studiot

Asimov's hypothesis eh? Since it takes no energy to exert a force, why would it loose energy to simply be quiescent ?

Would you like to explain your hypothesis in relation to this graph? I have plotted V against a variable I have called time. For a distance along the horizontal axis V is constant (nothing happens) The for a second distance V is exactly zero and so on. So how does this relate to your claim time only exists when something happens, IOW how do you quantify the periods where nothing happens? Also how do you identify clock ticks? What happens between the ticks?

At last a sensible answer to a smarty-pants question. +1 I disagree with this most strongly for the reasons Strange has already outlined, plus the reason I already outlined. A better statement would be We very occasionally measure the distance between two nuclei of two atoms and divide the it by 2. and then outline the conditions under which this statement holds true. For example why are the atomic radii in ethane, ethylene, and acetylene different if measured by this halving the interatomic distance method ? Would you apply the same method to the radii of oxygen and carbon in a carbonyl group, making them equal ? Or perhaps you would suggest that the radii of hydrogen and flourine are equal in hydrogen flouride? But of course none of these atoms are isolated, they are part of a molecule. So do what I said and take a two metre cube of helium gas and take one atom on one side and one on the other. Their interatomic distance is thus two metres. Half that is exactly one metre. So, according your claim, the atomic diameter of helium atoms in helium gas is one metre.

~Consider some helium atoms bouncing around in a container. Each is about as isolated as you can get, but would you measure the (instantaneous) distance between two atoms and divide by two? Which two would you choose?

Well I'm just packing to go to the clinic so I thought a quick response was better than no response. The field ion microscope produces photmicrgraphs of individual atoms (The Wiki article shows the original one) The device is a measuring microscope which means that its version of a microscope graticule has a measuring scale. So we can measure the radii of the atoms. Though the textbook is quite right this is not the same as picking up a golf ball and using calipers. But it also depends upon what is meant by isolate. So I would invite mundane to expand a little on his query.

Do we always do this? And by the way, it is usually Physicists that are interested in the wave functions of atoms, isolated or not. Chemists are more usually concerned with the wave functions of molecules.

You misunderstand me. Where did I say you have to know the state of every (or indeed any) particle ? My point is far more fundamental than that.

Isn't it? https://www.google.co.uk/search?source=hp&ei=UIsdXtz5O8G-adTlpMgP&q=force+ion+microscope&oq=force+ion+microscope&gs_l=psy-ab.3..0i22i30.468.5898..6304...0.0..1.1014.6878.7j0j4j2j2j3j1j1......0....1..gws-wiz.......0i131j0j0i22i10i30j0i13j0i13i5i30j0i8i13i30.iUmCiJDMAVQ&ved=0ahUKEwjc4bH45ILnAhVBXxoKHdQyCfkQ4dUDCAc&uact=5

Thank you for the reply. It is clear that whoever wrote that article you refer to neither understands probability nor predictability and so is leading you up the proverbial path. The giveaway is that it makes numeric predictions without uttering a single number. Yes smoke is unpredictable but not outside the bounds of science. Do you understand the difference between the exact predictability of Boltzman which results nevertheless in a probability and the unpredictability of turbulence which is also treated probabilistically and exactly why this difference occurs? In a word it is due to the existence or not of 'states'. Any by the way you keep asking for equations. There is much more to Mathematics and Science than equations.

I don't know, I have never heard of the Man. but you also said this, which I fully agreed with Alternate periods of Global Warming and Clobal cooling have occurred throughout the Earth's history. It is the natural state of affairs. There have been pretty well no substantial periods of temperature stasis. The point I am making is that pretty well all the energy involved in the surface warming comes from the Sun. There are several factors involved in how much this is. 1) Solar output incident upon Earth's outer atmousphere. 2) The % of this actually reaching the Earth's surface. 3) The % of that reaching the surface that is absorbed and not reflected stright back. 4) The % of radiation from the Earth's surface that is retained due to Cuthber's blanket (which includes CO2) As a matter of interest here is an example of what I was describing leading to cooling in December 2019 smog (item 2 on my list) https://www.bbc.co.uk/news/world-asia-india-50953950 As regards the increase in CO2, the same thing applies. The concentration is multifactorial as it is a dynamical system. We should also consider, for example, the amount of CO2 reduced

That's too simplistic was my point (and also it appears, swansont's)

Before tensors were properly developed there was a half way house between vectors and tensors called dyadics, whose elements were called dyads. This appears to be a similar half way house, a simplification answering some questions but not others.

Good morning Sam and welcome. Was this a class question to think about? The short answer is that very little if any water is lost. Concrete is made from cement, aggregate (largers stones and sand) and added water. The aggregate usually already contains some water spread over (adsobed onto) the surface of the stones and sand grains, and less water is added to compensate for for this. The mosisture content of the aggregate is continually measured for this purpose. The cement is very dry (anhydrous) but it is made from crystalline rocks (eg limestone) which contain water of crystallisation. Water of crystallisation is water that is incorporated into crystals as they form a solid. This is driven off (by heat) in the manufacturing process of the cement and escapes to the atmousphere. The chemical reactions of the cement and the added water are very complicated but essentially the dry cement powder is recombined with water as water of crystallisation in the new artificial rock that is formed. Excess water percolates to the surface of the freshly mixed concrete as it is worked into place. (Water is of course much less dense than concrete) You can often see pools of water on the top of a concrete 'pour'. Further drying out occurs during the month or so after casting the concrete. The chemical reactions generate heat which increase the drying effect, so much that sometimes the concrete is kept moist on the surface to prevent cracking. So the bottom line is that substantial amounts of excess water is used in the process, but is eventually returned to the environment. The water that is chemically combined with the cement more or less balances the water that was removed in the manufacture of that cement.

Explain what away exactly? The observation that the mean temperature has risen nearly 1o ( which I make at about 5% or 0.34% depending how you base it) since about 1940, whilst the solar radiation has increased by 0.5 w/m2 or 0.037% in the same period? Have there been any attempts to calculate alternative mechanisms for instance the much cleaner air we have over most of the zones that were highly carbon dioxide emissive in the 1940s? IOW are we keeping more of the solar input than before because of CO2 or are we simply receiving more of the input because there is less smog? Or is it even a double whammy?

Good golly gosh man, have you never heard of ice cores? Where do you think they come from, Barbados?

A quick look reveals the following. Cutting back on the Einstein summation convention (much as I hate it) removes the opportunity to distinguish between contravariance and covariance and the distinction between components and projections. In other words the extra stuff that is introduced in moving from vector calculus to tensor calculus seems to be missing when you 'reduce' the tensor set to the cartesian product of two (or more) vector sets. But thanks for the link they papers look sufficiently interesting that you might not hear form me for a while. +1

Thanks for the reply. Just to confirm, you have studied that syllabus or something similar, not you are just starting it ? It seems a pretty standard syllabus to me. The Dutch is better than i feared and i can always ask my relatives in Leiden if I get stuck. My sister-in-law teaches this stuff there. I was going to prepare a sheet with some extensions to outline what you need to know to catch I was talking about in the analysis and leaving the statistics and programming side to other very able members ? erf(x) and its complement erfc(x) are also very important functions in analysis for Engineering and Physics.

This reminds me of a sequence in the remake of Disney's Fantasia https://www.bbc.co.uk/news/world-australia-51036608 Hope spring eternal.

Sounds just like the floods we have been experiencing over the last few years in England. You have my sympathies. Big Government took over flood management from the locals and we have seen two decades of lack of dredging and drainage clearance (too expensive and an accountant told us dredging is not needed !) Just as you say against the advice (=bitter opposition) of the locals who had been managing things for the previous couple of centuries ( by dredging). +1

Are you suggesting the Earth is not a good a point as any other to pick for the centre of the universe? What is your preferred one?

If only it were that easy.

Remember that the units of surface tension are newtons per metre ie force per unit length. So the total hoop or tangential force acting all the way round one line of longitude is the surface tension times the length all the way round the line of longitude, ie T*2πr. Here are 3 different ways to derive your formula. Note how this applies to a soap bubble that has two surfaces, an inner and a outer surface, and a droplet which only has one.

Try the handy answer book series, some of them are rather good and all are modern. The Handy Anatomy Answer Book The Handy Diabetes Answer Book The Handy Biology Answer Book The Handy Chemistry Answer Book etc https://www.visibleinkpress.com/s17/The-Handy-Answer-Book-Series

Forces, not force, it is distributed like the pressure force, but around a line rather than over an area. This sketch may help, it is rather like the intersecting lines of latitude and longitude on a globe. You perform a sum (an integral) of all the longitudinal forces along each line of longitude intersecting an equatorial line of latidude. By symmetry this happens all round each line.

There is no surface tension in the interior of a homogeneous liquid. Surface tension acts at the surface or interface with a different phase, as the name implies. The disk you refer to is in the interior of a homogeneous liquid. The cohesive force you refer to acts at right angles to the surface ring (periphery) you refer to, all around the ring.