Has An Important Property Of Fluids Been Overlooked ?

[minnie]

Hi Fletcher,
                this is really challenging. I'm hoping to come up with something, if I do I'll have to try and learn how to post
drawings, photos etc.
    I've got a son-in-law who's fairly conversant with these latest gadgets and I'm hoping he'll give me a bit of instruction
on how to post drawings and pictures.
  We get a bit of good, no-nonsense, farm equipment that's made in New Zealand, obviously you don't put `up with
too much junk over there!
            Keep up the good work,
                                                   John.

[fletcher]

Hi John .. just had my power restored after the cyclone here in Fiji, got wacked pretty bad but got off lightly compared to some - on holiday now till January.

I hope this last post for a while helps - it will make you scratch your head some more - but it has been my purpose to get people to think thru every step of hydrostatics & buoyancy & challenge statements - perhaps I was a bit optimistic that discussion would evolve openly & go forward without having to be telegraphed but you I'm sure will get some fun out of thinking about it & around it some more - it's really an interesting topic.


@ all ..

The usual fluids we consider are Newtonian fluids [water is one] - if this is the case then in my previous example it will not balance as is suggested - the reason is this - the masses [1 & 2, total 2 + 1 kgs = 3kgs] exert a pressure on the fluid in the filled container - they are met by an equal pressure from beneath - this means that the forces are equalized i.e. equilibrium - I'd call that buoyancy but you think of it any way you wish - at this stage the two masses have no turning moment around the pivot.

Now we consider the fluid under pressure - we do the calculations & we see that there is a total upthrust force & a total downthrust force - when the upthrust is subtracted from the downthrust we have a net downthrust of 420N [42kg] - this equals the fluid mass of 39kg plus the 3kg of the masses influence - this is hydrostatics - we can calculate the fluids Center of Pressure [CoP] by working backwards from the turning moments - we find that the CoP is thru the pivot i.e. balanced turning moments [except for the additional 1kg displacer].

The interesting thing about Newtonian fluids is that they have a CoM or CoG but is has no relevance - we are just interested in turning moments & CoP - solids on the other hand always use the CoM.

N.B. the Hydrostatic Paradox teaches us that the sum of the down forces minus the sum of the up forces will always equal the total fluid weight force, in either an open or completely closed system & in most cases the CoP will be located where the CoM is in regular shaped vessels - therefore if the solid displacer can be attached to a thin sealed shaft & weight beneath it it can sit on the bottom as seen or be surrounded by fluid when upside down & just be part of it.

The answer to the problem I suspected could be found in Non_Newtonian Fluids [see a couple of sites, they are very interesting] - in particular fluids that once pressure was applied changed their viscosity &/or their shearing stress also changed - there are many types of Non_Newtonian fluids, including pitch, clay slurry's, starches, suspensions of various sorts etc.

http://www.google.co.nz/search?source=ig&rlz=&q=for+viscous+fluids+stress+is+proportional+to+what+&oq=viscous+fluids&gs_l=igoogle.1.5.0l4j0i30l3j0i5i30l3.51.1118.0.20756.7.6.0.1.1.1.531.1229.2j1j2j5-1.6.0...0.0...1ac.1.AXuV80CeJek

http://en.wikipedia.org/wiki/Viscosity

http://en.wikipedia.org/wiki/Non-Newtonian_fluid

http://en.wikipedia.org/wiki/Maxwell_solid

Maxwell fluids have combination properties of both fluids & solids - I was rather hoping that for some Non-Newtonian fluid that it would have some hydrostatic properties in one mode & exhibit solid behaviour in another i.e. when under pressure the fluids CoM/CoG would take precedence rather than CoP, in which case the example, with the 1kg displacer, could work as per the sim because we used fluid CoM/CoG rather than CoP.

Have a good break.

P.S. the pantographs might come in handy if you want to rotate it.

[minnie]

Hi Fletcher,
                 some lesser minds may have deserted but I realised there was more to come. Some of the things you've been on about
haven't made any sense but hopefully something will emerge...............in the end!
  Anyone who's made custard from powder will know how fascinating a high viscosity material behaves.
I must admit I got rather "hooked" on mrwayne's fabulous machine and when that petered out I felt rather lost. Hence I started
following this thread. I'll no doubt be playing with/studying viscous materials for the next few days.
   Deep down I feel that a lot more must be done harvesting and storing the power of the sun, nearly all energy we use is of solar
origin, if only we could cut out the middle man!
                                                                      John.