There exist dynamic and static properties, but for this question, a 1D static gravitation force is the only concern. In this the water has no net effect, whether trapped or free to flow. The net static force is only the difference in density x volume of metal.
The acceleration could then be considered by a=F/m for the mass of metal,m, ignoring dynamic fluid friction.
Les Jones said:(It will be at the same point in water as it is in air.) If the two holes of equal volume are an equal distance from the centre of gravity along a straight line then it would not change the centre of gravity but otherwise they would.
It depends on the difference in density only and volume occupied therein. Unsealed the water has no net force., and thus only the density and volume of metal are factors. But sealed , it depends on the assumption for sealed with water or air.I agree with Les' analysis assuming the reference point is the CG in air,
John
A solid piece of metal with holes is placed in water. In this submerged condition, does the water inside the holes count toward the part center of gravity?t
Even more perplexing to me, what happens if some of the holes get completely sealed off from the aqueous environment, while others do not? Does this theoretically change its center of buoyancy or center of gravity?
There exist dynamic and static properties, but for this question, a 1D static gravitation force is the only concern. In this the water has no net effect, whether trapped or free to flow. The net static force is only the difference in density x volume of metal.
The acceleration could then be considered by a=F/m for the mass of metal,m, ignoring dynamic fluid friction.
Thus, one could replace the wood handle of the aforementioned hammer with a metal handle that has a lot of sealed holes.Iawia said:what happens if some of the holes get completely sealed off from the aqueous environment
No, so long as ALL holes contain water and the object is fully submerged. The buoyancy provided by the water will act upon the metal displacing water equally. In other words, no different that that buoyancy (however slight) provided by the air it was in, prior to being submerged.A solid piece of metal with holes is placed in water. In this submerged condition, does the water inside the holes count toward the part center of gravity?
Two answers:... what happens if some of the holes get completely sealed off from the aqueous environment, while others do not? Does this theoretically change its center of buoyancy or center of gravity?...
My emphsis.Let's say you have an cylindrical object made of a material called water. There is a large hole in the object off its center axes. The location of CG is: if the hole is on the left, CG will be located in the right plane.
OK.Now you 'fill' that hole with water. Does the material added to the hole count toward cg? I assume everyone here would say yes, and the CG would shift to back to center.
Here's where you make a conceptual leap that (you'll excuse me) " doesn't hold water". The object, all of which is water, has a CG in the middle. The so-called "entrained water" is no different that the rest of the object, and this entire object is IN water. Nothing is contained or has a different density and, therefore, there is no, nor can there be, a CG.Now place the object in water as well. According to folks statements it will have to shift back to the right plane due to the fact that the entrained water in the hole contributes nothing. Hmm.
The fallacy of your argument is that you are assuming that water in a hole of a cylinder contributes to the weight of that cylinder if submerged in water. It does not.The "entrained" water is, and can only be, part of the material (the water) in which the cylinder is submerged, i.e., it can only contribute to the buoyancy side of the equation.Now suppose we were to alter the material properties only of the object (not the contents of the hole) by changing the water density until it becomes a solid. Clearly, changing the density of an object will change the overall CG for an unsymmetric part, now where is CG and does the entrained water contribute to its location?
Again, my emphasis.I work for a company who deals with entrained water within vessels...
You have too many variables and terms, all being mushed together without regard to context, to have proven such a statement.... Hence, forces at play are not in question, only CG.
A picture is worth a thousand words and an experiment is worth a thousand thought experiments.
Pascal's law or the principle of transmission of fluid-pressure (also Pascal's Principle[1][2][3]) is a principle in fluid mechanics that states that pressure exerted anywhere in a confined incompressible fluid is transmitted equally in all directions throughout the fluid
The metal will weigh less submerged by the amount of water displaced. Removing metal above the surface will lighten the load, Submerging the altered metal will lighten the load by the same ratio as before. If the metal entraps a multitude of vacuum tubes, then it will be lighter when submerged because water will be displaced by the vacuum tubes. If many of the vacuum tubes are displaced from the surface center of gravity, the submerged CG will change. If some of the vacuum tubes lose their seal and water enters, they lose their buoyancy and the CG changes again. Any questions?Hey all,
We have been debating for a while on a specific topic and I was wondering maybe if someone here could supply the answer. You guys have pretty much been able to answer everything else I have ever desired to know.
Here is the problem statement:
A solid piece of metal with holes is placed in water. In this submerged condition, does the water inside the holes count toward the part center of gravity? Even more perplexing to me, what happens if some of the holes get completely sealed off from the aqueous environment, while others do not? Does this theoretically change its center of buoyancy or center of gravity?
The second that I think I understand it, I don't.
-t
So there seems to be an agreement that entrained water does not count toward an objects center of gravity. I am not convinced either way yet myself because if you do a thought experiment where one puts a small rock within the hole, that pebble counts towards its center of gravity. However, according to the statements here water which is also contained within the hole does not.
Now consider a second thought experiment. Consider the same object in air. Consider heavy moisture in the air. If one was to squeeze all of the moisture out of the airspace occupied by the hole and set it upon the surface of the object, that mass of moisture would count toward the CG, but as particle floating in air it does not contribute to its CG. Now consider that hole sealed off from its environment and the object is heated so that the moisture from the surface is jettisoned into the hole's same airspace, is that not also part of its mass due to its closed nature? I feel there is something fishy about just simply opening or closing an aperture to alter the center of gravity.
still puzzled. I am building an experiment for it now.
I work for a company who deals with entrained water within vessels so it does have some definite benefits to knowing the truth behind this.
Here's the deal. Follow me really quick on one extreme scenario.
Let's say you have an cylindrical object made of a material called water. There is a large hole in the object off its center axes. The location of CG is: if the hole is on the left, CG will be located in the right plane.
Now you 'fill' that hole with water. Does the material added to the hole count toward cg? I assume everyone here would say yes, and the CG would shift to back to center.
Now place the object in water as well. According to folks statements it will have to shift back to the right plane due to the fact that the entrained water in the hole contributes nothing. Hmm.
Impossible and conflicting conditions. For instance, balsa wood has an extremely low density, but is a solid. Mercury has a very high density, and is not a solid. Cranking up the density does not make a solid.Now suppose we were to alter the material properties only of the object (not the contents of the hole) by changing the water density until it becomes a solid.
How does an overall CG differ from a regular CG? Unsymmetric parts have a CG, too. Changing density of a object will not change its CG.Clearly, changing the density of an object will change the overall CG for an unsymmetric part,
That's right. They change because their displacements and force application positions change.now where is CG and does the entrained water contribute to its location? I am trying to demonstrate that physical principles and natural laws should not change merely because material properties shift.
As I said before, it all depends on force application positions.To be clear certainly the resultant 'wet weight' (weight - buoyancy) force will not change however, I am not certain the CG remains unaffected. Hence, forces at play are not in question, only CG.
This is ridiculous, strantor. No longer interested in your nonsense.A picture is worth a thousand words and an experiment is worth a thousand thought experiments.
Take an empty mason jar and fashion a long counterbalance handle/arm for it out of clothes hanger. Find the CG, hang the apparatus from a string from the CG. Dunk it in your bathtub and make sure the jar fills. Observe CG.
Now remove it, cap the jar, find the new CG, and Dunk it again.
If you can show that the two experiments yield the same result and/or if you can show that dunking the open jar apparatus changes the GC, I'll send you a whole $0.47 via paypal.
Care to elaborate? I wasn't trying to be nonsensical so I'm a little baffled by your response. What is so ridiculous about the experiment?This is ridiculous, strantor. No longer interested in your nonsense.
You're right, strantor. My sincere apologiesCare to elaborate? I wasn't trying to be nonsensical so I'm a little baffled by your response. What is so ridiculous about the experiment?
EDIT: I can't help but wonder if maybe you're mistaking me to be OP/TS? This is not my thread. The post you quoted was my first reply to this thread.
???You have too many variables and terms, all being mushed together without regard to context, to have proven such a statement.
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