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Why this discrimination Options
dev_sircar
Posted: Tuesday, May 11, 2010 2:18:04 PM

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Why this discrimination?

If u place a block of wood between a magnet and a piece of iron, can the magnet attract the iron?
If u place a block of wood between a falling apple and mother Earth will the apple still fall??
Winnie
Posted: Tuesday, May 11, 2010 2:26:08 PM
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dev_sircar wrote:


If u place a block of wood between a magnet and a piece of iron, can the magnet attract the iron?


Yes.

Quote:
If u place a block of wood between a falling apple and mother Earth will the apple still fall??


Yes.
mailady
Posted: Tuesday, May 11, 2010 2:32:37 PM
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Earth=bigger magnet
Geeman
Posted: Tuesday, May 11, 2010 2:38:39 PM

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dev_sircar wrote:
Why this discrimination?

If u place a block of wood between a magnet and a piece of iron, can the magnet attract the iron?
If u place a block of wood between a falling apple and mother Earth will the apple still fall??

I'm not quite sure what you're asking, but from the content of these sentences, I think the difference is electromagnetism versus gravity.
uuaschbaer
Posted: Tuesday, May 11, 2010 2:51:22 PM

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Attraction ≠ falling. For falling there need to be space between the apple and the woodblock, if there is no space between them you will be left with an apple attracted by the earth's mass but not falling. That aside, what is it, specifically, that you would expect to be the difference between the two cases?
Cat
Posted: Tuesday, May 11, 2010 6:08:04 PM

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I believe the apple will fall to the wood block, the attraction as Geeman says is gravity toward the earth's center. A magnet will attract a piece of iron with a wood block in between but the magnet needs to be large enough in order for the iron to move toward the magnet. It would attract the iron and trap the wood in between. The magnetic force cannot be seen but it is there even if it is not strong enough to move the iron. Was this a science question or a philosophical rhetorical question and I'm too logical to pick up on it? d'oh!
kaleem
Posted: Tuesday, May 11, 2010 9:18:08 PM
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dev_sircar wrote:
Why this discrimination?

If u place a block of wood between a magnet and a piece of iron, can the magnet attract the iron?
If u place a block of wood between a falling apple and mother Earth will the apple still fall??



Yes
Yes



srirr
Posted: Wednesday, May 12, 2010 12:05:34 AM

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dev_sircar, can you please elaborate what you intend to ask?

Of course, the question is not what it seems to be. Thinking on the title "Why this discrimination", I can figure out dev_sircar has the hidden meaning in the questions. I feel it is about two persons (or things) that are mutually attracted to each other. Even if there is some hinderance, the attraction prevails. And the attraction is not for the blocking material, it is for your beloved.

Khan
Posted: Wednesday, May 12, 2010 2:32:49 AM
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Very simple reason.If this block of wood is very very thin and the magnet is very big with a lot of magnetic field the magnet will attract the iron.Since the earth is a very very big powerful magnet that is why it attracts the objects towards itself despite the fact you put any other object between the earth and the falling object.Another reason is that the object you put between the earth and the falling object is itself attracted towards the earth.
Luftmarque
Posted: Wednesday, May 12, 2010 2:51:52 AM

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Khan wrote:
Very simple reason.If this block of wood is very very thin and the magnet is very big with a lot of magnetic field the magnet will attract the iron.Since the earth is a very very big powerful magnet that is why it attracts the objects towards itself despite the fact you put any other object between the earth and the falling object.Another reason is that the object you put between the earth and the falling object is itself attracted towards the earth.

This is incorrect. The earth is a very large magnet (thus the North & South magnetic poles) BUT that is NOT why it engages in mutual attraction with objects with mass. That's gravity. As posted previously, we're talking about two different forces: electromagnetism and the very much stranger gravity. Or maybe the topic isn't about scientific forces at all, I'm not sure.
mihermano
Posted: Wednesday, May 12, 2010 3:10:47 AM
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1. It depends.
2. It depends.

Need many more details for a more detailed answer.
kisholoy mukherjee
Posted: Wednesday, May 12, 2010 5:13:41 AM
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Luftmarque wrote:
Khan wrote:
Very simple reason.If this block of wood is very very thin and the magnet is very big with a lot of magnetic field the magnet will attract the iron.Since the earth is a very very big powerful magnet that is why it attracts the objects towards itself despite the fact you put any other object between the earth and the falling object.Another reason is that the object you put between the earth and the falling object is itself attracted towards the earth.

This is incorrect. The earth is a very large magnet (thus the North & South magnetic poles) BUT that is NOT why it engages in mutual attraction with objects with mass. That's gravity. As posted previously, we're talking about two different forces: electromagnetism and the very much stranger gravity. Or maybe the topic isn't about scientific forces at all, I'm not sure.


In the first case:
If u place a block of wood between a magnet and a piece of iron, can the magnet attract the iron?
Yes, the magnet will attract the iron piece. But there can obviously be attraction without movement. The force of attraction must be greater than the summation of all inertial forces, the frictional forces and the other forces acting on the body in the opposite direction for either the body or the magnet to move (any one can move according to the direction of field and constraints of inertia (mass)). Most likely, the magnet is horizontally placed to the earth ( or more precisely, we are considering motion of the iron piece only in the horizontal direction). So, gravity will not play a part in this case. (since work done by a force in a direction perpendicular to it is zero, as work = scalar or dot product of force and displacement, which comes out to force*displacement*cos (angle) and cos 90 = 0) If is however not exactly horizontal, then the resultant field or force will be due to both gravity as well as magnetic force. Hence, in case there is a movement of the magnet, the kinematics of its motion will be different than when there was no effect of gravity.
In the second case:
If u place a block of wood between a falling apple and mother Earth will the apple still fall??
Here, there will certainly be movement, because the earth is too big to move. SO, both the apple and the block will fall to the earth.
When a body falls towards the earth, I think there is the force of magnetism acting as well, but it is undoubtedly the gravitational pull towards its center that is almost entirely responsible for the falling of the body.

P.S: I'm not entirely sure but I think the wood in the first question might actually increase the net effect of the magnetic field on the body. That is because the permeability of the medium in between the magnet and the body will increase (this is where am not sure) when there is a wood piece in between. Permeability of air is almost 1, and if in case of wood it is greater, then the field effect should increase, not decrease.
Luftmarque
Posted: Wednesday, May 12, 2010 5:33:23 AM

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<self-edited post revision #1>
I like that KM point that wants to differentiate between attraction (a sort of potential) and movement (kinetic), it's a good distinction to make. One fine point: any two bodies with mass will attract each other and, theoretically at least, there is some non-zero infinitesimal movement of the earth towards the falling apple. I always enjoyed the fact that, say, the sun and the earth revolve around their mutual center of gravity, which I believe is somewhere within the sun, but not at the exact center of the sun.

Another interesting complication is to consider the atomic forces that keep the apple or magnet from falling or being attracted right through the wood block. Those are fun forces.
kisholoy mukherjee
Posted: Wednesday, May 12, 2010 5:37:38 AM
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Luftmarque wrote:
One fine point: any two bodies with mass will attract each other and, theoretically at least, there is some non-zero infinitesimal movement of the earth towards the falling apple. [/color]


Yes, that is true. It is just that we are unable to see it. Since the acceleration of the earth is given by (mass of body* 9.8/mass of the earth), where the denominator is >> the numerator) Just like when you try your best to move a wall, but you can't. But there are definitely some internal effects inside the wall (remember Hooke's law, stress prop. to strain) whenever you push it.
michiko
Posted: Wednesday, May 12, 2010 7:23:57 AM
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the question is unclear. i actually think that he just used the comparison between earth's gravity and a simple magnet to hide the meaning of the subject matter of his inquiry.
Raparee
Posted: Wednesday, May 12, 2010 8:30:34 AM

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I'm just confused as to how either question deals with discrimination at all. Regardless of the particular forces involved, the questions show no discrimination in my mind - they are simply facts of how these forces (be it gravity, electromagnetism, kinetic energy, etc) react to each other and a particular circumstance. Gravity doesn't see kinetic energy going to do something and go, OH HELL NO, and butt in and not allow kinetics to do whatever it was doing.

Thus, confuzzled.
dev_sircar
Posted: Wednesday, May 12, 2010 1:28:16 PM

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My query was purely scientific in nature.It had no subtle allusion to any altogether different subject .

The confusion in my mind was whether the magnetic lines of force can permeate a block of wood while Gravity can.
kauserali
Posted: Wednesday, May 12, 2010 1:44:15 PM
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Gravity does penetrate surfaces. If it didn't, then anything that's kept above an obstruction, would experience anti-gravity. The forces of gravity do not work after a certain distance (because gravitational force= GMm/r^2, where r is the distance between the object and earth.

Magnetic lines of force work on a similar principle. After a certain distance, no attraction is possible. Because of the distance, the denominator becomes larger than numerator, the attraction is negligible . Magnetic force does penetrate thru surfaces like wood, but it has to be strong enough.
kisholoy mukherjee
Posted: Wednesday, May 12, 2010 1:46:09 PM
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dev_sircar wrote:
My query was purely scientific in nature.It had no subtle allusion to any altogether different subject .

The confusion in my mind was whether the magnetic lines of force can permeate a block of wood while Gravity can.


Thanks for the explanation dev. I actually had the same doubt, if you see my earlier post. I have found a link that says that wood has very low permeability, but so does air. It doesn't mention which one of these two has lower permeability.
http://info.ee.surrey.ac.uk/Workshop/advice/coils/mu/
I wonder how gravity really works. I mean, it is known that electromagnetic forces act by polarising the medium in between. But what about gravity?
I also don't know how electromagnetic forces act in vacuum (i mean there is no material to polarize in the medium, right?)
kauserali
Posted: Wednesday, May 12, 2010 1:55:14 PM
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KM, magnets do work in vacuum. The reason is that magnetism is an internal property. Remember permeability in free space?
kisholoy mukherjee
Posted: Wednesday, May 12, 2010 2:08:46 PM
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kauserali wrote:
KM, magnets do work in vacuum. The reason is that magnetism is an internal property. Remember permeability in free space?


I know they work in space. And yes, I know about permeability in free space, μ0. But I was asking what is the funda behind the working of magnetism in vacuum (since as far as i know the magnetic field works by the method of magnetizing, i.e. creating polarized domains in the intervening medium. But, in vacuum or free space, there isn't supposed to be anything to induce magnetism in, then what is the mechanism behind it, that was my question)
Luftmarque
Posted: Wednesday, May 12, 2010 3:16:21 PM

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Current description (post-Einstein) of gravity is that it is the distortion or curvature of 3-space that mass creates. So it's not a question of force acting through a medium or otherwise, it's a state of affairs in space itself.
Cat
Posted: Wednesday, May 12, 2010 3:46:33 PM

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Even though a surface seems solid, like a block of wood, it is mostly empty space. The "solidness" is actually the attraction of the atoms/molecules to each other. The harder the surface, for instance, the stronger the attraction between the atoms/molecules.

This is one reason I really enjoyed science, it has philosophy built into it. Makes it very interesting.
kisholoy mukherjee
Posted: Wednesday, May 12, 2010 3:47:07 PM
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Luftmarque wrote:
Current description (post-Einstein) of gravity is that it is the distortion or curvature of 3-space that mass creates. So it's not a question of force acting through a medium or otherwise, it's a state of affairs in space itself.


Yes, I had read about the space time curvature thing in Hawking's Brief history of time, but I was wondering if there was any explanation using the prevalent theories or concepts.
kisholoy mukherjee
Posted: Wednesday, May 12, 2010 3:48:27 PM
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Cat wrote:
Even though a surface seems solid, like a block of wood, it is mostly empty space. The "solidness" is actually the attraction of the atoms/molecules to each other. The harder the surface, for instance, the stronger the attraction between the atoms/molecules.



Yes, that is because the atom itself is mostly empty, and there are also many interatomic/intermolecular spaces.
Luftmarque
Posted: Wednesday, May 12, 2010 4:05:48 PM

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kisholoy mukherjee wrote:
Luftmarque wrote:
Current description (post-Einstein) of gravity is that it is the distortion or curvature of 3-space that mass creates. So it's not a question of force acting through a medium or otherwise, it's a state of affairs in space itself.


Yes, I had read about the space time curvature thing in Hawking's Brief history of time, but I was wondering if there was any explanation using the prevalent theories or concepts.

But, as far as I can tell, that is the explanation, so I must be missing some aspect of your question.
kisholoy mukherjee
Posted: Wednesday, May 12, 2010 4:36:34 PM
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Luftmarque wrote:

But, as far as I can tell, that is the explanation, so I must be missing some aspect of your question.


Here is a quote from wiki about the geometrical conceptualization of relativistic gravity:

"Many predictions of general relativity differ significantly from those of classical physics (like classical electrodynamics), especially concerning the passage of time, the geometry of space, the motion of bodies in free fall, and the propagation of light. Examples of such differences include gravitational time dilation, the gravitational redshift of light, and the gravitational time delay. General relativity's predictions have been confirmed in all observations and experiments to date. Although general relativity is not the only relativistic theory of gravity, it is the simplest theory that is consistent with experimental data. However, unanswered questions remain, the most fundamental being how general relativity can be reconciled with the laws of quantum physics to produce a complete and self-consistent theory of quantum gravity."

The other similar laws on gravity that have been formulated post Einstein have also not yet been reconciled with classical laws. That was my point about 'explaining it by prevalent concepts'.
uncoverer
Posted: Wednesday, May 12, 2010 5:00:02 PM
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kisholoy mukherjee wrote:
'explaining it by prevalent concepts'.





It was because it could not be explained by prevailing concepts that other theories like quantum or relativistic theories were developed.
Any attempt to reconcile non classical and classical theory is futile as they are two completely different scientific models .
kisholoy mukherjee
Posted: Wednesday, May 12, 2010 5:08:23 PM
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uncoverer wrote:
kisholoy mukherjee wrote:
'explaining it by prevalent concepts'.





It was because it could not be explained by prevailing concepts that other theories like quantum or relativistic theories were developed.
Any attempt to reconcile non classical and classical theory is futile as they are two completely different scientific models .


Yes, I know they are different models. But renowned scientists are working on trying to reconcile them by developing 'an unified theory'. The M theory (closely linked to the string theory is one such). I wouldn't dare to make such a statement that these attempts are futile.
uncoverer
Posted: Wednesday, May 12, 2010 5:15:07 PM
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kisholoy mukherjee wrote:


Here is a quote from wiki about the geometrical conceptualization of relativistic gravity:

"[u]Many predictions of general relativity differ significantly from those of classical physics [size=4][color=blue]


The above post was made in reply to your own comments.
I am very well aware of the Grand Unification theory or GUT as it is more widely known in scientific circles.And my comment was not in response to those but to your statement as i quote above.

uncoverer
Posted: Wednesday, May 12, 2010 5:18:14 PM
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kisholoy mukherjee wrote:


I know they work in space. And yes, I know about permeability in free space, μ0. But I was asking what is the funda behind the working of magnetism in vacuum (since as far as i know the magnetic field works by the method of magnetizing, i.e. creating polarized domains in the intervening medium. But, in vacuum or free space, there isn't supposed to be anything to induce magnetism in, then what is the mechanism behind it, that was my question)




Well the highlighted part is a novel proposal as i have not heard that explanation.
I always thought polarized domains to be the effect and not the cause of magnetism
kisholoy mukherjee
Posted: Wednesday, May 12, 2010 5:23:31 PM
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uncoverer wrote:
kisholoy mukherjee wrote:


Here is a quote from wiki about the geometrical conceptualization of relativistic gravity:

"[u]Many predictions of general relativity differ significantly from those of classical physics [size=4][color=blue]


The above post was made in reply to your own comments.
I am very well aware of the Grand Unification theory or GUT as it is more widely known in scientific circles.


That was exactly my point. Despite the inconsistencies between the two theories efforts are still on to try and reconcile them, or at least develop a common theory that can explain the action of all forces.
kisholoy mukherjee
Posted: Wednesday, May 12, 2010 5:33:39 PM
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uncoverer wrote:


Well the highlighted part is a novel proposal as i have not heard that explanation.
I always thought polarized domains to be the effect and not the cause of magnetism


I didn't mean to say that magnetism is created by polarization. I said what you said only.
However, I did ask a question as to how exactly the magnetic field or force 'travels through' or affects the medium, if at all.
dev_sircar
Posted: Thursday, May 13, 2010 1:39:32 PM

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I know about GUT.But i think while Light, sound,heat, Electro-magnetism, nuclear strong / weak forces seem amenable to being explained as different manifestation of a common force, Gravitation still stands out differently.

I have read books of some eminent scientists, who question Einstein's explanation that "Gravitation cannot act immediately at a distance".Hypothetically speaking, suppose the Sun suddenly vanishes.According to "action at a distance",our mother Earth will know at once that the Sun is no more and will chart its course accordingly.But, according to Einstein, our mother Earth will know about if after a time lag - since the information of the Sun vanishing, cannot travel at a speed greater than that of light - during which time mother Earth will be moving in its usual path.

However,as the said scientist lamented, scientific community is so firmly behind Einstein, that they do not entertain any questioning of Einstein's principles.

Some of the members suspected that my original question had some hidden meaning.In truth, I was trying to ascertain if any one thinks that, may be, Gravitation still stands out differently from magnetism.
kisholoy mukherjee
Posted: Thursday, May 13, 2010 1:47:58 PM
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dev_sircar wrote:
I know about GUT.But i think while Light, sound,heat, Electro-magnetism, nuclear strong / weak forces seem amenable to being explained as different manifestation of a common force, Gravitation still stands out differently.

Some of the members suspected that my original question had some hidden meaning.In truth, I was trying to ascertain if any one thinks that, may be, Gravitation still stands out differently from magnetism.


edit:: Yet, the governing equation of gravittaional force as proposed by Newton is similar to electromagnetism ? (or has that been done away with completely?)
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