuel cells are a way forward. (one day).

I have started a new thread for this as it raises an important interesting question that is not really 'Science News' Suppose beecee's dream is realised and one government or several governments research and develop really good hydrogen technology. Who benefits ? Big business ? The people ?

Yes, indeed there have: one of my more distant relatives was the fire officier in charge of dealing with the Buntsfield disaster. However I looked back to a time when gas that came through the pipe to consumers contained hydrogen gas because:- The changeover to pure hydrocarbon mixtures (mostly methane) started in 1960. And there have been significant disasters with this updated gas as well, for instance Ronan Point . I worked (a very little bit) on the aftermath at what was then called the Building Research Station.

Perhaps you have a short memory. Here are a couple quickly found https://en.wikipedia.org/wiki/Pittsburgh_gasometer_explosion https://www.scmp.com/magazines/post-magazine/short-reads/article/3008553/sudden-and-terrifying-explosion-claimed-40

The use of hydrogen as an energy source is as old as the hills. The use of hydrogen as an energy source commenced in 1792 when William Murdoch lit his house and office in Redruth, Cornwall from town gas, which is a mixture of hydrogen carbon monoxide and carbon dioxide. Since that time the have been sundry vaiations on that formula with 'water gas', 'producer gas' and other combustible formulations. History has also taught us of the dangers of these mixtures, both from poisoning and explosion. A different compound, hydrazine is also available and only marginally less dangerous. In case it is proposed that such materials be confined to industry, there have been many unintentional disasters in industry - industrial scale disasters, of course.

I disagree. I agree. The difference is, of course, that fly by wire is only a small part of the system necessary to fly remotely. Remote telemetry is still very complicated, and all that gear would need to be added to a simple fly by wire air or space craft. And then there is the time lag which becomes ever more significant with distance.

There are several ways to handle catenaries, but I often find that splitting the vertical axis into two with one section constant and the other parallel to the horizontala axis, as in the following.

So is there a problem making the substitution ? You have nearly done the question.

A very insightful comment, without any need to refer to index notation. +1

Why is this not in Homework ? Hints What is s ? What is velocity in terms of s? What is acceleration in terms of velocity ?

The problem with the rubber sheet is that the curvature of a rubber sheet is of the wrong sort of curvature. There are two sorts of curvature, extrinsic and intrinsic. The curvature of the manifold in GR is intrinsic. The curvature of the rubber sheet (manifold) is extrinsic. A further comment is that a single point has no curvature. A line has no intrinsic curvature but may have zero extrinsic cirvature or some value of extrinsic curvature. A surface can have no curvature, both extrinsic and intrinsic curvature or just extrinsic or intrinsic curvature. These situations can all be drawn or sculpted in our 3D world. Once we move to 3D however we cannot draw or sculpt extrinsic curvature and it is very difficult to imagine.

Stromatolites. Amongst the first living organisms on earth circa 3.5 billion years ago and still going today. They were responsible for releasing the oxygen into a toxic (to us) atmousphere and making it breathable for oxygen breathers. https://www.bushheritage.org.au/species/stromatolites https://en.wikipedia.org/wiki/Stromatolite You may have seen the BBC series The Power of the Planet, presented by Iain Stewart https://www.bbc.co.uk/programmes/p00gczg5 An interesting reverse (geological not biological) process is the 'rusting of the rocks' https://www.newswise.com/articles/how-rocks-rusted-on-earth-and-turned-red

Really ? What is n ? That leaves me still waiting for some unit free constant that couples length to any one of the other independent physical dimensions I have mentioned. Do you know what they are? If not are you not curious about my symbols ? I certainly don't agree that all forms of 'Energy' in general are proportional to temperature.

Hi Markus, I know we are always stressing there is no fabric. Have you heard of the cosmic Fabric model of gravity ? https://www.google.co.uk/url?sa=t&rct=j&q=&esrc=s&source=web&cd=&cad=rja&uact=8&ved=2ahUKEwjM-ouXq4PzAhUKxRQKHfQwDd4QFnoECAIQAQ&url=https%3A%2F%2Fwww.worldscientific.com%2Fdoi%2F10.1142%2FS0218271819500962&usg=AOvVaw3Kqo9MvdIjk3xvl4NsgsTR

+1 to Markus for his patient conversation and explanations to Conscious Energy.

Sounds like you are already doing lots of good things for her. Hopefully you realise she will not see DNA with the sort of microscope you are talking about - That sort probably costs more than your house. Thnking and asking about abstract things she can't see at age 6. Wow. May I also suggest some horizon broadening ? Cooking with mummy helps learn how to handle materials. I don't know where you live but perhaps you could take her to a Science Centre, there are some really good ones in Europe (including the UK). Also try to link to things you can see such as plants, animals and the world around her. The changing seasons. some fresh air. Maybe visit a farm. Tell here the world is one big laboratory. But don't get to heavy. That's my advice for starters.

I'm sure you understand the point. My examples are just that. Let us just suppose that every Scot applied to do Higher Pictish Studies and the Scottish Government funded this. Where would Scotland get its future teachers, doctors, engineers, lawyers, and so on from ? And who would employ all the those with a Batchelors or Masters of Pictishness ?

Should higher education be free (a la European) ? Well no one seems to care what constitutes higher education but I see that the expected lines have been drawn so let me ask the question in thelight of the following hypothetical situation. Higher Education in Scotland is free to Scots. (not hypothetical). Suppose everyone only wanted to study higher Pictish studies. Should that also be free ? or If you prefer to consider the point of my question. Should all higher studies be free and how do we persuade folks to take up other more useful studies?

Just a short answer is needed to start with, not an entire exposition of Physics. If I can understand and agree with it I can then follow all your other long posts that have taken so much effort. As a matter of interest the MLT system is not unique, nor is it specifically SI, although yes Système International d'Unités has adopted it. But there are also other systems in use for instance one with mass replaced by force - the FLT system. The FLT system finds favour in Fluid Mechanics as it make this system easier (at least for Fluid Mechanics) as can be seen from this small table. (after Olson : Engineering Fluid Mechanics) Note at the bottom of the table the comment about temperature. I did ask and you have not said how your L system handles temperature.

What do you mean by 'higher education' ? Does hairdressing for instance count ?

Since I asked for a clear example it is only fair that I give you one showing what i mean. On a per unit basis, the molecular weight of water is 18. Superficially, that apppears to be a pure number. But that is because the the real dimensions are hidden in the per unit, which is a gramme-molecule. So a complete statement is the molecular weight of water is 18 grammes per gramme-molecule. The interesting part of this story is that the full dimensional statement is MN, although the N is usually 'understood' and not stated explicitly.

70 posts, some of them have involved a lot of work and I still don't understand the basis of what you are saying about dimensions. Most of what you have posted assumes the reader understands and agrees with your basic statement about dimensions. I don't understand or agree. You mention unit analysis and also Tesla. There is a form of analysis in electrical power engineering called 'per unit' analysis. I don't know if you are trying to emulate this. The problem with 'unit analysis' is that the dimensions are hidden in the 'units' employed. They haven't really gone away. So can I respectfully suggest you put some of this effort into developing (proving) your underlying claim once and for all? Perhaps showing one simple example developed from start to fininsh, but involving as many as possible of the seven basic quantities in the LMTAθIN system. For your information here are two free websites where you build mathematical formulae and copy/paste into ScienceForums. http://www.sciweavers.org/free-online-latex-equation-editor https://www.codecogs.com/latex/eqneditor.php

Yes of course the business of Physics is to examine the interactions of its laws and the resulting structures in excruciatingly fine detail, as well as discovering and enunciating the laws themselves. But my point is that it is not the laws that can be scale dependent but the results of their interactions. Some are some are equally definitely not and some vary as scale varies. I gave some examples, but I am surprised considering one I have not mentioned, that cosmologists do not accept this since the spectra resulting from electron transitions and molecular vibrations are held to be that same at either end of the universe as on Earth. How's that for scale ? I do agree with your comment abour Reg/Davy/...? although it would have been nice if he knew when to call time on antics.

No I don't think you did answer either my questions, nor those of swansont. Anyway the OP picture 1 is purely Newtonian. GR is not involved. The curvatature is in the values of Newtonian gravitational potential. It is a depiction of a Newtonian gravity well. There is a similar picture of the Schwarzchild solution in GR which with which it should not be confused. @pmourad This New Zealand teaching website offers a really good explanation and some interesting material to play with. https://www.sciencelearn.org.nz/image_maps/76-exploring-physics-concepts-with-a-gravity-well