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 Sunday at 10:53 PM1 day 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.