Water displacement.

[Trazor]

sorry and i wasnt attempting derogatory sarcasm.

No problem, you will experience much worse on this forum...............

mass does not displace its own weigh in water, it displaces its own volume, thats when archemdes screamed

geez this water is too fooking hot

A body which floats displaces its own weight in water....Archimedes principle.
If it has displaced its own volume, then it is under water.

 

[Shytalkz]

If it has displaced its own volume, then it is under water.

If the top of it was at the surface of the water, that would be the same

 

[tim west]

If it has displaced its own volume, then it is under water.

If the top of it was at the surface of the water, that would be the same

not 100% sure of that until it broke the surface tension of the water the surface would be supporting the weight and would curve slightly without touching the very top edge, wouldnt it? or do you mean the water level exactly matches the objects height and its sitting on the bottom?

 

[Shytalkz]

No, I mean the top of the object and water are coincident. Allowing for the meniscus, of course

 

[tim west]

would it be concave or convex in a canal?

 

[Shytalkz]

Convex, if the water was right up to the top of the sides. On the sides themselves, will report back after having a bath

 

[WDIK]

A body which floats displaces its own weight in water....Archimedes principle.
If it has displaced its own volume, then it is under water.

archimedes wasnt interest in things floating, he was actually tasked to develope a means of identifying wether a substance was gold or not, and he identified that different substances displace different volumes of water compared to their own weight.

if a body displaces a weight of water that is greater than the weight of the body then it will float if not it wont

 

[Softus]

but... does the structure recognise the fact that it is more top heavy?

what i mean is, can the mass of such objects, floating upon such a structure, destabilize or cause an imbalance to say a very tall aqueduct.

Provided the barge moves through at a steady speed, and keeps a straight course, then the effect will be virtually nil.

There are two effects to consider:- pressure, mass, and the momentum of moving water.

Any increase in depth, whether caused by displacement for a buoyant object, or for a sunken object, or by rainfall, or whatever, will increase the pressure in the water, because pressure increases with depth. This translates to a force on everything, at a given depth, that the water touches, equally, and in all directions. This means that the pressure on the bottom of the 'duct is the same as that on the piece of the 'duct sides which are right at the bottom.

The force created by the mass of static water is met by the vertical component of a reactive force created by the structure of the aquaduct, and the canal bed (i.e. the Earth's crust) elsewhere. The deeper the water, the greater the force.

What you have to remember is, if the barge weighs 10,000lb, it displaces 10,000lb of water, which will even out over the whole canal system.
It is exactly the same as removing the barge and pouring 10,000lb of water into the canal.

Spot on.

A floating boat results in an increase in water level, throughout the canal, which increases the pressure and also increases the force on the bottom of the canal. So the force created by the mass of a floating boat will be borne by the substrate of the entire canal, not just the aquaduct.

If the barge were to veer from side to side, as it passed through, then it would put a impart a small force to each side, as it veered to that side.

Correct.

The effect of moving water, whether created by a boat or something else, doesn't increased the force on the canal bed that's vertically below the crest of any wave that's formed, but the energy in the moving water has to be absorbed by whatever it meets, so there is a horizontal force on the side of the canal. You can feel the effect of this force if you stand waist-deep in the sea and wait for a swell to 'hit' you.

I,m sure the designers would have allowed for this.

Demonstrably, they have.

The only force the barge can impart, is by water movement. But at the speed barges travel this will always be quite small

Again, demonstrably, it's small enough to be coped with.

 

[WDIK]

who said this erre barge had an engine?

geez that will affect is bouyancy


no one stipulated motion, or how long this very short canal is

 

[Space cat]

and how do you increase the pressure in one part of a open vessell?

As long as the water is static, the pressure depends only upon the depth. Once you add movement all bets are off. You have to apply Bernoulli's equation - modified to allow for viscosity. Hydrodynamics is a seriously complex business. I spent three years studying water waves - then I had to get a job!

Edit:

no one stipulated motion

Yes they did. It was in the original post.

 

[WDIK]

true

 

[tim west]

I spent three years studying water waves - then I had to get a job!

surfing in oz were you?

 

[mark vincent]

Does an aqueduct's stanchions/supports recognise or feel the weight of a barge floating across the water as it passes over them?

Or, is this a simple displacement issue?

If you have 1,000,000 tons of water and add a boat to it which weighs 10 tons, you are going to have a total weight of 1 million and ten tons resting on the river bed, so therefore there would be more weight on the bridge. Although the weight would be evenly distributed the length and breadth of the canal and viaduct. the viaduct would feel the weight of the barge as soon as it enters the water

 

[JohnD]

except that the canal has a maintained water level, and will spill out any appreciable increase, so within practical limits, there will be no increase.

 

[Shytalkz]

If all the boats, ships, barges and so forth were taken out of the sea, harbours, rivers, docks etc simultaneously, how far would water levels drop?