6 hours ago, kenny1999 said:

I find that when I cook with oil, if the pan isn't hot enough, the oil runs slowly, but when it gets hot enough, the oil runs faster. How to explain this phenomenon?

There are intermolecular forces acting between the molecules in the liquid, which have to be overcome in order for molecules to slide past one another. At higher temperatures, a greater proportion of the molecules have enough kinetic energy to overcome at least some of these forces, reducing the resistance to them moving relative to one another.  

2 hours ago, MathHelp said:

Hi there,

I wanted to learn some calculus for statistics but it seems like pre-calculus will take many months. If you look at this page from Khan Academy, it does not look like it will be something I can understand for a long time:

Precalculus | Math | Khan Academy

I was wondering if the path to calculus would be shorter if there is something very specific I want to achieve.

What I would like to do is learn one aspect of statistics through calculus - would anyone be able to offer me a roadmap for that? You can choose the part of statistics that the roadmap applies to.

My overall goal is to have a very strong understanding of statistics and eventually understand calculus through statistics. This roadmap would just be a start - I would continue to learn calculus. I happen to find statistics to be a strong motivator for me as I can easily see the direct application to it in my life.

Any help would be appreciated. 

Edit: I'm referring to basic 1st year statistics. Although I am not formally enrolled in a course. I work fulltime and just study a statistics book in my sparetime.

It looks as if this is part of a general mathematical course. Learning basic differential calculus is relatively easy and doesn't require much of all that stuff. I learned it when I was 15, as part of the old UK O-Level syllabus. I don't think statistics helps much with learning calculus. You just need to draw functions as a graph and see how you can make approximations to the slope of the line that, in the limiting case, give you an exact value. There are various videos on this. Looking at them quickly I thought this one was fairly clear.

The chief mathematical idea is the idea of limits, what happens to an algebraic quantity when one variable gets smaller and smaller and tends to zero.   

But then the power of knowing the slope of a function at any point on its graph is that that represents its rate of change. This leads onto all sorts of applications. For example the rate of change of distance with time is velocity and the rate of change of velocity with time is acceleration. Also, the point a slope becomes zero is a maximum or a minimum (or sometimes a point of inflexion) of the curve, so you can find maximum and minimum values of functions this way. And there are lots more applications of course.

Integral calculus is the inverse process, in effect calculating the area under a portion of a curve. There are teaching modules on that too. 

So I think you should be able to short-circuit the modules of the Khan Academy course and go directly to calculus, provided you are OK with algebra and graphing functions and can understand limits. 

(I speak as a chemist rather than a mathematician. It may be that a proper mathematician would disapprove of the short cuts I am suggesting.) 

2 minutes ago, geordief said:

Yes ,I noticed that.Makes it more immediately practical I would think.

 

I wonder if it  is much less costly  to maintain those systems than to develop  them after they have been lost.Does the soil just get washed away  and take hundreds of years to reestablish.

I wonder if the carbon credit economy will take off  as I think I saw mentioned  there or perhaps  it was elsewhere.

 

Would be good if that system worked to the advantage of poorer regions .

 

I noticed that the marshes in Essex (and elsewhere).were being flooded in recent years by punching holes in the sea walls.

 

Would that be the sort of thing they have in mind?

Not sure, but it could be. Salt marsh seems to be what they are advocating.

But actually this marsh stuff is different from your original link, which was about things like kelp and sea grass i.e. actual seaweed, growing under salt water. 

1 hour ago, geordief said:

This seems much better  and goes into much more detail but they are "players in the game" (not that I would be a skeptic for that  )

 

https://www.thebluecarboninitiative.org/about-blue-carbon

Thanks, that is more informative. I notice however that the emphasis is on conserving existing littoral ecosystems, i.e. preventing their loss, rather than developing them as new carbon sinks  to sequester more carbon from the atmosphere.  

11 minutes ago, geordief said:

https://edition.cnn.com/2022/11/02/opinions/mittermeier-nicklen-oceans-blue-carbon-climate-change-scn-spc-c2e/index.html

 

"Opinion: The ocean’s ‘blue carbon’ can be our secret weapon in fighting climate 6"

 

 

This is the first I have come across this idea.

How promising  is it?

 

1. Can we "farm" the seas to sequester carbon from the atmosphere?

The article seems pretty poor at explaining it. There is a handwaving mention of kelp and seagrass but no discussion of the associated carbon cycle. These are plants with finite life. What happens to the carbon when they die? Maybe someone here can comment.

I've a feeling I've seen this silly question before, somewhere. 

On 10/29/2022 at 12:08 PM, studiot said:

https://www.bbc.co.uk/news/uk-scotland-63402811

 

 

Just look how low this dam is.

Surely the relevant question is how high this lake or tarn is above the generating station, i.e. the head available for power generation. In the Highlands, one of the things that is free is height. 

1 hour ago, Eise said:

Oh, I nearly always see steel constructions in thunder clouds ...

OK, without joking, there is a nice subtle difference in Kevin's thunderstorm, and real-life thunderstorms. With Kevin, all the droplets fall downwards. So my guess is that this construction is needed, because otherwise the influence can not be self-amplifying. In real thunderclouds of course we have up- and down-streams, making steel constructions unnecessary. 

Indeed. If you read my description of the inductive mechanism in the OP, it explains how that can take place.

1 hour ago, trevorjohnson32 said:

Hey Exchemist, hot handing my question from the other forum ay?

I think we need to look at the difference between non lightning rain clouds and lightning bearing rain clouds. Both are going to have friction in the clouds. Could perhaps the keys lie in the clouds reaching up to a higher level of ionsphere? Perhaps the heat from humidity rises and collects in the ionsphere and produces lightning that is attracted to the heavy metal on and in Earth?

The electrosphere layer (from tens of kilometers above the surface of the Earth to the ionosphere) has a high electrical conductivity and is essentially at a constant electric potential.

Storm clouds are 6-12 miles high.

So as gravity tapers off into the exosphere, it gets colder and probably more conductive, or it could be conductive from Earth's magnetic field, or a combination of the two, the clouds reaching up so high are like wires for the heat on the surface up into the colder regions, then the heat converts to electricity probably from running water through the conductive zones, or maybe something else, and of course then you get lightning.

Yes Trevor it was stimulated by the research I did on this arising from your question on the other forum. There are more scientists here, so there is more of a chance of getting further with the topic.  Suggest you read and learn, and refrain from outlandish speculations. 

28 minutes ago, studiot said:

No I don't think so.

For a start that machine requires large continuous metallic conductors AKA wires in the sky.
Last time I looked I didn't see any.

Secondly you quite rightly identified upward movement as well as downward movement.
Again I don't see this in the machine.

But many thanks for bringing this gadget to my attention.
I had not heard of it before.
If you listen to others, you can learn somthing new every day.

+1

 

The Maynard model I referred to is the result of many measurements of the electric field at various altitudes and is used in the flying industry for calibrating navigation equiment.

It is a capacitive model.

It also has both upward and downward movement of particles.
It was the result of a geat deal of research in the decades mid 1940s to mid 1960s.

Curiously, Maynard's name does not appear in the review of the various models that I linked in the OP. A lot of work has been done since the 1960s, so it may have been superseded.

Rather than sending me 10 pages by PM, is it possible for you to post a short summary of its key features?

1 hour ago, Eise said:

Kevin's Thunderstorm? See here, from Veritasium.

Are clouds with upgoing and downfalling drops and ice crystals not gigantic influence machines, so to speak wet versions of the Wimshurst machine?

Which, of course as nothing more than you suggest...

Nice. This seems to be the inductive model, more or less. 

8 hours ago, Scienc said:

So, is the true value for work +22, because work is done on the system?

I used the 𐤃U = q+w. because I studied in a chemical class. However, I considered the contribution to work as negative. The book on the other hand, used a positive signal for work.

The images is from the book.

I think it best to keep in mind what is happening physically, to ensure your answer makes sense. If there is a volume reduction, the atmosphere is compressing the system. Then as @sethoflagossays, that adds internal energy, so if what you get out as heat is less than this, the net internal energy must have gone up, so ΔU has to be +ve.   

But I confess I too was thrown by the term "expansion work" when in fact what happens is the opposite, viz. compression work - at least from the system's point of view. It may be that the learning point for both of us is what @sethoflagos says about "expansion work" being used to denote any form of PdV work, regardless of whether it is expansion or compression of the system. I was never taught this terminology. We always spoke of "PdV work" and left it at that, which is far less confusing in my estimation. 

50 minutes ago, studiot said:

I'm sure this graph is relevent.

 

https://www.researchgate.net/figure/Breakdown-voltage-in-air-versus-relative-humidity-with-an-alumina-surface-Electrode_fig17_3165903

What does this tell us about the mechanism by which charge separation takes place in thunderclouds?

1 hour ago, Scienc said:

I have a question about the resolution of this exercise: 

 

I tried to solve this problem with the following steps:

 

For the 1º law of thermodynamics, 𐤃U = q+w.

As q = 𐤃H at constant pressure, I assumed that in this process q = - 15 kJ.

 

As a result, 𐤃U = -15 - 22 (because was an expansion) and for this reason, 𐤃U = -37 kJ.

 

However, the book has this resolution

 

I understood why the book used this method, but I did not understand why my method is wrong.

I wonder if this is to do with  the wording. They say 22kJ is expansion work done "on the system". They don't say 22kJ of expansion work is done by the system. 

Presuming "the system" means the reactant and products, I'm confused as to whether the atmosphere does work on the system, i.e. the volume decreases in the course of the reaction, or whether the system does work pushing back the atmosphere, i.e. the volume increases. 

If the volume increases, then I agree the internal energy change must be enough to supply that work AND still give you a measured heat output of 15kJ. 

1 hour ago, MigL said:

Liquid water and ice, moving through the air, tend to build charge.

An example you may be familiar with ( if you were an industrial chemist ) ...
You never have a liquid like IPA, or Toluene, etc., free falling into a tank.
You should always have a dip-leg to prevent charge build-up

From my experience in the oil industryI'm aware of static generation in insulating liquids flowing in a pipe or in charged droplets in water sprays, used in tank cleaning etc, but I don't believe I've come across the idea that liquid falling through air does this to a significant extent.

25 minutes ago, MigL said:

Charge separation between the upper and lower parts of the cloud would indicate that the eventual discharge ( lightning ) would occurr within the cloud itself.
Most all lightning I've seen discharges between the earth and cloud, indicating that is where charge separation occurrs, and the mechanism would be similar to rubbing a balloon on your hair, or rubbing an amber rod with fur, or ...

The mechanism discussed in your link, may contribute, but it doesn't explain the lightning or its path.

Cloud to cloud discharges are extremely common in thunderstorms.

But my interest is in the charge separation mechanism. Handwaving about the triboelectric effect (which by the way also seems poorly understood) doesn't seem to help very much. 

Regarding cloud to ground discharges, my understanding is that it is the charge separation within the cloud which causes a polarisation of the earth beneath and that is what leads to a lightning strike. I've never heard of any triboelectric effect involving the earth (what would "rub" against the earth and how would that work?).  

51 minutes ago, dimreepr said:

This is an interesting watch on the subject (hope you can view it).

It may be but it seems to address a different issue, viz. how the lightning discharge occurs. Does it actually discuss the mechanism of charge separation? I'm not going to waste time watching a video that may be irrelevant to what I'm trying to understand. 

Due to a question asked on another forum, I tried to look into the mechanism by which charge separation takes place in thunderclouds. To my surprise it seems we still don't know how it happens.

I found this paper, summarising the various hypotheses and the drawbacks of each: https://www.researchgate.net/publication/227134643_Charge_Separation_Mechanisms_in_Clouds

Apparently the leading hypotheses are an inductive mechanism, relying on polarisation of liquid water droplets and one involving charge transfer between "graupel" (soft hail) and ie crystals.

The inductive hypotheses relies on the idea that the electric field within the cloud (+ve at the top and -ve at the bottom) polarises the larger droplets, which are falling under their weight, so that they become positively charged at their base. When they encounter small droplets, which are rising due to the convective updraught in the cloud, they abstract electrons, leaving the small droplets with a +ve charge.  So this leads to a further accumulation of +ve charge at the top and -ve at the bottom, further strengthening the electric field and so on.   

The ice one was more intriguing. Experiments at Manchester University have apparently shown that when falling lumps of graupel contact ice crystals, charge tends to be transferred, the extent and polarity of the transfer depending on the temperature. I found myself wondering why there should be a difference in tendency to lose electrons - or protons - (it is unclear which are the charge carriers in the interaction) - between crystalline ice and the presumably more amorphous ice in graupel. I wonder if it may be to do with the edges and vertices of crystals. There will be unsatisfied valencies there, since the molecules at such locations are not fully bound into the lattice in all directions. The paper doesn't go into this, being more concerned with the physics of the overall process. 

Anyway, it seemed interesting that this is not yet well understood. I wondered if anyone here might know more about the subject. 

1 hour ago, iNow said:

I've seen this, too. Really neat stuff. Have been considering putting a bit of it in my kids stocking for the holidays. Would love to know from people better informed than myself if there's any noticeable risk.

Metallic gallium seems to have low toxicity. From what I read it behaves more or less like Fe in biological systems. I don't think handling a bit of it will do any harm.

6 hours ago, John Cuthber said:

Moonshine...

Eh??

2 hours ago, Deepak Kapur said:

1. But, if ToE is formulated...won't it mean that we have reached something, which has to be taken as a 'given'.

2. If there is always something more to discover, doesn't it mean that 'the never ending exploration' is to be taken as a 'given'?

Re your  (1) no, any ToE will remain subject to the possibility of refinement, modification or rejection, in case there may one day be new observational evidence that does not fit with it. Science aways stays open-ended, as we can never know there are no more novel observations to be made.

Re your (2), never ending exploration has always been a given in science: it is intrinsic to what science is. 

14 minutes ago, Willem F Esterhuyse said:

Here is a synopsis attached.

Proof of Axioms - Synopsis.docx 5.19 kB · 0 downloads

You've already got one thread on this subject AND you've been told not to just attach files with no explanation.

Reported. 

On 10/23/2022 at 1:43 PM, John Cuthber said:

Am I the only one who regrets the passing of metal biscuit tins and their replacement by plastic ones?

Ah, so the meringues I make are hardened against an EMP, then. Good to know.

56 minutes ago, kenny1999 said:

Does white colored object actually reflect all UV so that it is free of being attacked by UV?

or is it also attacked and dyed by UV but since it's white you can't see the effect?

Another question is we know that white clothes is cooler in the summer than black clothes, is it because most light is reflected by white color?

White objects do not absorb , or not much, in the visible region of the spectrum. But UV, as the name implies, lies outside that region. So visible colour is no guide.

White clothing absorbs less visible light, which indeed makes it heated less by sunlight.

1 hour ago, Deepak Kapur said:

Let's go in distant future. Let's assume that science has discovered all the fundamental particles/concepts that explain this universe completely.

 

My questions are as follows:

 

1. Won't these fundamental particles have to be taken as a 'given' (with no further explanation possible)?

 

2. Is this the ultimate future of science...to reach at something, which has to be taken as a given?

You can never make such an assumption, so this scenario can never arise. 

This is because It is never possible to prove a scientific theory true. So we can never state with certainty that there is no more to discover.