48 minutes ago, sethoflagos said:

You got me thinking. It's true as you say about Archimedean buoyancy, but it does affect the (much smaller) amount of nett uplift he would get from surface energy differences due to the local radius of curvature of the interface. Per the Kelvin equation, a long thin cylinder is about the optimum geometry for this. More so if he rubs on a thin layer of goosefat to increase the difference between cohesive and adhesive forces at the interface. A somewhat rounded figure may also help as AFAICT, a flat faced cube would only get a little uplift along the edges.

You mean surface tension, like a pond skater? That would depend on the length of the contact line between water and skin. But surely the effect would be negligible, wouldn’t it?

29 minutes ago, exchemist said:

You mean surface tension, like a pond skater? That would depend on the length of the contact line between water and skin. But surely the effect would be negligible, wouldn’t it?

Don't forget that from a thermodynamics pov, surface tension and surface energy are basically the same thing, applied to fluids and solids respectively for historic reasons.

Leastwise, the surface tension (N/m) and surface energy (J/m²) of water have the same numerical value (~ 0.0725), which is only 10% or so less than that of soda glass. Which is one reason why under certain circumstances, Navier-Stokes ceases to apply and their 'fracture' mechanism can become comparable.

Yes, it's true that on a metre scale with a Bond number ~10⁴+, then gravitational forces will dominate. But surface tension effects never go away, and around the centimetre scale (Bond number ~ 1) they become comparable (ie a chemical engineer ignores one of the pair at his peril).

Chem Eng humour includes defining the inverse of the Bond number as the 'Jesus number' since having a large one may enable you to walk on water. You've got to find something to laugh at when designing gas flotation units for effluent treatment works.

3 hours ago, sethoflagos said:

Don't forget that from a thermodynamics pov, surface tension and surface energy are basically the same thing, applied to fluids and solids respectively for historic reasons.

Leastwise, the surface tension (N/m) and surface energy (J/m²) of water have the same numerical value (~ 0.0725), which is only 10% or so less than that of soda glass. Which is one reason why under certain circumstances, Navier-Stokes ceases to apply and their 'fracture' mechanism can become comparable.

Yes, it's true that on a metre scale with a Bond number ~10⁴+, then gravitational forces will dominate. But surface tension effects never go away, and around the centimetre scale (Bond number ~ 1) they become comparable (ie a chemical engineer ignores one of the pair at his peril).

Chem Eng humour includes defining the inverse of the Bond number as the 'Jesus number' since having a large one may enable you to walk on water. You've got to find something to laugh at when designing gas flotation units for effluent treatment works.

OK so 0.07N/m. Let's say someone spread-eagled on the water has a total waterline length of 9m. That will generate ~0.6N of upthrust, compared to a body weight , for a (light) 60kg person of ~600N, i.e. of the order of 0.1% of what is required to make them float. But away from the question about floating bodies, yes at the cm scale surface tension starts to make itself felt. I have a badly designed colander with 0.5cm holes in stainless steel and I can never get things in it to drain properly. My parsley, coriander or whatever is always dripping wet, no matter how long it is left to drain.

3 hours ago, sethoflagos said:

Don't forget that from a thermodynamics pov, surface tension and surface energy are basically the same thing, applied to fluids and solids respectively for historic reasons.

Surface tension is part of a select set of pairs of quantities, one intensive, one extensive, whose product has the dimesnions of energy.

Others include

Magnetic Field H and magnetic momentM
Electromotive Force F and Charge Q
Pressure P and Volume V
Tension T and distance L
Temperature Theta and Emtropy S.

It is this last one I like to use to explain entropy simply.

On 4/11/2026 at 1:50 PM, paulsutton said:

Interesting geological / geochemistry differences given Devon and Somerset are next to each other, how do they contrast with Dorset ?

Questions / Comments like these are great since they halp me see what you made of my previous ramblings..

OK so compare and contrast the geology of Dorset with that of Somerse/Devon.

The first and most startling thing is perhaps that when Devon / Somerset was being formed Dorset did not exist !

Here is a map of UK Geology today.

The first thing to notice is the the colours representing diffent rock eras or periods run in diagonal stripes (of variable width) from South West to North East.
What is important is that these stripes are getting younger (more recent as you go at right angles to the first direction ie from North - West to South East.

The bright yellow stripe (this represents Jurassic rocks) runs from the Somerset and Devon border with Dorset diagonally up through the Midlands, across the Humber and runs out into the North Sea via the North York Moors. This includes the limestones of the famous 'Jurassic Coast' and the Lias of Somerset.

The Khaki stripe represents the transition from the the Jurassic into the younger Cretaceous and the proper green the full on Cretaceous ~ Chalk.

The next map shows that Dorset lies firmly in the Western end of the so called Wessex basin.

It is worth noting at this stage that the Wessex Basin extends well into the English Channel so the larger part of it is under water.

To understand how all this came about it is necessary to go back to the formation of the earth 4600 million yars ago (MYA).
But then move very quickly forward as the British Isles themselves did not exist until a couple of hundred million years ago and that all the areas South East of the the yellow triassic band have been created since 280 million yeas ago. That is the chalk and clays of the Home counties and East Anglia.

I will explain this next time in more detail, but I am also aware that I haven't finished my explanation of loads, forces and stresses.
I will do that after.

So keep the questions and comments coming as feedback.

Edited April 12Apr 12 by studiot

On 3/30/2026 at 8:04 PM, studiot said:

That's true.

In fairness both mica and talc occur more often as minerals in some rock eg granite.

The result of granite weathering creates many small mineral flakes that go twoards the clay soil.

The South West batholith granite is vey coarse grained which leads to easy breakdown and the fine china clays of Cornwall and coarser clays in Devon.

Somerset has a completely different geology with the sedimentary clays, sandstones and mudstones the result of run off from the edge of a former continental margin.

There are almost no igneous rocks in Somerset an exmoore is sedimentary, unlike Dartmoor, Bodmin and the other cornish moors.

Known examples of liquid fracture under gravity.

Now contrast this with the behaviour of separation drops (fractured water stream) from a dipping/slow running tap

That is pretty cool, I wonder what he would think about the fact that his experiment is still going after nearly 100 years, Then again look at the 1/2 life of some radioactive isotopes, some take seconds others take days, months or even years.

4 hours ago, paulsutton said:

That is pretty cool, I wonder what he would think about the fact that his experiment is still going after nearly 100 years, Then again look at the 1/2 life of some radioactive isotopes, some take seconds others take days, months or even years.

Uranium-lead radiometric dating makes use of an isotope with a half life of billions of years: https://en.wikipedia.org/wiki/Uranium–lead_dating

Mind you, I’m buggered if I know how the hell they determine a half life that long. Must be by dating rocks using other, shorter, half lives, I imagine, and then inferring from that the half life of U238.

4 hours ago, exchemist said:

Mind you, I’m buggered if I know how the hell they determine a half life that long.

It's actually not that hard. You don't have to wait 4.5 billion years for a u-238 sample to decay to half strength, simply measure how the radioactivity decreases over a certain time and extrapolate to when it would be at half and you have just determined half life. You just need equipment capable of detecting minute changes.

Edited April 14Apr 14 by npts2020
clarification

3 minutes ago, npts2020 said:

It's actually not that hard. You don't have to wait 4.5 billion years for a sample to decay to half strength, simply measure how the radioactivity decreases over a certain time and extrapolate to when it would be at half and you have just determined half life. You just need equipment capable of detecting minute changes.

Sure. But with a half life that long, I'd have thought you would never be able to measure a discernible decrease in radioactivity.

But thinking more about it, I suppose with a big enough sample, if you can detect every individual decay event, you can count the decays of individual atoms and, knowing how many atoms there are in your sample, you can work out the decay rate that way.

The half life of U235 to Pb 207 is 710 million years

The half life of U238 to Pb 206 is 4470 million years

Both are used, preferably in zircon crystals as a cross check for each other.

https://www.amnh.org/learn-teach/curriculum-collections/earth-inside-and-out/zircon-chronology-dating-the-oldest-material-on-earth

On 4/12/2026 at 6:58 PM, studiot said:

Surface tension is part of a select set of pairs of quantities, one intensive, one extensive, whose product has the dimesnions of energy.

I find the ratio of latent heat of vapourisation to surface tension quite a fascinating subject. You can just about measure reasonable values for each in kitchen experiments and they yield an interesting probe into molecular scale.

Take a sphere containing a gram mole of water. It has a:

Volume of 0.000018 m³

Radius of 0.01626 m

Surface area of 0.003321 m²

This sphere can be subdivided (bear with me) into n³ spheres of radius/n and n times the total surface area. Now taking:

Molar latent heat of 40,700 J mol^-1

Surface tension of 0.0725 Nm^-1 = Jm^-2

Yielding a ratio of 561,379 m²mol^-1

Taking the ratio of this to the molar surface area quoted above we get the following estimates:

n = 169,039,238

Particle radius = 0.0962 m^-9

Number of particles = 4.83 * 10²⁴

Getting within 1% of the OH bond length is mainly coincidental I suspect, but the 8-fold overestimate of Avogadro's, (corresponding to n being out by a factor of almost exactly 2.0) is also curious.

Edited April 15Apr 15 by sethoflagos
9 orders of magnitude

21 hours ago, exchemist said:

Uranium-lead radiometric dating makes use of an isotope with a half life of billions of years: https://en.wikipedia.org/wiki/Uranium–lead_dating

Mind you, I’m buggered if I know how the hell they determine a half life that long. Must be by dating rocks using other, shorter, half lives, I imagine, and then inferring from that the half life of U238.

I was thinking that, given that 1 mole of a substance still has the same number of atoms, e,g 1 gram of Hydrogen and 238 grams of Uranium would still have 6.022 x 10^23 atoms. So they may calculate based on that, and as you said infer the 1/2 life.

Maybe that is a question for another thread.

To continue

We need to go back to the beginning to understand how, when and where the different types of rocks and chemicals arise.

So 4.6 billion years ago the Earth was a ball of molten (i.e. very hot) material.
Gravity caused some differentiation of the constituents.
As the ball cooled the outside reached solidification temperatures before the inside, so forming thin solid crust.
As this crust continued to cool it shrank and cracked into a pattern of crazing, as does drying mud or concrete or resin.
As a result hotter liquid material pushed up from below through the cracks and spilled onto the surface of the already solid material building it up further.
Also some of the patches completely separated from each other forming tectonic plates.

The important point for Dorset geology is that.

This material is, by definition, all igneous material. There were no other types of rock on the planet at that stage. Igneous rock is formed directly from cooling molten rock, called magma.
There is no igneous material in Dorset. All this early buildup went to form the 'shield areas' in say Australia, Canada, South Africa, Siberia etc...

After half a billion years or so it rained for about a billion years. The combination of erosive forces generated a source of sediment material along with an ocean to distribute it in.
Thus commenced the erosion - transportation - deposition cycles that would eventually form the sedimentary and metamorphic series of rocks in Dorset.

Life also started on Earth about this time, towards the end of the ‘rainy season’.
This is important for Dorset since nearly all chalk requires life to form.
The Jurassic series has both biological and non biological origins.

Fast forward another 2.5 billion years with more igneous production, erosion - transportation and deposition cycles and two new forms of rock type appeared as well.
These cycles led to sedimentary rocks being laid down.

The other new type being metamorphic rock.
Rock that has been altered by either heat and/or the pressure of the load above it.
The process of Metamorphosis take place in both igneous and sedimentary rocks.
Dorset has both unaltered sedimentary rocks, such as the chalk and clay, and altered sedimentary rocks such as Lias and shale.

We arrive at a time between 500 MYA and 600 MYA. for a further look at the world.
There was a large continental mass centred on the South Pole called Gondwana and a series of smaller lands , Laurentia, Baltica etc.

Laurentia being basically North America and Baltica being Scsndinavia, North Western Europe and North Western Russia.
The rest was ocean.

We are now in the Cambrian period and the beginnings of the British Isles can be seen on the map.
Northern Scotland and Northern Ireland are shown as small red blobs on the coast of Laurentia, Southern parts are shown on the other side of a former ocean as part of Gondwana.

It should not be thought that either looked anything like modern Britain, as many parts had yet to be formed.

As already noted plate tectonics was moving things about, so the next stage shows a convergence of lands, but Gondwana beginning to break up.
In particular a new fragment called Avalonia, carrying the future England and Wales, detached.

This takes us into the early Ordovician period. 500 to 460 MYA.

This process continued throughout the Ordovician and Silurian periods, with further detachments from Gondwana and continued closing of the old ocean called the Iapetus ocean.

A new ocean was opening between Gondwana and the other plates.

England/Wales and Scotland were now very close together.
We are now at about 435 MYA and the Ordovician is coming to an end.

At 425 MYA we are into the Silurian period and Lautrentia and Baltica are now joined to Baltica by a land bridge formed from Avalonia.
This new large land mass is now separated from a much reduced Gondwana by the opening Rheic ocean.
It should be noticed that that this new land mass is bang on the equator. The Silurian is note for hot dry conditions.

At around 400 MYA the Iapetus ocean finally closed with a bang.

The bang being the formation of a great mountain range, known as the Caledonian Mountains.

This was the Caledonian Orogeny (orogeny = mountain building)

And this ushered in the Devonian period when Britain came together in what is known as the Iapetus Suture,

During the next hundred million years there was more activity during which a new ocean (the Atlantic) opened, separating Britain (as was) and the rest of Europe from North America.

Devon and (West) Somerset were formed by the sedimentary and pressure metamorphic process as previously noted and the Carboniferous period followed the Devonian.
But the granite intrusion of Devon and Cornwall had not occurred at this stage both were still sedimentary/ pressure metamorphic.

But none of this really affected Dorset, which had yet to be formed.

So the third part of the Dorset story will come in the next instalment.

Questions ?

2 hours ago, studiot said:

There is no igneous material in Dorset. All this early buildup went to form the 'shield areas' in say Australia, Canada, South Africa, Siberia etc...

2 hours ago, studiot said:

But none of this really affected Dorset, which had yet to be formed.

Surely this only applies to the surface geology of Dorset. At depth, it's underlain by a continental crystalline basement of up to 1bya followed by a great depth of later sediments. See Wikipedia entry on the London-Brabant Massif, particularly the 'Formation' section.

The massif is composed of crystalline basement (metamorphic and igneous rocks) with Proterozoic to early Paleozoic ages. It was deformed and metamorphosed during the Cadomian orogeny (Ediacaran, about 600 million years ago) and Caledonian orogeny (Silurian, about 420 million years ago). This basement is almost everywhere overlain by younger sedimentary rocks, except for some places in the southwest of England and in Wales.

19 minutes ago, sethoflagos said:

Surely this only applies to the surface geology of Dorset. At depth, it's underlain by a continental crystalline basement of up to 1bya followed by a great depth of later sediments. See Wikipedia entry on the London-Brabant Massif, particularly the 'Formation' section.

Did you also read this bit in Wiki ?

The massif is composed of crystalline basement (metamorphic and igneous rocks) with Proterozoic to early Paleozoic ages. It was deformed and metamorphosed during the Cadomian orogeny (Ediacaran, about 600 million years ago) and Caledonian orogeny (Silurian, about 420 million years ago). This basement is almost everywhere overlain by younger sedimentary rocks, except for some places in the southwest of England and in Wales.

The continent Avalonia was until the Ordovician (465 million years ago) part of the large southern continent Gondwana, but then began drifting independently to lower latitudes. As it passed through the dry latitudes represented today by the Namib Desert¹, it was eroded and the soils became laterite. The strata, particularly of the Precambrian are complex. Their continuity is also poorly understood because they are beyond the reach of most boreholes.

So it is entierly consistent with the story I am developing for Paul.

Avalonia is shown in my diagrams.

But note the comment "beyond the reach of most boreholes"

I could make the same comments aboutthe mantle.

Whatever rocks underly the sea and lake floors were obviously there at the time I referred to as Dorset did not exist, and continued to be there subsequently when the sediments that make up modern Dorset were being laid down, with some subsequently metamorphosed. The the Dorset oilfield is jurassic/cretaceous not carboniferous.

The rocks I am referring to are obviously what the BGS call Solid geology on their maps.

There are also Drift maps.

But there is much still unknown about the SW peninsular and there are some suprises to come so keep the discussion going.

Edited April 15Apr 15 by studiot

2 hours ago, studiot said:

Did you also read this bit in Wiki ?

Yes. It's the shared geological heritage of most of England, Wales, and Eire save for bits of Cornwall and the bottom half of the Isle of Wight which we gained a little later from the Normannian terrane.

2 hours ago, studiot said:

Whatever rocks underly the sea and lake floors were obviously there at the time I referred to as Dorset did not exist,

It's just a really strange way of putting it. At exactly which horizon do you suggest it stops being Dorset? Surely not the 2,000 m thick Triassic Sherwood Sandstone Group of the New Red Sandstone that outcrops famously at Budleigh Salterton and (obviously) Sherwood Forest among many other locations? Or the underlying Devonian marine cousins of the Old Red Sandstone supergroup that Dorset shares with... well, Devon?

I can understand you thinking that Dorset is something special geologically: it is! I spent many happy hours fossil hunting Black Ven. But treating it as an isolated little island like Big Island Hawaii (that really is only 400,000 years old) risks losing all context of its rich shared history with the rest of the country, which really is a lost teaching opportunity.

Plus, given recent events, if we don't nail our flag to the underneath bits, Trump's likely to send Thunderbird's Mole unit in to annex it.

7 minutes ago, sethoflagos said:

Yes. It's the shared geological heritage of most of England, Wales, and Eire save for bits of Cornwall and the bottom half of the Isle of Wight which we gained a little later from the Normannian terrane.

It's just a really strange way of putting it. At exactly which horizon do you suggest it stops being Dorset? Surely not the 2,000 m thick Triassic Sherwood Sandstone Group of the New Red Sandstone that outcrops famously at Budleigh Salterton and (obviously) Sherwood Forest among many other locations? Or the underlying Devonian marine cousins of the Old Red Sandstone supergroup that Dorset shares with... well, Devon?

I can understand you thinking that Dorset is something special geologically: it is! I spent many happy hours fossil hunting Black Ven. But treating it as an isolated little island like Big Island Hawaii (that really is only 400,000 years old) risks losing all context of its rich shared history with the rest of the country, which really is a lost teaching opportunity.

Nowhere have I said that I consider Dorset geology to be something special.

But I was asked to compare and contrast with that of Devon and Somerset, whose geology is definitely different.

There are multiple questions to be asked, some being quite complex, such as the source of the constituent materials for the rocks we see, for instance the proportion of garnets in the sandstones.

Nor do I consider what I am saying strange.

What would be strange would be claiming that Dogger Bank is part of Britain, today.

Yes it once was so people walked across the land connection and lived there.

But today Dogger is part of the North Sea floor.

My presentation has not yet come to placement mechanisms such as folding, thrusting, faulting, uplift etc.

Nor have I yet added in the effect of sea level changes.

There is a real question as to why the rocks of the SW peninsula (Cornwall, Devon and Somerset) are not similar to those of Wales and the Midlands, but are very different, despite all being called Old Red Sandstone.
There is currently no model that answers this except the very recent one that requires a 400km displacement along the Bray fault, transferring the whole peninsula from former Avalonia to former Armorica.

47 minutes ago, studiot said:

But I was asked to compare and contrast with that of Devon and Somerset, whose geology is definitely different.

... that can't be explained by the national general ESE dip in sedimentary structures? Different thread maybe? You've strayed a very long way from rotational shear landslides that had perhaps some tangential relevance to the OP.

10 hours ago, studiot said:

There is a real question as to why the rocks of the SW peninsula (Cornwall, Devon and Somerset) are not similar to those of Wales and the Midlands, but are very different, despite all being called Old Red Sandstone.
There is currently no model that answers this except the very recent one that requires a 400km displacement along the Bray fault, transferring the whole peninsula from former Avalonia to former Armorica.

... or to put it another way:

A solution is proposed by Woodcock et al. (2007) that a terrane, termed Prettania (most likely NW Iberia), lay where SW England is now positioned and that the Rhenohercynian Zone lay some 400 km to the southeast. Carboniferous dextral movement along the Bristol Channel-Bray Fault Zone then translated SW England to its current position (Figure 1), but a mechanism for synchronous Acadian deformation and Rhenohercynian extension is yet to be satisfactorily explained (Holder and Leveridge, 1986; Leveridge and Shail, 2011; Woodcock et al., 2007).

This isn't firmly established science. It belongs in Speculations.

On 4/16/2026 at 10:58 AM, sethoflagos said:

... that can't be explained by the national general ESE dip in sedimentary structures? Different thread maybe? You've strayed a very long way from rotational shear landslides that had perhaps some tangential relevance to the OP.

... or to put it another way:

This isn't firmly established science. It belongs in Speculations.

There is very little firmly established in Geoscience and I have been careful to signpost the difference between an hypothesis and more solid (pun intended) data.

For anyone interested there is a pretty new (post 2023) programme on PBS America about plate tectonics. today.
It is due to be repeated twice more today and can then be found on catchup.

The planet of the plates.

I found a book in a charity shop on Structural Mechanics which seems to cover some (or may be all) the topics @studiot is covering so I I will give that a read too.

4 hours ago, paulsutton said:

I found a book in a charity shop on Structural Mechanics which seems to cover some (or may be all) the topics @studiot is covering so I I will give that a read too.

OK so you are still with the program.

😀

Remember that structural mechanics is mostly about statics, so don't get to bogged down in frameworks, which an older book will probably be mostly about.

Some stress related comments I have been holding back might be helpful in your reading.

It is tempting to say that Stresses are internal forces due to applied loads and that it is impossible to apply external stress.

Furthemorer strains are the results of the stresses and thus indirectly the results of the external loading.

This is how the subject is often taught.

Unfortunately Nature refuses to fit in to the human preconception and desire to categorise everything into neat little boxes.

So although this is a good rough guide Nature provides for a mechanism to apply an external stress , and a way to have internal stress without strain (particularly applicable to geology) and strain without stress.

A good way to think of stress is as I started with the bouyancy diagram, remember I said there is a lot more to this simple example than old Archie got out of it.

So, for the moment, think of stress as a distributed force (where its action is distributed along a line or over an area or through a volume) rahter than having a single point of action.

But just be ready for nature to bite us in the arse again when we come to consider forces at right angles to the normal force.

Yes, Nature does have a canny ability to throw a spanner in the works of current thinking, Even the JWST is re writing our understanding of the universe early history, so as you said nature has many things that don't fit.

Once we reach the moon, we will probably end up re-writing everything on stress based on what we learn in micro gravity on the moon. Different environment will throw up more problems, just that the stakes will be much higher i guess, as we can't evacuate a moon base.

As we are talking about materials and stresses, what do people make of this?77

'It's crazy' - villagers mystified as river dramatically changes course

https://www.bbc.co.uk/news/articles/cqxlv7x1527o

Would there be a connection, it does look like human intervention by land owners may have had unexpected consequences.

56 minutes ago, paulsutton said:

Yes, Nature does have a canny ability to throw a spanner in the works of current thinking, Even the JWST is re writing our understanding of the universe early history, so as you said nature has many things that don't fit.

Once we reach the moon, we will probably end up re-writing everything on stress based on what we learn in micro gravity on the moon. Different environment will throw up more problems, just that the stakes will be much higher i guess, as we can't evacuate a moon base.

As we are talking about materials and stresses, what do people make of this?77

'It's crazy' - villagers mystified as river dramatically changes course

https://www.bbc.co.uk/news/articles/cqxlv7x1527o

Would there be a connection, it does look like human intervention by land owners may have had unexpected consequences.

Yes I too saw that fairly uninformative news article. There is no "before and after" diagram or aerial shot to give any clue about what may have happened. It is normal for meanders, for instance, to become increasingly extreme until the river breaks through, leaving what is known as an "oxbow lake" in the dead meander. But it doesn't look like that here. There isn't enough information to comment.

But this doesn't seem to me to have anything to do with the thread topic.

10 hours ago, paulsutton said:

As we are talking about materials and stresses, what do people make of this?77

'It's crazy' - villagers mystified as river dramatically changes course

I agree with exchemist the BBC article is too poor to properly see what is going on but I suspect the current river/stream is what is called a misfit river/stream, especially considering its location in a formerly glaciated part of Wales.

I see Google no longer give a link to it's search so I suggest you put this term into google.

The Wiki article is also poor.

A misfit river (or stream) is a stream that is either too large or, more commonly, too small to have eroded the valley or passage in which it currently flows. These rivers often meander through large, flat-bottomed U-shaped valleys that were previously carved by much larger glaciers or higher water volumes, making them appear disproportional to their landscape. 

Key Characteristics and Causes

• Glacial Legacy: Frequently found in glacial troughs where the initial glacier was far wider and deeper than the current river.

• River Capture: Formed when a "captor" river erodes a watershed and diverts the flow of another ("captured") river, leaving the original river valley with only a tiny, under-fit stream.

• Climate Change: Changes in climate can significantly reduce a river’s flow, leaving it with a reduced volume (discharge) that does not match the size of its original valley.

• Appearance: They are often meandering, small streams flowing through wide, flat, formerly carved-out channels. 

Examples include the current River Solva in Wales.

Misfit rivers are well known for changing their course.

On 4/23/2026 at 6:50 PM, paulsutton said:

I found a book in a charity shop on Structural Mechanics which seems to cover some (or may be all) the topics @studiot is covering so I I will give that a read too.

It could be useful to know what is the title and author of this book. I might even have a copy.

Books on structures, theory of structures, mechanics of structures etc tend to concentrate on the loadings applied to the structure and the deflections (of the structure as a whole) that result from these loadings.

Books on mechanics of materials, strength of materials, elasticity, plasticity tend to concentrate on the internal forces and stresses generated in structural elements as a result of the loadings and how these internal forces and stresses are transferred from one structural element to another, for instances in reinforced concrete how they are shared between the steel and the concrete.

There is much overlap between the subjects

To press on with my explanations, which should be a help in reading this stuff;

Consider a catapault or bow and arrow.

We finally come to figs2 to 4

This shows the path of the projectile down the middle of the page and the elastic or bowstring at right angles across this line.

This model provides us with a non mathematical intuitive guide to combining or splitting forces.

In Fig 2 common experinece tells us that the tension in the string or elastic must be the same either side of the projectile, in order for the projectile to fly true down its middle path.

Equally it tells us that there can be only one force acting on the projectile as there is only one path.

So we deduce that the two tension forces can be replaced by an equivalent single force as shown in Fig 3

So if we can combine two forces to a single one we can also go the other way and replace a single force by two (suitable) forces.

In Fig 4 I have shown this split done for each of the two tension forces, now shown dashed and red and blue.

Hopefully it is immediately obvious that the red and blue cross forces at right angles to the path are equal and opposite so cancel each other out.

This leaves the red and blue forces both pointing in the same direction along the flightpath so reinforcing each other or adding up.

Such a splitting is called resolving into components so each (red and blue) force is resolved into two components, one along the flightpath and one at rightangles to it.

We use this technique over and over again in mechanics.

It works for forces but cannot be done for stresses - but we will come to that.