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Author Topic: Displacement?  (Read 2676 times)

Martin [Admin]

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Displacement?
« on: January 12, 2013, 09:31:55 PM »


 Let me see if I understand displacement correctly....

 The Falkirk Wheel in Scotland is the weight of each gondola the same whether it has a boat in it or not?

 What if the boats are much heaver on one side?





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Colin Bishop

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Re: Displacement?
« Reply #1 on: January 12, 2013, 09:44:59 PM »

The boats will displace their weight in water Martin so there will be no difference.
 
Colin
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RAAArtyGunner

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Re: Displacement?
« Reply #2 on: January 12, 2013, 09:52:08 PM »

 
The Falkirk Wheel in Scotland is the weight of each gondola the same whether it has a boat in it or not? Yes


 
What if the boats are much heaver on one side? One should never guess and not being familiar with the 'wheel', however logic dictates that as they are both vessels and that  they both displace water relevant to their size, then resultant weight will be the same. They will be equal.
 
Couldn't see them building it if is was not so, as one side would then have a torsional load greater than the other.
 
There is visual evidence of the 'equality' as the 'lock' whilst being elevated/rotated remains level/horizontal with different sized vessels side by side.
 
Seems a reply from someone versed in Hydraulics is called for.
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Circlip

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Re: Displacement?
« Reply #3 on: January 12, 2013, 10:19:32 PM »

With no boats, only water in the gondolas, the weight is the same.
 
Put a 1 Ton (or tonne) displacement boat in one side and the water displaced is 1 Ton (or tonne) so the gondola still weighs the same as its mate.
 
  Similarly, if you put two boats in one gondola, whatever weight the second one displaces still holds the system in equilibrium.
 
  Surfice to say, according to the pundits, the electrical power needed to turn the "Wheel" is less than that required by a food mixer.
 
  Regards  Ian.
 
 The gondolas are kept horizontal cos the dam great gears on the ends rotate them within the arms.
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NFMike

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Re: Displacement?
« Reply #4 on: January 12, 2013, 10:38:05 PM »

This is the point where you say "eureka", Martin :-))

Circlip

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Re: Displacement?
« Reply #5 on: January 12, 2013, 10:45:35 PM »

Same applies to the canal lift that they copied from, the Anderton.
 
  Regards  Ian.
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Martin [Admin]

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Re: Displacement?
« Reply #6 on: January 13, 2013, 12:28:27 AM »


Right I accept that.... sort of!

Question 2:
I have an aqueduct, say 300m long,  35m wide, 12m deep.
The QE2, somehow, has to cross it, if she doesn't touch it - is my aqueduct in dander of collapsing?

 ( http://en.wikipedia.org/wiki/QE2 )


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dreadnought72

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Re: Displacement?
« Reply #7 on: January 13, 2013, 02:27:16 AM »

No - it won't collapse. 

Your aqueduct has about 126000 tonnes of water in it before the QE2 turns up. The QE2 (65000 tonnes?) will mean she'll displace that much water when she arrives, leaving the aqueduct with the QE2 and 61000 tonnes of water in it.

Think of it this way: imagine making a strong steel former exactly the size of the QE2's underwater hull, but a millimetre bigger in every dimension. Fill the former with water. Put in the QE2. She'll displace 65000 tonnes of that water, and be floating on a 1mm skin of what's left. She's as afloat in that millimetre as she would be in your aqueduct or over the Marianas Trench.

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slug

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Re: Displacement?
« Reply #8 on: January 13, 2013, 07:41:13 AM »

martin what a thought for sunday morning..the mind boggles,what happens to all the water that is displaced in the aquaduct....tony
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ardarossan

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Re: Displacement?
« Reply #9 on: January 13, 2013, 09:30:15 AM »


 Let me see if I understand displacement correctly....

 The Falkirk Wheel in Scotland is the weight of each gondola the same whether it has a boat in it or not?

 What if the boats are much heaver on one side?



Bear in mind that much of the physics occurred way before any of our different-sized boats arrived at the Falkirk Wheel (in this instance).
 
To clarify, a boat displaced the volume of water equivalent to it's own weight when it was first launched, and although it is displacing water all the time it remains submerged in it, all the boat is really doing is swapping places with it's own weight of water, as it moves through it.

Therefore, going back to the Falkirk Wheel, if a 7.641-ton boat (for example) goes into a gondola, it will push 7.641 tons of water out of the way.
The volume of displaced water (weighing 7.641 tons), will be equal to the amount of boat that is below the water surface.

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Colin Bishop

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Re: Displacement?
« Reply #10 on: January 13, 2013, 11:15:50 AM »

Martin,
 
The key point here is that when you introduce the boat an equivalent weight of water flows away because the ends of the aqueduct are open. It's not like when you get into the bath and the water level rises, floods the floor and drowns the cat in it's basket in the room below.
 
Colin
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dreadnought72

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Re: Displacement?
« Reply #11 on: January 13, 2013, 11:18:36 AM »

Ludicrous, Colin. ...One of my cats sits on the edge of the bath when I'm in it.  %)

Andy
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Circlip

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Re: Displacement?
« Reply #12 on: January 13, 2013, 01:02:59 PM »

But the theory that says "Cats always land on four feet" is rubbish, not on four feet of water they don't.  %)
 
  Regards  Ian.
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Martin [Admin]

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Re: Displacement?
« Reply #13 on: January 13, 2013, 02:39:51 PM »


Your right Colin, thinking about it, that's precisely where I've misguided myself!   

  Thanks! :-))
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Netleyned

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Re: Displacement?
« Reply #14 on: January 13, 2013, 02:51:44 PM »

Would a catamaran displace twice as much?
A trimaran thrice??
 :D :D 
BTW, To keep wear to a minimum and even it out,
the wheel changes direction after each complete
revolution. Clever Engineering

Ned
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NFMike

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Re: Displacement?
« Reply #15 on: January 13, 2013, 03:04:32 PM »

Martin,
 
The key point here is that when you introduce the boat an equivalent weight of water flows away because the ends of the aqueduct are open. It's not like when you get into the bath and the water level rises, floods the floor and drowns the cat in it's basket in the room below.
 
Colin

In fact the water level does rise when a ship or boat is launched, but the 'bath' is huge, so we don't notice.

But when the 'ship' is a big chunk of Antarctic ice we will notice :)
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