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Author Topic: The weight of things..........  (Read 7550 times)

polaris

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Re: The weight of things..........
« Reply #25 on: January 06, 2009, 06:18:39 pm »


Dear Malcolm,

All suitably deep outside test water is under three inches of ice! {:-{ Will however ask a physicist colleague/friend for opinion - specialises in fluid flow and all things elec. (his Father was a scientist in Germany during WW2 and was thankfully one of the few bagged by us and not the Americans! - the latter being somewhat very focused on rockets they missed quite a few other very important people in gnrl. science! :-))).

Regards, Bernard
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polaris

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Re: The weight of things..........
« Reply #26 on: January 06, 2009, 06:24:47 pm »


p.s. My last, the equation of line v. lifting weight is one of the important factors in lifting weights through mine shafts. You might have a cage weighing ten tons, but a mile down the 'rope' might weigh 30 or so tons! The 'rope' being in graduations of diameter to reduce overall winding weight... the 'rope' needs to be strongest nearer the top when at full extension obviously... just a further bit of gnrl. interest info.! B.
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Reade Models

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Re: The weight of things..........
« Reply #27 on: January 06, 2009, 06:45:44 pm »

Before slack rope detector switches were introduced on South African gold mines (my home turf) the weight of shaft ropes was responsible for almost as many deaths in the gold mining industry as rock bursts.

Occasionally a cage would jam in a shaft, but the winder would continue paying out rope until the jammed cage couldn't bear the extra weight of rope on its roof any longer.  The cage would suddenly break free and go hurtling down the shaft to a certain death for all of the occupants.

We used to drop test 1000KVA transformers. We knew from experience that you could roll a transformer into a cage at ground level (on a short rope) without any problem.  Take the cage down 3.5 Kilometers and try rolling the transformer out onto the landing - as the weight of the transformer transferred from the cage to the landing, the cage would shoot back up the shaft as the rope contracted neatly 'flipping' the transformer through a couple of somersaults before it landed (usually upside down).  Needless to say, we were all very adept at keeping out of the way...

Malc


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malcolmfrary

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Re: The weight of things..........
« Reply #28 on: January 06, 2009, 06:51:52 pm »

My lake is similarly afflicted, but an enquiring mind should direct itself to either a hammer, or, for the more scientific, a bucket of water indoors.
For a suggested use of a tapered rope, have a read of "Fountains of Paradise" by Arthur C Clarke (inventor of the communication satellite so we are told)
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polaris

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Re: The weight of things..........
« Reply #29 on: January 06, 2009, 06:56:00 pm »


Dear Malc,

Good to see another mining man on here! Thought I was alone! Hope you found the blasting pics. of interest? Have refrained from Posting more.

Regards, Bernard
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polaris

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Re: The weight of things..........
« Reply #30 on: January 06, 2009, 07:09:19 pm »


Dear Malc,

Re hammer and ice, have enough to do without going to such extremes! ;D :} There are much warmer ways of doing things! :-)) As to a bucket of water: done this years ago, and it never proved anything!

Regards, Bernard
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Reade Models

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Re: The weight of things..........
« Reply #31 on: January 06, 2009, 07:56:12 pm »

Dear Malc,
Good to see another mining man on here! Thought I was alone! Hope you found the blasting pics. of interest? Have refrained from Posting more.
Regards, Bernard

Hi Bernard

I'm not sure if I've seen the blasting pics?  Were they opencast?  I used to work for Johannesburg Consolidated Investments, part of Anglo American, first off on Platinum mines in the Rustenburg/Thabazimbi area, then later on shallow coal mines at Witbank and on deep level gold mines, Randfontien Estates and Western Areas - my only opencast experience was with drag lines on the highveld coal mines, though I was involved at Palabora Mine near Phalaborwa (on the edge of the Kruger Park) with open pit mining of copper ore for RTZ.  Plenty of blasting there! We had a herd of elephant resident on the plant, leopards too.  A group of baboons used to ride the run of mine conveyor sitting one behind the other - hilarious!

A world away from my life now....(Google Earth coordinates below).

Malc

  2359'30.75"S
  31 7'34.08"E

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polaris

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Re: The weight of things..........
« Reply #32 on: January 06, 2009, 09:23:48 pm »


Dear Malc,

Blasting links at end of Post. I partic. like the Glory Hole rounds.

You have been about! JCI good Co. to be with - good old BarneyB! Did a bit of cons. with CG and DeB, and later a some for INCO, followed by gen. with 'privates'. Had my own opers., but not on that scale! - all in a prev. life now! - still miss it now and again <:( - but much less stress these days :}! Was a C. of IMM until the IoM3 came along, now still C. with Iom3 but no fees now!!! - quite happy with this as would not otherwise be worth the fees - the latter now only a mere shadow of IMM as you know.

We have seen a few Baboons sitting on moving surfaces etc. over the years haven't we!!!!!!!!!!!!!!!!!! O0 :}  - all heading the same way as well!!!!!!!!!!! {-) %% Have lot's of fond memories!!!!!!!!!!  ;) LOL!!! {-)

Hope you like the Links... technically I like the Glory Hole rounds - mind you, there are some extreme cases of v.high tech. competence amongst this lot.

Regards, Bernard

http://uk.youtube.com/watch?v=xHldEwMvY70&feature=related

http://uk.youtube.com/watch?v=44tm26Fhqr8&feature=related

http://uk.youtube.com/watch?v=9DmUitYmxIM&feature=related

http://uk.youtube.com/watch?v=XM2TbddOhN0&feature=related

http://uk.youtube.com/watch?v=G4z-xUdroys&feature=related

http://uk.youtube.com/watch?v=G4z-xUdroys
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Reade Models

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Re: The weight of things..........
« Reply #33 on: January 06, 2009, 09:54:03 pm »

Hi Bernard

Do you know, if I had half a chance, I'd be back on the plane tomorrow...

Great blast video's - you wouldn't want to be anywhere close to that lot!  I particularly like the coal dust fireball - I keep harping on about the dangers of dust explosions in safety meetings, It's a bit like talking to a brick wall, you don't appreciate what can happen  unless you have first hand experience, but that video is a great example...

Malc



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polaris

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Re: The weight of things..........
« Reply #34 on: January 06, 2009, 10:05:58 pm »


Dear Malc,

Know what you mean. But, you know, I am pleased in numerous ways to be out of it now... things are so different these days. The rapid advance of tech. means that one would have to be v.more on ones toes now than before... it was bad enough then! %% - but somehow easier.

Re dust. It has been a 'thing' of mine for many years since I have asthma (not what they gen. call it now, but the hereditary type), and dust and fumes in working environs. always does for me so I am partic. tuned to the prob.. Hope that partic. footage might be of use to you then.

Regards, Bernard
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dreadnought72

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Re: The weight of things..........
« Reply #35 on: January 07, 2009, 09:48:17 am »

My lake is similarly afflicted, but an enquiring mind should direct itself to either a hammer, or, for the more scientific, a bucket of water indoors.
:-)

The easiest way to think about this is to consider balloons. Helium or hot air, they displace air equal to their volume. If the mass of the balloon is less than that of the mass of the air they displace, they'll rise until they reach a point where the masses are equal.

Ships work in the same way. If a hull is too high in the water, it'll sink; too low in the water, it'll rise. When it's found its level, the volume of water displaced masses the same as that of the ship.

A solid lump of metal submerged in water similarly displaces a volume equal to itself - so the (land weighed) 7800kg cubic metre of steel WILL weigh 6800kg in fresh water. (And, to be pedantic, it would weigh about 7801.2 kg in a vacuum, since a cubic metre of air masses around 1.2kg.)

There's a section in Das Boot, I think, where they trim the sub to "hang" via the periscope - effectively making it a surface vessel, albeit one with a minimal hull-above-water.

For a suggested use of a tapered rope, have a read of "Fountains of Paradise" by Arthur C Clarke (inventor of the communication satellite so we are told)
An excellent example of tapering. The wiki article on the cables required for orbital towers is a good read.

Andy #1963#
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Max Power

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Re: The weight of things..........
« Reply #36 on: January 07, 2009, 10:57:39 am »



Dreadnought said "If a hull is too high in the water, it'll sink; too low in the water, it'll rise. When it's found its level, the volume of water displaced masses the same as that of the ship."

This is obviously correct. Consider the case of a floating vessel with a pool of water contained within the hull. If the pool of water is drained the buoyancy of the vessel will increase and the vessel will rise in the water. This is true even if there were an object floating in the pool before it was drained and even if that object were another ship. This obviously applies to the scenario posed in the original post.

Consider the case in the original post. At the instant of closing the sea doors in the larger ship it must contain not only the 150T vessel but the 150Ton water required to float it. As the water is pumped out the buoyancy of the vessel increases by 150T and, as Dreadnought pointed out, it will rise in the water.
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polaris

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Re: The weight of things..........
« Reply #37 on: January 07, 2009, 11:02:58 am »


Dear Andy,

Thankyou for your Post. Interesting and quite right.

I have just this moment come off the phone with my physicist friend (recently retired Lecturer/Research Physicist, now doing geophysics research consultancy) - opportune as the Univ. goes back tomorrow so bagged him at home! As usual when asking a tech. question/query of him, I had the normal fascinating and invaluable Lecture... so, what was intended to be only a five minute call lasted over half an hour! - enjoyed every minute!

As you and Malc(Fray) point out, the weight does indeed decrease the further a weight is immersed in water, and once fully immersed, any given weight is indeed proportionately less. This applies whether the weight is on the seabed or suspended in water, since displacement is pertinent whatever be the case. Gravity plays it's part in giving all/everything it's weight obviously, so one must be careful in measuring such an experiment since there are gravitational differences (local and gen.), around the planet - only small of course, but would affect fine measurement all the same, and need computations done to adjust for localised gravitational variances. This is all a bit OTT for our purposes I suppose, but if we are talking about it we may as well get it all as 'right' as poss.! - similarly as your interesting Post.

Horst raised other 'sideline' factors, this being that the 'power' needed to 'accelerate' 1 ton(shift, drag, or move), would be proportionately the same anywhere - whether on the moon, underwater, or anywhere else. This all down to mass and gravity equations. There is obviously more to this, and I have a page of notes from the conv. and my mind is buzzing trying to remember other things he said... but I think we have gone into fine techs. far enough now!!! O0 :} - and I must do some work this am.!!! :((

As to my 'ship-in-ship' thing, he saw something else against it connected with the 'free water' within, so I am going away to think on this when-&-as over the coming months!!!

Thankyou to all who have taken the time to participate - certainly helped blow away the Festive cobwebs!!!!!!

Regards, Bernard
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tigertiger

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Re: The weight of things..........
« Reply #38 on: January 07, 2009, 11:17:33 am »

This thread is way over my head.

I can think of a simple solution to the problem.

Get a washing up bowl and fill it with water.

Take a buoyant object that will fit in washing up bowl. Weigh it, it needs to be fairly heavy.


Take a good set of scales. Digital bathroom at least. Weigh the bowl and water. Then insert boyant object.

What does it weigh now.

Then work out why.
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polaris

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Re: The weight of things..........
« Reply #39 on: January 07, 2009, 11:18:46 am »


Dear Max,

Thankyou for your Post.

But if the water is not pumped out, and the vessel within is floating on same, and the water within is still kept freely open to the level of the outside water, the weight of the inside vessel is still floating, BUT, the water within still has to be moved. How much vol. of water within the mother vessel for the within vessel to float in/on is important, since it must still be physically moved - even if the within vessel were only floating on/in six feet of clearance 'all round'. As I mentioned before, the idea is relatively ok while in calm weather/water, but not so good in rough conditions!

I must go and do some work now!!!!!!!!!! :((

Regards, Bernard
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polaris

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Re: The weight of things..........
« Reply #40 on: January 07, 2009, 11:20:02 am »


Dear Tiger,

Quite right.

Regards, Bernard
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malcolmfrary

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Re: The weight of things..........
« Reply #41 on: January 07, 2009, 01:22:13 pm »

Hi Tiger
You have described my idea of laboratory conditions - indoors and warm.  Working outdoors in the winter of 61-62 was a great incentive to staying awake on day release and trying to ensure an indoors job with minimal heavy lifting.
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Max Power

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Re: The weight of things..........
« Reply #42 on: January 07, 2009, 02:33:54 pm »


Dear Max,

Thankyou for your Post.

But if the water is not pumped out, and the vessel within is floating on same, and the water within is still kept freely open to the level of the outside water, the weight of the inside vessel is still floating, BUT, the water within still has to be moved. How much vol. of water within the mother vessel for the within vessel to float in/on is important, since it must still be physically moved - even if the within vessel were only floating on/in six feet of clearance 'all round'. As I mentioned before, the idea is relatively ok while in calm weather/water, but not so good in rough conditions!

I must go and do some work now!!!!!!!!!! :((

Regards, Bernard

I assume that the 20T weight of the mother ship refers to its unladen dry weight, (the sum of the weight of all its component parts out of the water). When in the water and containing a 150T vessel floating inside the hull, even when open to the sea, the space for the internal vessel must accommodate both the 150 ton vessel and in excess of 150 tons of water. In order for this to happen the "20T" mother ship will have to be ballasted so that it sits lower in the water. This ballast will have to be in excess of 300T! Without the ballast it would not be able to carry out the task.

So far as the mother ship moving through the sea with the smaller vessel still floating, this would not be a good idea. Once the mother vessel was moving at a steady speed everything would be fine; but accelerating up to speed, slowing down and turning would be cause problems. The internal floating vessel would crash into the sides of the containment space, unless it was very firmly moored, and the water would slosh about quite a bit.

We ourselves have the effects of inertia ably demonstrated to us if we are unfortunate enough to be standing up in a bus when it brakes {-)
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dreadnought72

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Re: The weight of things..........
« Reply #43 on: January 07, 2009, 03:48:14 pm »

... if we are unfortunate enough to be standing up in a bus when it brakes {-)

Which has to be the perfect point for me to link to this famous Billy Connolly routine. (Warnings for language and all the rest of it to those who might be offended by such things...)

Andy #1963#
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polaris

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Re: The weight of things..........
« Reply #44 on: January 07, 2009, 05:55:26 pm »


Dear Max,

You see, my idea is that the mother vessel is only a 'ship' in that it would only be 'acting' as one. The whole idea is that it is simply a powered containment: it need not necessarily have a bottom as one is not really needed other than to give support to the whole structure. The bottom would, if one was used, be deep in draft to enable other ships within. Ok, I hear people ask, what keeps all this afloat... easy, float modules along the sides since in theory it only needs to support it's own weight - again, the weight within is floating. Ballast would only be needed to 'balance' the mother vessel structure and not the vessel within - which is free floating. As has already been mentioned, the front loading doors present all sorts of tech. probs.. Yes things would move inside, but as I said prev., it all depends on how much internal water space is allowed. As someone else mentioned before, the mother ship is basically acting as a deep sea tug.

I think I might have to build a model!

Regards, Bernard
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Bryan Young

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Re: The weight of things..........
« Reply #45 on: January 07, 2009, 07:08:17 pm »

Another subject to ponder. My first pondering was as to why the question was asked in the first place. As it seems to be a bit of a no-brainer to start with, why all the exotic explanations? A little tinkling of thought would surely have equated total weight, mass, free flooding,deadweight and so on into one coherent "Eureka" moment. No? Oh, dear. How sad, but never mind. Another weird notion will pop up soon I'm sure. Cheers. BY.
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polaris

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Re: The weight of things..........
« Reply #46 on: January 08, 2009, 09:32:28 am »


Dear Bryan,

Quick note before going out.

To get different perspective and new views by throwing the subject to debate... to be afraid of putting an idea forward and not doing so is not conducive to invention.

Regards, Bernard
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Bryan Young

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Re: The weight of things..........
« Reply #47 on: January 08, 2009, 04:04:24 pm »


Dear Bryan,

Quick note before going out.

To get different perspective and new views by throwing the subject to debate... to be afraid of putting an idea forward and not doing so is not conducive to invention.

Regards, Bernard
No offence intended, and to be honest the debate is (was) sort of interesting. The original question was quite straightforward, but the brainpower that went into some of the replies made the subject more difficult than the question! Reminded me of the silly answers to the "wrong way round" steering as seen in the "Titanic" film. Keep up the lateral thinking...makes the world go around in a slightly better way. BY.
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polaris

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Re: The weight of things..........
« Reply #48 on: January 08, 2009, 05:57:09 pm »


Dear Bryan,

Thankyou for your Post. None taken.

"...but the brainpower that went into some of the replies made the subject more difficult than the question!...". How many times have I seen this happen over the years! O0 - the 'posed more questions than answers' syndrome!!! :-)) - like that situation as it shows something 'exists', as opposed to definitely doesn't! :-) The trouble is the original question was relatively straight forward, but, inevitably, it was bound to become more difficult as the subject enlarged. Ok, I had to explain the gnrl. idea a few times (all with slight difference), but each time this happen it obviously expanded things that bit further. However, the circle has been done, and thinking can be more straight line now.

Regards, Bernard

(If anyone new reads this and wants to reply, please read all the Posts as we don't want to go over anything already gone over! :-))

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