1 hour ago, exchemist said:

I thought talc was sometimes classed as a clay mineral though. It too has sheets only bonded by van der Waals attraction, I think. With mica I think there is a cation between the sheets.

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

Edited Monday at 07:38 PM4 days by studiot

18 hours ago, MigL said:

Granular solids can be made to act like liquids.
We regularly 'float' Sulphur prills, or flakes, on a cushion of N2 pressure, so it acts 'liquidy', and we can suck it under vacuum into a reactor for dithionation processes ( flakes need different N2 pressure than prills ) at my work.
This effect is also seen in avalanches and land-slides.

This is very interesting. Granules in any conglomerate are several orders of magnitude bigger than molecules, so this suggests that the surrounding processes, playing the role of a re-scaled 'solvent' perhaps? replicate what molecules would do in a fluid, only re-scaled.

Does that imply something like landslides being pictured as some kind of re-scaled phase change similar to what the original post by @paulsutton seemed to imply?

When I say 'solvant' I include air, water, the vacuum... The vacuum is a solvant, as far as any of us should be concerned.

2 hours ago, joigus said:

This is very interesting. Granules in any conglomerate are several orders of magnitude bigger than molecules, so this suggests that the surrounding processes, playing the role of a re-scaled 'solvent' perhaps? replicate what molecules would do in a fluid, only re-scaled.

Does that imply something like landslides being pictured as some kind of re-scaled phase change similar to what the original post by @paulsutton seemed to imply?

When I say 'solvant' I include air, water, the vacuum... The vacuum is a solvant, as far as any of us should be concerned.

With landslides, I am not sure, I think with an avalance (snow) the snow moves on a pocket of air, does a land slde do the same thing, we have had several in Dorset where the cliffs have collapsed, I generally think of a landside as also when thereis lots of water causing mud, and other debris to move down hill taking things with it.

I was thinking this, as we can pour liquids and also pour a container of Sodium Chloride into a beaker, despite the latter being made of small (granular) particles.

With landslides, I usually think of these as being mostly caused by rain fall for example causing the ground to I guess to lose cohesion and move down a hillside or cliff face.

We have had this in Dorset,

https://www.bbc.co.uk/news/uk-england-dorset-68332305

However, I think these are caused by the area being very dry and collapsing (maybe weight related), the ground also cracks in very dry weather, ( probably the correct term is fissure )

Avalanches (IIRC) are moving snow but are these on top of a pocket of air or is there a sort of air pocket in front of the moving snow.

Does the shape of the particles also play a part, I think Salt (NaCl) is cuboid (or at least looking at the structure diagrams it is) graphite is layers so they slide, compared to diamond which is more ridged),

Sand appears to be trangular or perhaps pyramid shaped

https://chem.libretexts.org/Courses/Honolulu_Community_College/CHEM_100%3A_Chemistry_and_Society/14%3A_Earth/14.02%3A_Silicates_and_the_Shapes_of_Things

So maybe this is also a factor in how easy something will move around (even if sold).

Paul

41 minutes ago, paulsutton said:

With landslides, I usually think of these as being mostly caused by rain fall for example causing the ground to I guess to lose cohesion and move down a hillside or cliff face.

Gravity plays a big part though, somehow analogous to the high stress that the authors of the paper mentioned for the case of fluids.

3 hours ago, paulsutton said:

I was thinking this, as we can pour liquids and also pour a container of Sodium Chloride into a beaker, despite the latter being made of small (granular) particles.

With landslides, I usually think of these as being mostly caused by rain fall for example causing the ground to I guess to lose cohesion and move down a hillside or cliff face.

We have had this in Dorset,

https://www.bbc.co.uk/news/uk-england-dorset-68332305

However, I think these are caused by the area being very dry and collapsing (maybe weight related), the ground also cracks in very dry weather, ( probably the correct term is fissure )

Avalanches (IIRC) are moving snow but are these on top of a pocket of air or is there a sort of air pocket in front of the moving snow.

Does the shape of the particles also play a part, I think Salt (NaCl) is cuboid (or at least looking at the structure diagrams it is) graphite is layers so they slide, compared to diamond which is more ridged),

Sand appears to be trangular or perhaps pyramid shaped

https://chem.libretexts.org/Courses/Honolulu_Community_College/CHEM_100%3A_Chemistry_and_Society/14%3A_Earth/14.02%3A_Silicates_and_the_Shapes_of_Things

So maybe this is also a factor in how easy something will move around (even if sold).

Paul

If you want to understand all this, we need to start back 250 years before Christ, when a Greek gentleman made his famous utterance about Archimedes Principle.

The interesting thing is that the importance of AP, in this context, was not enunciated until after Relativity, after QM and after Godel in 1936 when Terzaghi introduced the notion of 'effective stress'.

So I am going to ask if you understand the notions of contact force, contact stress, and the classification into direct (also called normal) force and stress and (not indirect or abnormal) but tangential or shear force and shear stress,

Liquid mechanical behavious is controlled by shear stress, as is soil and rock mechanics in regard to failures such as landslip, avalanche, slope stability and so on.

Soils break due to shear failure in almost every case.

If you are not sure about any of the terms please ask and I will include the necessary explanations in my next post.

Conceptually it really is quite a simple subject ( mathematicians can always make it more hairy than it really needs to be)

1 hour ago, joigus said:

Gravity plays a big part though, somehow analogous to the high stress that the authors of the paper mentioned for the case of fluids.

High stress is just not necessary.

Did you manage to access the full paper by any chance ?

Edited Tuesday at 07:07 PM3 days by studiot

7 minutes ago, studiot said:

High stress is just not necessary.

Did you manage to access the full paper by any chance ?

Unfortunately, no.

I didn't say it was necessary though. It could be sufficient. It could be neither: only highly correlative statistically. But any illuminating comments on your part are very welcome.

Think of two large diameter pistons face to face, with a liquid film bond between them. Air pressure on the external surfaces opposes rapid separation.

If the pistons are drawn apart slowly, the fluid pinches in at the circumference and gradually separates from the edge to the centre with no velocity discontinuity. The growing space between the separated films is occupied by air.

As more separation force is applied exceeding the sum of external pressure and van der Waals, the interface begins separating faster than air can fill the space, forming a vacuum and velocity discontinuity followed by a bang as the air catches up.

Generally the pressure within the film will dip below its vapour pressure and boil a bit reducing the degree of banginess (basis of cavitation).

Certain non-Newtonian fluids will like crystalline solids, support significant negative pressures in tension with consequent increased 'banginess'.

All I'm really seeing here are the underlying physics of Water Hammer and Liquid Column Separation

Tensile behaviour of elastic fluids covers some of the more polymery associated behaviours.

22 hours ago, studiot said:

If you want to understand all this, we need to start back 250 years before Christ, when a Greek gentleman made his famous utterance about Archimedes Principle.

The interesting thing is that the importance of AP, in this context, was not enunciated until after Relativity, after QM and after Godel in 1936 when Terzaghi introduced the notion of 'effective stress'.

So I am going to ask if you understand the notions of contact force, contact stress, and the classification into direct (also called normal) force and stress and (not indirect or abnormal) but tangential or shear force and shear stress,

Liquid mechanical behavious is controlled by shear stress, as is soil and rock mechanics in regard to failures such as landslip, avalanche, slope stability and so on.

Soils break due to shear failure in almost every case.

If you are not sure about any of the terms please ask and I will include the necessary explanations in my next post.

Conceptually it really is quite a simple subject ( mathematicians can always make it more hairy than it really needs to be)

High stress is just not necessary.

Did you manage to access the full paper by any chance ?

I am not sure what some of these mean exactly, so alongside any explanation here, I am going to do my own digging and research them ( it is kinda expected here after all) it will be interesting to compare findings as they should be the same or very similar explanations ( if I find the right sources).

Paul

4 hours ago, paulsutton said:

I am not sure what some of these mean exactly, so alongside any explanation here, I am going to do my own digging and research them ( it is kinda expected here after all) it will be interesting to compare findings as they should be the same or very similar explanations ( if I find the right sources).

Paul

Since you didn't say which ones I am going to start at the beginning, but assume you have some intuitive idea as to what is meant by a force, commonly stated as a push or a pull.

This is a good start, about where Archimedes was coming from, but we need expanded detail for modern consideration.

The weight of an object is a force.
You can use that force to exert a push on something, by standing the object on it, say a brick on a table.
Or a pull on that something by hanging the object from it, by a string,
Or you can develop what is called a turning moment by pulling on one side or the other, tipping a wobbly table with a pile of bricks.
This third use of a force is not often included in the popular definition, but we will use it later as it is very important in landslips and soil failures.

Archimedes realised that the weight of an object is lessened by immersion in water, though it regains its original weight when removed from the water.
He had discovered what we now call the bouyancy force, which acts against the weight force of the object itself.
Though he didn't think of it in that way, in doing so he had discovered the idea of a net or resultant force.
This is what happen when two or more forces act on the same body.

I haven't the time tonight to do any sketches, so having set the scene I will continue tomorrow to extend Archimedes to Terzaghi's soil loading equation (Which is actually very simple).
We have also found out that we need to know more about how to apply a force and I will address that which will lead to the idea of stresses and strains.

How are we doing ?

Meanwhile if you watch the BBC Devon local website there is a short but good video of a landslide that occurred last weekend near Teighmouth.

https://www.bbc.co.uk/news/england/devon

19 hours ago, sethoflagos said:

Generally the pressure within the film will dip below its vapour pressure and boil a bit reducing the degree of banginess (basis of cavitation).

I was just thinking of cavitation, as in pumps or submarine screw propellers, which is capable of breaking impellers.
And loud enough togive away the position of the submarine to sonar.

16 hours ago, MigL said:

I was just thinking of cavitation, as in pumps or submarine screw propellers, which is capable of breaking impellers.
And loud enough togive away the position of the submarine to sonar.

Cavitation is also how to propel an object up to high speeds under water, just at the front instead of using the rear mounted propeller. To the OP; I must have missed something because the whole discussion about "fracturing" seems like semantics to me. When I do a cannonball into the swimming pool, isn't the resulting splash from water "fracturing"?

So to reply to @studiot I have tried to look up some of the terms / ideas presented above and put my thoughts / interpretations below along with references to where I got the explanation from.

* Archimedes Principle.

[Archimedes Principle.](https://www.britannica.com/science/Archimedes-principle) covers the laws of buoyancy and states that " that any body completely or partially submerged in a fluid (gas or liquid) at rest is acted upon by an upward, or buoyant, force,"* [1]

* Convert [Newtons to grams](https://www.convertunits.com/from/newton/to/gram)

* Terzaghi introduced the notion of 'effective stress'. [2]

If we apply this to sand then the sand, if placed in a heap (with a slope) needs to have enough strength to stop that slope moving (or as per [2]_ slumping. [2].

Comment, this makes sense, if you're on a beach and try and take the top layer of dry sand and pile this up, it is harder to create a pile, where as digging deeper to the sand that has more firmness (due to water content) can be dug out and piled up, the same goes for making sandcastles, they are likely to stand on their own if the sand is damp and sticks together, nevertheless if you use very wet sand you end up with a similar situation as with the dry sand, it won't keep it's shape.

* Contact force, [3]

These are forces between two objects

* Contact stress [4]

I don't fully understand this from reading the source I found. (Don't understand dwell pressure)

* Direct (also called normal) force and stress [5]

From the source (wikipedia)

"In continuum mechanics, stress is a physical quantity that describes forces present during deformation. For example, an object being pulled apart, such as a stretched elastic band, is subject to tensile stress and may undergo elongation. An object being pushed together, such as a crumpled sponge, is subject to compressive stress and may undergo shortening"

So I get this, so if I pull something it becomes longer, and I guess weaker as it becomes more elongated, going the other way the stress of compression can also impact.

* Tangential or shear force and shear stress ( not indirect or abnormal ), [6]

I think I get the principle behind this, so two objects moving against each other. I guess another example is to rip sheet of paper, by holding and pulling in opposite directions causing the paper to be pulled (ripped) apart.

Would I be right in thinking that if I try and bolt two materials together that are held in tension, the bolt must be strong enough (tensile strength) to resist the two forces pulling apart that the bolt is holding together.

References

1.[Archimedes Principle.](https://www.britannica.com/science/Archimedes-principle)

2 [33.2: Terzaghi's Effective Stress Principle](https://eng.libretexts.org/Bookshelves/Materials_Science/TLP_Library_I/33%3A_Granular_Materials/33.2%3A_Terzaghi's_Effective_Stress_Principle)

3 [Contact force](https://en.wikipedia.org/wiki/Contact_force)

4 [Contact Stress at the Beginning of Demolding[(https://www.sciencedirect.com/topics/engineering/contact-stress)

5 [Stress (mechanics)](https://en.wikipedia.org/wiki/Stress_(mechanics)) - This may not be the correct reference

6 [Shear forces](https://en.wikipedia.org/wiki/Shear_force)

Hope this helps

Paul

2 hours ago, npts2020 said:

Cavitation is also how to propel an object up to high speeds under water, just at the front instead of using the rear mounted propeller. To the OP; I must have missed something because the whole discussion about "fracturing" seems like semantics to me. When I do a cannonball into the swimming pool, isn't the resulting splash from water "fracturing"?

No. If you look at the picture this fracturing is a jagged break like that you get when a solid material fails.

2 hours ago, npts2020 said:

Cavitation is also how to propel an object up to high speeds under water

You're going to have to explain how you would accomplish that.

As far as I know, a known method to achieve high speed underwater, is to envelop a torpedo in a sheath of air; the opposite og cavitation.
Russians have experimented with such methods, using H₂O₂ to generate the sheath.
The Kursk ( Russian nuclear sub ) incident of 2000 in the Barents Sea, is attributed to high strength Peroxide leaking from a faulty weld, into the torpedo tube, catalyzing a fatal explosion.

Edited 23 hours ago23 hr by MigL

2 hours ago, paulsutton said:

So to reply to @studiot I have tried to look up some of the terms / ideas presented above and put my thoughts / interpretations below along with references to where I got the explanation from.

You have been busy, which is good, but I hope that all will be made clear in due course as we go along.

There are gaps and some slight misconceptions in what you have picked out so don't range too far ahead.

Unfortunately events today cut my good intentions rather short so I only got as far as sketching fig1, which describes Archimedes arrangement.

So Fig 1 describes Archimedes principle as you have found out. It shows a heavy (non floating) cubical block (that does not absorb water) dunked in a bucket of water.

But it also shows us a whole lot more if you know where to look.

A Force is defined to act along a particular line and at a particular point, known as the point of application.

This is demonstrated by the support rope providing the lift force.

The rope is attached to the block at a particular point on the top by a hook.

But

I have shown the bouyancy force as 'made up of' a lot of small forces spread over the whole base.

This is called pressure or a pressure force.

There is a rule that says all these little forces may be added up and replaced by one total combined force B, which does act along a single line.
Furthermore B acts upwards as shown, which leads to Archimedes equation.

Looking deeper we note that both the lifting force, L, and the bouyancy force, B, are external to the block.

Forces my be external or internal.

The application of external forces leads to internal forces.

We also see that both L and B are acting at right angles to the block.
Physicists have borrowed the mathematical term 'normal' to describe this right angle condition.

So L and B are normal external forces to the block.
Further L is a pull and B is a push.

There is also a rule that says that foces at right angles to a given force can have no effect on it.

There is always a direction at right angles to a normal force.
We will see in the next sketches how such forces at right angles to the normal act and learn that they are the forces of friction or shear, and how they work in principle.

We will also see how external forces in one body may be regarded as internal forces in another and how external forces generate internal forces.

Edited 22 hours ago22 hr by studiot

11 hours ago, exchemist said:

No. If you look at the picture this fracturing is a jagged break like that you get when a solid material fails.

I think the give away is that the OP reference fails to mention and distinguish their subject from Liquid Column Separation despite that being quite literally what they are describing. Of course, this doesn't prove they're the same thing, but then there'd have to be two phenomena the research team had never heard of.

AFAIK only Chem Eng give it any serious study time. The equations are non-analytic which puts off most but since it's very effective at straightening piping elbows etc we have to look at it. And who else would stick a waterfall in a pipeline?

3 hours ago, sethoflagos said:

I think the give away is that the OP reference fails to mention and distinguish their subject from Liquid Column Separation despite that being quite literally what they are describing. Of course, this doesn't prove they're the same thing, but then there'd have to be two phenomena the research team had never heard of.

AFAIK only Chem Eng give it any serious study time. The equations are non-analytic which puts off most but since it's very effective at straightening piping elbows etc we have to look at it. And who else would stick a waterfall in a pipeline?

As I understand this is either different from liquid column separation, or possibly a feature of the first instant after column separation, due to the nature of the “fractured” surface, which resembles a broken bitumen surface, i.e. not a smooth liquid phase surface.

3 hours ago, sethoflagos said:

I think the give away is that the OP reference fails to mention and distinguish their subject from Liquid Column Separation despite that being quite literally what they are describing. Of course, this doesn't prove they're the same thing, but then there'd have to be two phenomena the research team had never heard of.

AFAIK only Chem Eng give it any serious study time. The equations are non-analytic which puts off most but since it's very effective at straightening piping elbows etc we have to look at it. And who else would stick a waterfall in a pipeline?

This is why it is good to have a wide variety of backgrounds in the membership.

I would agree with exchemist that the photos in the original article would only be liquid column separation if they were of actually burst pipes.

But this is not at all clear.

This article is a good summary of our knowledge of LCS, including the equations Seth mentions.

https://www.researchgate.net/publication/228851496_Water_hammer_with_column_separation_a_review_of_research_in_the_twentieth_century

19 hours ago, MigL said:

You're going to have to explain how you would accomplish that.

As far as I know, a known method to achieve high speed underwater, is to envelop a torpedo in a sheath of air; the opposite og cavitation.
Russians have experimented with such methods, using H₂O₂ to generate the sheath.
The Kursk ( Russian nuclear sub ) incident of 2000 in the Barents Sea, is attributed to high strength Peroxide leaking from a faulty weld, into the torpedo tube, catalyzing a fatal explosion.

You just explained it. The cavitation (your "air sheath") takes place at the front, thus reducing drag close to that through air instead of through water resulting in higher speeds by almost an order of magnitude. The main limit for such a scheme is how fast the bubble in front can be made.

46 minutes ago, npts2020 said:

You just explained it. The cavitation (your "air sheath") takes place at the front, thus reducing drag close to that through air instead of through water resulting in higher speeds by almost an order of magnitude. The main limit for such a scheme is how fast the bubble in front can be made.

That’s not cavitation then. Cavitation involves generating a vacuum (strictly not quite due to vapour pressure of the liquid), from a surface moving too fast for the liquid to remain in contact with it, e.g. propeller, pump impeller. If you use air pressure to displace the liquid that isn’t cavitation.

Edited 3 hours ago3 hr by exchemist

6 hours ago, exchemist said:

As I understand this is either different from liquid column separation, or possibly a feature of the first instant after column separation, due to the nature of the “fractured” surface, which resembles a broken bitumen surface, i.e. not a smooth liquid phase surface.

I agree. Though I imagine that the freshly fractured water surfaces would be buried within a highly energetic aerosol mist that would be quite the reverse of smooth.

The polar opposite ratio of surface tension to viscosity makes bitumen less inclined to go as far as aerosol formation, and far less eager to revert so rapidly from rough to smooth.

The appropriate scaling factors (Laplace number, Bond number, Cavitation number, Ohnesorge number) span many orders of magnitude, so 'instant' is quite a relative concept.