Post by rmc on Jan 21, 2015 3:49:08 GMT
{Moved to Submissions as an example as to how to write an idea up for this section of the board - CM}
Surprisingly, there are differing answers, depending upon where you look:
Answer 1: Yes. Like a sea saw, or beam balance, it will wobble about until ultimately coming to rest, level with the surface of the Earth, (horizontally).
Answer 2: No. Since it is balanced, and on a frictionless pivot located at the center of mass, it will rest in any position we leave it, level or not.
Answer 3: Neither. It will ultimately end up hanging vertically.
Answer 1:
In the following video, this first technician, declares that the propeller should come to rest level with the surface of Earth (seen at about 1:17 into the video):
Answer 2:
In this next video, another technician declares that a balanced item (like the propeller) will rest in any position. (seen at about 2:00 into the video):
Answer 3:
And, if we look at a magnet pulling on a propeller made of steel, we could come to the conclusion that, like a magnet, an object nearest to the predominant source of gravity is pulled harder than an object further away. So, like the steel propeller, when one blade gets too close to the magnet, the nearer blade ultimately points in the magnet's direction: Thus, we might conclude that a propeller would likely end up with one of its two blades pointing directly TOWARD Earth (not level after wobbling about). In fact, staying horizontal takes a serious amount of balancing effort and is easily knocked out of line.
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So, which answer is correct?
First, where is the center of mass? Where is the center of rotation? If we watch the process for balancing a propeller, we see that the effort is in putting the center of mass directly inline with the center of rotation. This is achieved by removing or adding material until the blade can be put in any position without it turning afterward, (on its own). Would this behave the same if the bearing were frictionless though?
Looking at a sea saw or beam balance, is a sea saw, or beam balance, really pivoting exactly at the center of mass? Let's take a closer look: In a sea saw, the bracket serving as a balancing-pivot is bolted to one side of the board, usually the lower side of the board. There is some imbalance top-to-bottom as a result, though small. So, with this slight offset, we get a pulling force. For instance, a beam balance hangs masses beneath a leveling-arm. So, the center of rotation is offset; with the true center of mass beneath it. For the sea saw, however, the center of mass is offset directly above the center of rotation, ever so slightly. In either case, the effect Is the same: The offset mass turns the apparatus until the device is level; ending with the center of mass either directly toward, or directly away from the surface of Earth.
If a balanced propeller uses an ordinary ball bearing, instead of the proposed frictionless bearing, and the propeller stays in any position we put it, is this the result of some sort of resistance holding the prop stationary? Does this mean that the result we witnessed earlier regarding the magnet and steel propeller was too extreme of an example to be apt? Typically speaking, does gravity behave sufficiently like a magnetic that it always causes an item nearer to be pulled harder than one further away? Are the propeller blades far enough apart from each other to achieve an appreciably-greater pull of gravity between them?
To answer these questions involves something referred to as Tidal Force. Tidal Force is an appreciably greater pull of gravity seen over the length of an object. An extreme example might be the spaghettification of an object falling into a black hole. For the black hole example, the pulling force on one end of the object becomes very obviously greater than the other end (at a certain point falling in). The result? The object gets pulled in the same direction, but one end goes much faster than the other, and the object is completely pulled apart!
To determine if we have any Tidal Forces at work within our propeller, we'll need to set up a truly frictionless pivot and then suspend our propeller near a good primary source of gravity.
The Cavendish Experiment of 1798 forms the bases of our experiment.
To familiarize yourself with the Cavendish apparatus, view the following (or other Internet search):
Cavendish Experiment for value of G:
An Altered Cavendish Experiment:
Here's what I propose: We'll need a concave rare earth magnet, a thin sheet of Pyrolytic Graphite that has been carefully cut by computer control into the silhouette of a propeller, constructed such that its shape is symmetric each way. We'll need a glass-covered vacuum chamber, and, we'll need a large, massive lead ball to act as the predominant source of gravitation (touching the perimeter edge of the concave magnet apparatus). An extra sheet of Pyrolytic Graphite and an arrangement of flat magnets will help create a control experiment. A small static discharge probe is required to remove any static charges.
To see an example of the Pyrolytic Graphite material floating over magnets, see this site:
Pyrolytic Graphite
The thin sheet of Pyrolytic Graphite is curved to match the shape of the concave surface of the magnet and is set inside the concave rare earth magnet where it floats. It floats because the Pyrolytic Graphite repels the magnetic field, but since the propeller-shaped sheet of Pyrolytic Graphite is slightly curved and is resting, flat-ways, at the bottom of a concave dish, it also settles into a position as though it has an axis of rotation at its middle. This will serve as our "Cavendish" torsion balance.
A large lead ball is secured very near to the edge of concave magnet dish. We want the edge of the concave magnetic dish to touch the perimeter of the massive lead ball, while the dish is basically level with the floor. We want this arrangement to stay in this configuration. Setting the curved, propeller-shaped sheet of Pyrolytic Graphite into the magnetic dish and arranging it so it is oreiented 45 degrees from a tangent line, (formed perpendicular with the touching point between the lead ball and magnetic apparatus), puts our propeller into its initial resting position.
Once static charges are removed by briefly grounding the propeller to the lead ball with a small static discharge probe, the entire set of items can be covered by the glass bell-shaped lid of the vacuum chamber and air removed. Now, we have a rig that lets us observe the nature of a propeller when balanced on a frictionless pivot, near a predominant source of gravity.
If the length of the propeller is short enough, and the predominant gravity from the lead ball equal over the short length of the propeller, the propeller should remain at 45 degrees. However, if the gravity is appreciably more for the blade closer to the lead ball, (wherein Tidal Forces ARE apparent) the propeller should ultimately rest perpendicular (not horizontal) to the lead ball (coming to rest after sweeping back and forth for a time).
But, if the propeller-analog manages to stay at 45 degrees, even while being this far off from accurate scale, (very large with respect to the Earth-analog it is paired up with), then, when the real propeller manages to stay at 45 degrees at normal scale, it could NOT possibly be experiencing any appreciable Tidal Force from its Earth counterpart. (Because the real propeller is so much shorter than the analog propeller when compared to each Earth or Earth standin).
And, lastly, to prove that our set up was under the influence of gravity produced by the lead ball, we'll reset the experiment. This time, instead of a concave magnetic dish, we'll use the set of flat magnets, mounted to the perimeter of the lead ball, such that the flat surface is level with Earth's surface and float the Pyrolytic Graphite sheet this way. If the lead ball is producing enough gravity to accomplish the goal of our experiment, the sheet of Pyrolytic Graphite will simply be attracted over to the lead ball as it floats.
To see an example of a concave shaped magnet, see this site:
Concave magnet
(A suitable lead ball may need to be formed, custom-made).
Acknowledgements to the following members for contributing greatly to this thread: Watcher56, the light works, OziRiS and silverdragon.
The original thread and their contributions can be found here:
link
"Does a balanced propeller, hung motionless on a frictionless bearing, end up resting horizontally?"
Surprisingly, there are differing answers, depending upon where you look:
Answer 1: Yes. Like a sea saw, or beam balance, it will wobble about until ultimately coming to rest, level with the surface of the Earth, (horizontally).
Answer 2: No. Since it is balanced, and on a frictionless pivot located at the center of mass, it will rest in any position we leave it, level or not.
Answer 3: Neither. It will ultimately end up hanging vertically.
Answer 1:
In the following video, this first technician, declares that the propeller should come to rest level with the surface of Earth (seen at about 1:17 into the video):
Answer 2:
In this next video, another technician declares that a balanced item (like the propeller) will rest in any position. (seen at about 2:00 into the video):
Answer 3:
And, if we look at a magnet pulling on a propeller made of steel, we could come to the conclusion that, like a magnet, an object nearest to the predominant source of gravity is pulled harder than an object further away. So, like the steel propeller, when one blade gets too close to the magnet, the nearer blade ultimately points in the magnet's direction: Thus, we might conclude that a propeller would likely end up with one of its two blades pointing directly TOWARD Earth (not level after wobbling about). In fact, staying horizontal takes a serious amount of balancing effort and is easily knocked out of line.
-----------------------------------------------------------------------
So, which answer is correct?
First, where is the center of mass? Where is the center of rotation? If we watch the process for balancing a propeller, we see that the effort is in putting the center of mass directly inline with the center of rotation. This is achieved by removing or adding material until the blade can be put in any position without it turning afterward, (on its own). Would this behave the same if the bearing were frictionless though?
Looking at a sea saw or beam balance, is a sea saw, or beam balance, really pivoting exactly at the center of mass? Let's take a closer look: In a sea saw, the bracket serving as a balancing-pivot is bolted to one side of the board, usually the lower side of the board. There is some imbalance top-to-bottom as a result, though small. So, with this slight offset, we get a pulling force. For instance, a beam balance hangs masses beneath a leveling-arm. So, the center of rotation is offset; with the true center of mass beneath it. For the sea saw, however, the center of mass is offset directly above the center of rotation, ever so slightly. In either case, the effect Is the same: The offset mass turns the apparatus until the device is level; ending with the center of mass either directly toward, or directly away from the surface of Earth.
If a balanced propeller uses an ordinary ball bearing, instead of the proposed frictionless bearing, and the propeller stays in any position we put it, is this the result of some sort of resistance holding the prop stationary? Does this mean that the result we witnessed earlier regarding the magnet and steel propeller was too extreme of an example to be apt? Typically speaking, does gravity behave sufficiently like a magnetic that it always causes an item nearer to be pulled harder than one further away? Are the propeller blades far enough apart from each other to achieve an appreciably-greater pull of gravity between them?
To answer these questions involves something referred to as Tidal Force. Tidal Force is an appreciably greater pull of gravity seen over the length of an object. An extreme example might be the spaghettification of an object falling into a black hole. For the black hole example, the pulling force on one end of the object becomes very obviously greater than the other end (at a certain point falling in). The result? The object gets pulled in the same direction, but one end goes much faster than the other, and the object is completely pulled apart!
To determine if we have any Tidal Forces at work within our propeller, we'll need to set up a truly frictionless pivot and then suspend our propeller near a good primary source of gravity.
The Cavendish Experiment of 1798 forms the bases of our experiment.
To familiarize yourself with the Cavendish apparatus, view the following (or other Internet search):
Cavendish Experiment for value of G:
An Altered Cavendish Experiment:
Here's what I propose: We'll need a concave rare earth magnet, a thin sheet of Pyrolytic Graphite that has been carefully cut by computer control into the silhouette of a propeller, constructed such that its shape is symmetric each way. We'll need a glass-covered vacuum chamber, and, we'll need a large, massive lead ball to act as the predominant source of gravitation (touching the perimeter edge of the concave magnet apparatus). An extra sheet of Pyrolytic Graphite and an arrangement of flat magnets will help create a control experiment. A small static discharge probe is required to remove any static charges.
To see an example of the Pyrolytic Graphite material floating over magnets, see this site:
Pyrolytic Graphite
The thin sheet of Pyrolytic Graphite is curved to match the shape of the concave surface of the magnet and is set inside the concave rare earth magnet where it floats. It floats because the Pyrolytic Graphite repels the magnetic field, but since the propeller-shaped sheet of Pyrolytic Graphite is slightly curved and is resting, flat-ways, at the bottom of a concave dish, it also settles into a position as though it has an axis of rotation at its middle. This will serve as our "Cavendish" torsion balance.
A large lead ball is secured very near to the edge of concave magnet dish. We want the edge of the concave magnetic dish to touch the perimeter of the massive lead ball, while the dish is basically level with the floor. We want this arrangement to stay in this configuration. Setting the curved, propeller-shaped sheet of Pyrolytic Graphite into the magnetic dish and arranging it so it is oreiented 45 degrees from a tangent line, (formed perpendicular with the touching point between the lead ball and magnetic apparatus), puts our propeller into its initial resting position.
Once static charges are removed by briefly grounding the propeller to the lead ball with a small static discharge probe, the entire set of items can be covered by the glass bell-shaped lid of the vacuum chamber and air removed. Now, we have a rig that lets us observe the nature of a propeller when balanced on a frictionless pivot, near a predominant source of gravity.
If the length of the propeller is short enough, and the predominant gravity from the lead ball equal over the short length of the propeller, the propeller should remain at 45 degrees. However, if the gravity is appreciably more for the blade closer to the lead ball, (wherein Tidal Forces ARE apparent) the propeller should ultimately rest perpendicular (not horizontal) to the lead ball (coming to rest after sweeping back and forth for a time).
But, if the propeller-analog manages to stay at 45 degrees, even while being this far off from accurate scale, (very large with respect to the Earth-analog it is paired up with), then, when the real propeller manages to stay at 45 degrees at normal scale, it could NOT possibly be experiencing any appreciable Tidal Force from its Earth counterpart. (Because the real propeller is so much shorter than the analog propeller when compared to each Earth or Earth standin).
And, lastly, to prove that our set up was under the influence of gravity produced by the lead ball, we'll reset the experiment. This time, instead of a concave magnetic dish, we'll use the set of flat magnets, mounted to the perimeter of the lead ball, such that the flat surface is level with Earth's surface and float the Pyrolytic Graphite sheet this way. If the lead ball is producing enough gravity to accomplish the goal of our experiment, the sheet of Pyrolytic Graphite will simply be attracted over to the lead ball as it floats.
To see an example of a concave shaped magnet, see this site:
Concave magnet
(A suitable lead ball may need to be formed, custom-made).
Acknowledgements to the following members for contributing greatly to this thread: Watcher56, the light works, OziRiS and silverdragon.
The original thread and their contributions can be found here:
link
