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Re: Why does a less dense object rise in a dense fluid surrounding?

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<poraty6@gmail.com> wrote:
> On Friday, January 11, 2019 at 6:21:03 PM UTC+2, Odd Bodkin wrote:
>> benj <benj.fake@gmail.com> wrote:
>>> On 1/10/2019 2:14 PM, Odd Bodkin wrote:
>>>> benj <benj.fake@gmail.com> wrote:
>>>>> On 1/10/2019 8:00 AM, Odd Bodkin wrote:
>>>>>> Arindam Banerjee <banerjeeadda1234@gmail.com> wrote:
>>>>>>> On Earth. Why does a less dense object rise up in a dense fluid surrounding medium?
>>>>>> 
>>>>>> Because the weight of the object is less than the buoyant force of the
>>>>>> fluid, which in turn is due the differential in pressure with depth of the
>>>>>> surrounding fluid. High school physics.
>>>>> 
>>>>> Babbling jargon. Try explaining something in English for a change if you
>>>>> can understand things well enough. You are one of those WEstern Idiot
>>>>> dogs that Banjoji is always talking about.
>>>> 
>>>> Im a little surprised you find this jargon. Lets suppose that everyone
>>>> here knows what pressure is and what a fluid is. It is common experience
>>>> that pressure increases linearly with the depth in a fluid, in cases where
>>>> the density of the fluid is approximately constant. Anyone that has
>>>> snorkeled knows this. The pressure on any patch is in fact the weight of
>>>> the fluid sitting on top of that patch.
>>>> 
>>>> To make this visually clearer, consider first a pool of water, and imagine
>>>> an upright cylindrical volume of this water. If it helps, wrap this volume
>>>> in a thin cylindrical can made of plastic of the same density as the water,
>>>> so that it has no effect on the following. There is pressure inwards on the
>>>> outside of this cylinder due to water pressure. From symmetry, the force on
>>>> the left side of the can balances the force on the right side of the can,
>>>> at any given depth. But the pressure increases with depth, so the pressure
>>>> in the flat top surface of the can is different than the pressure on the
>>>> flat bottom surface of the can. The net force exerted by the fluid outside
>>>> the can is just then the difference in the forces on top and bottom of the
>>>> can. This is called the buoyant force of the fluid on the can. Since the
>>>> pressure on the bottom of the can is greater than in the top, the buoyant
>>>> force is upward.
>>>> 
>>>> This volume of water (with or without the can) is obviously in equilibrium.
>>>> It moves neither up nor down. Thus the downward force of gravity on that
>>>> volume of water (namely its weight) is therefore balanced by the upward
>>>> buoyant force. This is the statement of Archimedes Principle, that the
>>>> buoyant force is equal to the weight of the fluid displaced.
>>>> 
>>>> Quantitatively, the weight of the water inside the can is the mass times
>>>> the acceleration of gravity. The mass of the water is the density times the
>>>> volume. If our van has ends of area A and the top of the can is at depth d1
>>>> and the bottom is at depth d2, then the volume of the can is A * (d2-d1),
>>>> and thus the weight of the water displaced is (density)*A*(d2-d1)*g. We
>>>> just said this is equal to the buoyant force (Archimedes principle), and
>>>> we said earlier that this was due to the difference in water pressure on
>>>> the top and bottom of the can. This is obviously satisfied if the pressure
>>>> (force per area) on the top is (density)*d1*g and the pressure on the
>>>> bottom is (density)*d2*g. This is the source of our earlier statement that
>>>> the pressure increases linearly with the depth in the fluid.
>>>> 
>>>> As the last step in thinking this through, replace the contents of the can
>>>> with some substance other than water. The pressure from the fluid OUTSIDE
>>>> the can doesnt change  it doesnt care whats inside the can. So the
>>>> buoyant force is still the same, equal to the weight of the water displaced
>>>> by the can. But the weight of the contents of the can has changed. If the
>>>> can is filled with styrofoam, the weight of the contents is now smaller,
>>>> and the buoyant force is relatively bigger, and so there is a net force
>>>> upward and the can filled with styrofoam rises. If the can is filled with
>>>> birdshot, the weight of the can contents is now larger than the buoyant
>>>> force, and thus can will sink.
>>>> 
>>>> This is high school physics.
>>> 
>>> then why are you having so much trouble explaining it in words?
>>> 
>>>>>>> So exactly why does a cork bounce up when submerged in water?
>>>>>>> If the top of a hot air balloon was pointy instead of flat would it rise?
>>> 
>>> Fact is I looked in the index in a number of College Freshman physics 
>>> texts and none of them had the term "buoyant force" listed. 
>> 
>> Well, Im not sure what ones you looked at. First three I pulled from my
>> shelf sampled different vintages: 
>> 
>> Halliday & Resnick (1977) pg 376
>> 
>> Giancoli (2000) pg 340-343
>> 
>> Mazur (2015) pg 469-471
>> 
>> Buoyant force called out (and carefully defined) there.
>> 
>> 
>>> Mostly they 
>>> only mentioned in passing that under Archimedes principle, objects in 
>>> fluid are "bouyed up". It's interesting that while you try to explain 
>>> what is going on with words, you can't. You lapse into equations and 
>>> jargon and end up chasing your own tail over and over.
>> 
>> Physics is a quantitative science. I added a paragraph about how to do
>> things quantitatively because its important to do so in physics. It also
>> served to justify the claim of linear dependence between pressure and depth
>> in a constant-density fluid. 
>> 
>>> 
>>> You don't explain any general situation at all 
>> 
>> Nor was that asked for. The question was Why does a less dense object rise
>> in a dense fluid surrounding? 
>> 
>> Which I answered. 
>> 
>>> and then trying to use a 
>>> single restricted example of a cylindrical "can" you don't even cover 
>>> that case reasonably. if the can rises out of the liquid how does it 
>>> have a force on it's top cover? 
>> 
>> Im glad you asked! Thats an elaboration that can be easily explained in
>> much the same way. 
>> 
>> First note that the shape of the can doesnt matter. The very same
>> arguments I used for a cylinder would also apply to a rectangular block,
>> for instance. One can also see that an assemblage of two stacked cylinders
>> or stacked rectangular blocks yields the same result. By extension, even
>> the same result can be found for a cone, either point up or point down, by
>> approximating it with a stack of concentric cylinders of different radii.
>> This last point also shows that the orientation of the shape doesnt
>> matter. Thus we conclude that Archimedes principle applies regardless of
>> the submerged shape or orientation. Indeed, the story of Archimedes
>> revelation had to do with a crown, quite a complicated shape. 
>> 
>> If the buoyant force is greater than the weight of the object, then it will
>> rise to the surface. At this point, neither the buoyant force nor the
>> weight have changed, so it will continue to rise so that some portion of
>> the body is above the fluid. When that happens, the amount of the fluid
>> displaced starts to drop, and so the buoyant force also drops (see
>> Archimedes principle). When the weight equals the buoyant force, then it
>> will be in equilibrium again. 
>> 
>> There are many applications that could be discussed here, over many many
>> pages of additional, plain English prose. 
>> 
>>> Does the principle quit working them? Of 
>>> course it still works. And even worse you don't even mention the problem 
>>> that the can might flip over. Why? What are the conditions that control 
>>> this?
>>> 
>>> Sylvia did much better than you on this. Maybe you should ahs Sylvia for 
>>> some science lessons.
>>> 
>>> So If I take your mythical "can" and fill it completely with water 
>>> sealed with it's lid and then toss it into a pond, will it sink or 
>>> float? And if it floats in which orientation will it float? Explain 
>>> using words with no math, please. This is high school physics.
>>> al
> 
> e ===========================================much simpler 
> 
> and less    compose ass !!
> things are ***moving from more dense environment
> to less dance    one**!

And WHY? 

Or are things just willful about needing room?

> 
> there  is always inner   motion of particles   and objects  !!!!!
> IN ALL   DIRECTINS (automatic   test )take for instance a  metaphor example
> imitating the above situation
> 
> 
> 
>  you**  are in a dense crowded place 
> and looking how to get   off it!!
>  
> looking   in   all  possible   directions 
> than at last 
> you see a direction in which it will look/
> and not less ''feel' !!!!it will be the   easiest  
> directions  to   escape it 
> and bingo!!
> there you  ''chose '   your way out !!!!
> (automatic not automatic 
> call    it as you like it 
> nature as well   has that   ''wisdom !!!
> 
> ======================TIA
> Y.P
> =================
>  
> 
> 



-- 
Odd Bodkin — Maker of fine toys, tools, tables

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Thread

Why does a less dense object rise in a dense fluid surrounding? Arindam Banerjee <banerjeeadda1234@gmail.com> - 2019-01-09 21:12 -0800
  Re: Why does a less dense object rise in a dense fluid surrounding? Sylvia Else <sylvia@email.invalid> - 2019-01-10 23:20 +1100
    Re: Why does a less dense object rise in a dense fluid surrounding? Arindam Banerjee <banerjeeadda1234@gmail.com> - 2019-01-10 05:10 -0800
      Re: Why does a less dense object rise in a dense fluid surrounding? Odd Bodkin <bodkinodd@gmail.com> - 2019-01-10 13:32 +0000
        Re: Why does a less dense object rise in a dense fluid surrounding? benj <benj.fake@gmail.com> - 2019-01-10 13:13 -0500
      Re: Why does a less dense object rise in a dense fluid surrounding? Sylvia Else <sylvia@email.invalid> - 2019-01-13 16:31 +1100
    Re: Why does a less dense object rise in a dense fluid surrounding? poraty6@gmail.com - 2019-01-10 16:11 -0800
  Re: Why does a less dense object rise in a dense fluid surrounding? Odd Bodkin <bodkinodd@gmail.com> - 2019-01-10 13:00 +0000
    Re: Why does a less dense object rise in a dense fluid surrounding? Arindam Banerjee <banerjeeadda1234@gmail.com> - 2019-01-10 05:04 -0800
      Re: Why does a less dense object rise in a dense fluid surrounding? benj <benj.fake@gmail.com> - 2019-01-10 13:12 -0500
    Re: Why does a less dense object rise in a dense fluid surrounding? benj <benj.fake@gmail.com> - 2019-01-10 13:11 -0500
      Re: Why does a less dense object rise in a dense fluid surrounding? Odd Bodkin <bodkinodd@gmail.com> - 2019-01-10 19:14 +0000
        Re: Why does a less dense object rise in a dense fluid surrounding? "reber G=emc^2" <herbertglazier0@gmail.com> - 2019-01-10 12:28 -0800
          Re: Why does a less dense object rise in a dense fluid surrounding? benj <benj.fake@gmail.com> - 2019-01-10 19:36 -0500
            Re: Why does a less dense object rise in a dense fluid surrounding? "reber G=emc^2" <herbertglazier0@gmail.com> - 2019-01-11 09:40 -0800
        Re: Why does a less dense object rise in a dense fluid surrounding? mitchrae3323@gmail.com - 2019-01-10 13:21 -0800
        Re: Why does a less dense object rise in a dense fluid surrounding? benj <benj.fake@gmail.com> - 2019-01-10 19:32 -0500
          Re: Why does a less dense object rise in a dense fluid surrounding? Odd Bodkin <bodkinodd@gmail.com> - 2019-01-11 16:20 +0000
            Re: Why does a less dense object rise in a dense fluid surrounding? poraty6@gmail.com - 2019-01-12 23:56 -0800
              Re: Why does a less dense object rise in a dense fluid surrounding? Odd Bodkin <bodkinodd@gmail.com> - 2019-01-13 12:40 +0000
                Re: Why does a less dense object rise in a dense fluid surrounding? poraty6@gmail.com - 2019-01-13 16:01 -0800
    Re: Why does a less dense object rise in a dense fluid surrounding? poraty6@gmail.com - 2019-01-10 16:13 -0800
  Re: Why does a less dense object rise in a dense fluid surrounding? mitchrae3323@gmail.com - 2019-01-10 10:46 -0800
    Re: Why does a less dense object rise in a dense fluid surrounding? Sergio <invalid@invalid.com> - 2019-01-13 15:40 -0600

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