Is it defying the law of Archimedes?

Discussion in 'Boat Design' started by sun, Jun 25, 2022.

  1. Alan Cattelliot
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    Alan Cattelliot Senior Member

    Or maybe the effects we can observe are so obvious that they distract us too much

    Floating on the water, or in the air could be considered already as a strong win against gravity.

    Water is denser than air... Water viscosity is greater than air... Two states of matter...

    Because our familiarity with water, we may have skipped important observations regarding its properties, its behaviour. Bernouilli or Navier-Stokes told us that we can learn from water observations some true statements also valid for the air (in conditions where gravitational effects may be neglected). So let's see a little more about water, to explore other views of how water produces forces and how is very electric nature makes it the perfect vessel to resist gravity. if you want to follow this talk :



    I like the idea of free energy. Compared to the energy needed to lift an aircraft by dynamical effects, the energy needed to float a watercraft is surely free... For now !
     
    Last edited: Jul 6, 2022
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  2. rnlock
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    rnlock Senior Member

    I don't want to get involved in the technical discussion here, but I thought I might post a couple more fun hydrofoil videos. Recommend sound off for the first one. It's got what you might call "marketing music", as if the visual part wasn't dramatic enough. Plus obnoxious play by play. But the boats are beautiful and amazing.

     
  3. gonzo
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    gonzo Senior Member

    Water does not produce forces. Forces may be applied to it and transferred by it though. I don't know what you mean by "electric nature", so you need to define the term; it is not in the scientific lexicon. Also, water is not a vessel, perfect or imperfect, and it does not resist gravity. Seems like you need to go back to basics and learn about the fundamentals for physics.
     
  4. TANSL
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    TANSL Senior Member

    Perhaps it is a question of nuances. Insofar as the weight of water could be considered as a force, it would be convenient to reconsider the affirmation that water does not produce forces.
    Water, in a hydroelectric plant, for example, produces forces that, in these times of gas scarcity, are very interesting.
     
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  5. Alan Cattelliot
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    Alan Cattelliot Senior Member

    I admit that my wording was more a kind of poetry than a true scientific statement. My mistake. If you could just replace the term "resist" by "oppose", it would make hopefully more sense.
    My purpose in using the word "vessel" was to draw the picture of a boat being held by the hydrostatic pressures, contrary to an airplane.
    that cannot hang in the air at zero speed ( Of course, "lighter than the air" crafts also use the buoyancy to navigate like watercrafts in water).Buyoancy is free, lift is not.
    Strictly speaking, tension forces at water interface are indeed true forces created by water itself, whose definitions do not need, nor the mass, nor the acceleration, to be fully expressed.
    IMG_20220728_215734.jpg
    Regarding the "electric nature of water", I will remind you that the H2O molecule is a polar molecule. As a result, depending on its orientation, water will exhibits a very characteristic spectrum that is used in astrophysics, for instance. This polarity is very important for the whole chemistry of our body, because the electric induced currents and the weak interactions resulting from this polarisation allows, for instance, exchange and recombination inside our cells.
    Gonzo, have you got a across the YouTube link I gave in my post ? After seeing this video, and with the background I have in Fundamental Physics (both nuclear and quantum, and molecular), I felt truly astonish by the electric properties of this EZ water, that is far beyond the very rough and classical approach that I've been taught about water being a very simple electric conductor.
     
    Last edited: Jul 28, 2022
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  6. gonzo
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    gonzo Senior Member

    Water is an insulator, not a conductor. Water with salts in solution will conduct electricity.

    Surface tension is a well understood phenomenon. Definition do need to be fully expressed, or there is no hope of having a meaningful discussion. Forces do not, ever, have mass. Depending on the frame of reference, forces are applied or are reaction forces.
     
  7. Alan Cattelliot
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    Alan Cattelliot Senior Member

    Yes Gonzo, thanks to recall that, and not to forget that any mineral impurities will have this kind of result, as soon as ion are present in the solution. Nevertheless, I wouldn't take a bath into an electrified distilled water, nor put anything in it, knowing that charges could ever come from the water container itself.
    I wish to push forward the reasonning about the notion of force. You've said it, our intuition of force comes with the idea of action and reaction. In Newton's theory, the equation F equal mass times the acceleration does give a clue about how we conceive this force. Although it does not really gives a clue of the nature of the Force itself in my opinion.
    Acceleration is just a definition, thus I guess we have nothing to say about it, do we ? Then what about the mass ?
    Do you believe gravity is a force ? What forces do you know that do not contain a mass in its definition ? Surface tension is one of them, what are the others ?
     
  8. gonzo
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    gonzo Senior Member

    Gravity is not a force, but an acceleration.
    There is no such this as "intuition of force". Force is a vector that can be measured and calculated.
    F=ma, gives more than a clue to the nature of force; it defines it.
     
  9. rnlock
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    rnlock Senior Member

    I guess you've never been hit by a snowball. ;-p
     
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  10. gonzo
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    gonzo Senior Member

    That is the force generated by the change in acceleration. Remember: F=ma
     
  11. rnlock
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    rnlock Senior Member

    You know, if you want, you can trace back all forces to the Big Bang, and say nothing after that actually created a force. Not very useful, I'd say. And not very funny either.
     
  12. gonzo
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    gonzo Senior Member

    If you can justify that statement, it would be the biggest advance in physics and the history of the Universe in a century.
     
  13. mitchgrunes
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    mitchgrunes Senior Member

    Hey guys, with such a simply worded question, you could answer more simply.

    Airplanes and "planing hull boats and ships" are pushed upwards because some of the air or water is pushed downwards. (Note: many boats and ships are "displacement hulls", especially at lower speeds, which actually push water at the front sideways, pushing it up into bow waves, so the net force at the front of the boat, which tends to dominate, is typically downwards.)

    The details of how that works can vary. I used to have a physics professor who claimed that wing lift diagrams based on Bernouli's principle were all wrong. E.g., Bernouli's principle, which is based on the idea that you have decreased pressure over the object, to the extant it is correct, probably implies that some of the air is pushed upwards - which means there would be a net downwards force.

    But airplane wings are also tilted upwards in front, during normal flight, which means that there is a stream of air behind the blade that is going somewhat downwards, because the complex airflow patterns around the wing direct the air that way, which means that the wing is pushed upwards. In other words, if the wing were flat and level, or symmetrical and level, there would be no lifting force.

    There is a principle in introductory physics classes called Newton's 3rd law, that says that in order to push something one way, something else must be pushed in the opposite direction. It can get more complex than that in more advanced classes, but for many basic mechanical problems, Newton's 3rd law is a good starting point.

    The actual details of how molecules move, to create all these forces, may be extremely complex and difficult to model, but the basic idea is simple.
     
  14. Barry
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    Barry Senior Member

    If water does not produce a force, please explain,

    I place a cup that has one pound of water in it on a scale, the scale reads one pound plus the weight of the cup, this is not a force you say?


    Similarly I take a garden hose and discharge it at a ball on the ground. The ball can only move with an application of force. While there is no doubt there is a force generated by the change of direction of water at the impact area,
    but it is only the water that is providing the force to accelerate the ball.
     

  15. Will Gilmore
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    Will Gilmore Senior Member

    What's the Definition of a Liquid in Chemistry? https://www.thoughtco.com/definition-of-liquid-604558
    What the Intermolecular Force Is in Chemistry https://www.thoughtco.com/definition-of-intermolecular-force-605252
     
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