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Yes, I think that is why they have a speed restriction when going over them.
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- Thread starter noseall
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No, because when the boat enters the canal, it displaces water of exactly the same weight.
If the aqueduct held 1000 tons of water, and you put a 10 ton boat in it, it now contains 990 tons of water and ten tons of boat.
Somebody is trying to make you think that the speed of the vessel causes extra water to be created.
It doesn't.
It just pushes it around a bit.
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If the water is lost to the canal system and everything it is connected to, then yes.
If not, then it would be different.
That will be the eventual outcome. What isn't clear is how long it takes to happen. The barge enters a very constricted channel. What happens to the water it displaces. Is it pushed forward, sideways, backwards or in all directions. How long does it takes for the displaced water to leave the aqueduct and merge with the rest of the canal at either end. Is it a fraction of a second, seconds, minutes, an hour or more?
The water level in the canal is managed, to prevent it overflowing.
The boat was in the canal before it entered the aqueduct.
It is still in the canal when it is in the aqueduct
It is still in the canal when it exits the aqueduct.
The weight of water plus boats in the canal and in the aqueduct does not change according to the speed of the boats.
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I don't disagree, but it does depend on whether the water that is displaced, when the boat enters the canal, is lost to the system or not.
If it is simply about a barge crossing a viaduct then, no, it won't affect anything.
It still has a 1000 tons of water plus the boat, less any water that splashes over the sides or gets forced out at either end
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If the water is distributed evenly in the system so will the mass. It doesn't matter where the floating barge sits, its mass is distributed evenly by the water. It the water isn't, it isn't, it's that simple. If the canal was long/large enough to suffer from tidal forces, the same would apply. The end with high tide would hold more water and therefore greater mass than the end with low tide. Same as a wave. More water = more mass.
imagine a 1000 tones of water is about 125m of aqueduct. 8 tonnes per M (4M wide 2M deep). If I create a wave which increases the height of water by 150mm then I have another 600kg of water at that point in the system and somewhere else will have 600kg less (the wave trough).
Its very easy to to prove, take an empty ice cream container fill it half full and hold it in your hands, now tip one side so that the water flows to the other, guess which side now feels heavier.
If the barge is moving and creating a wave temporarily pushing the water over the aqueduct, the supports will be subject to extra (tiny) load. If the barge its still along with the water it wont.
imagine a 1000 tones of water is about 125m of aqueduct. 8 tonnes per M (4M wide 2M deep). If I create a wave which increases the height of water by 150mm then I have another 600kg of water at that point in the system and somewhere else will have 600kg less (the wave trough).
Its very easy to to prove, take an empty ice cream container fill it half full and hold it in your hands, now tip one side so that the water flows to the other, guess which side now feels heavier.
If the barge is moving and creating a wave temporarily pushing the water over the aqueduct, the supports will be subject to extra (tiny) load. If the barge its still along with the water it wont.
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Tell me what you think "displacement" is.
The water and the boat stay the same weight, because earths gravity is constant Displacement is another way of expressing buoyancy, it’s like lift enabling a plane to fly. But an A380 still weighs hundreds of tons.
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No (but I know why you are proposing this, because you're not precisely defining the extents of the system).
The system as a whole now weighs 1010 tons. You don't magically cause 10 tons of water to disappear from the system by dropping a 10 ton boat into it (unless the water level is at the brim somewhere and dropping your boat in causes it to overflow)
They already feel the weight of the barge, and have done in whatever proportion of the surface area of the system the aqueduct represents ever since the barge was added to the canal.
An aqueduct is 100m long. It is the only thing in the canal system. Nothing else has been built yet. No barges are in the system. It is essentially a large bathtub on stilts and carries 1000 tons of water. A ten ton barge is added to the system. The supports must now carry 1010 tons. The supports feel the weight of the barge
The barge is taken out and the canal system has some more work done on it. 50m of ground either side of the aqueduct is trenched out, same width as the aqueduct. The system is topped up with water and now contains 2000 tons of water and as a whole is 200m long, twice what it was before. A 10 ton barge is added to the system. The system as a whole now weighs 2010 tons. The aqueduct supports experience half of the weight of the barge. The other half is borne by the ground that was trenched out either side; the weight of the barge is spread
To the question of moving the barge around and whether this causes a change in the weight the supports experience, it does rather depend how infinitesimally persnickety you want to be with regards to the answer. Let's be extreme, and turn our barge sideways then drag it by both ends, establishing a large bow wave such that there is barely any water at all behind the barge and it's all piling up in front of it, and the aqueduct sides are tall enough to contain the wave. As the barge passes over the aqueduct, pushing this massive wave of water with it, the aqueduct will experience the extra weight of the wave, as it's effectively a temporary return to something like what we had before (the system closed at both ends, causing all the water to sit on the aqueduct). This time it isn't closed at both ends so there isn't a large volume of water sitting static above the bridge, but the fact that end is moving and pushing the water with it means that for a short time, we're piling water up over the bridge.
If it's hard to conceive, let's have two barges that are a really good fit when wedged sideways in the canal, barely any water gets past them. Let's drag them towards each other so the water level builds up between them, until it can't escape past them he sides and under and establish a level. For the time that extra water over and above the resting canal level, is piled up on top of the bridge its weight has to be borne by the bridge
Your question is too loosely stated to be able to answer effectively but if you're willing to accept any change in weight, however small, then yes the stanchions of the aqueduct will experience some change in the amount of weight they have to bear if anything moves in the water such that it pushes some water from somewhere "not above the bridge" to become "above the bridge". A duck swimming onto the bridge, pushing a a small wave ahead of itself that ripples across the water on the bridge as it peters out will temporarily cause a few extra grams to be borne by the bridge
Does taking some minutes to sail a 10 ton barge over an aqueduct carrying 1000tons of water, cause the supports to have to carry an extra 10 tons for some minutes? No
Does taking some minutes to drag a vastly hydro-undynamic object through the water such that 10 tons of water ends up piled up in front of the object, proceeding along at the same speed as that object (as the object chases the wave down the canal), cause the supports to have to bear an extra 10 tons for those minutes? Yes
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On the surface the pressure is 1 bar pressing around us.
So atmospheric pressure, the downward force of gravity, and the upward thrust of buoyancy all play their part. That must mean that some of the additional weight of the boat floating must pass through to the bridge supports and then go earth.
Unless the moon is overhead, or on the other side of the planet, or moving between those positions.
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No, atmospheric pressure is the same, bouyancy of the boat is the same as the bouyancy of the water it occupies.
So no difference if you consider the mass of the whole of the connected canal system water to be infinite in comparison to that of the boat.
Even if not, the weight is supported equally on all the columns because water spreads out.
The limit on length is the distance(s) to the next locks, you could guess that the boat occupies 1/n of the volume of water within its length and get to a figure pretty quickly for a fixed length of water.
Eg barge 60m, unlocked water 60km, barge occupying 1/4 the cs area of the canal, canal water depth of 2m increases about 2000(60/60k x4)) = half a mm or so.
All that happens when the barge moves into the viaduct is that it replaces some water of the same mass, so it makes zero difference.
If you craned a barge into the canal, which had a total mass of say 2kT, then the effect would be exactly the same (once things had levelled out) as if you'd poured 20k cubic metres of water into the canal. About the same 0.5mm.
