# Is this analogy between Magnetic Force and Gravitational Force accurate in helping to understand what contributes more to a stronger magnetic force?

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• Physicist-Writer
Physicist-Writer
So, the formula for Gravitational force is F= Gm1m2/r^2

So a given mass such as the earth and a mass such as much self both contribute to an equal and opposite gravitational force on each other. But we can also think of it separately in terms of just the gravitional field generated. The Earth is huge so generates a much more powerful field Gm1/r^2 than I can, which can than induce a meaningful acceleration on me down to the earth's core. But the former interpretation seems to imply that having greater masses in both cases would generate a stronger overall gravitational force.

So for magnetism, when you have a ferromagnetic object like iron in the presence of a constant externally applied field ( say applied by some other permanent magnet or by an electromagnet), both magnets involved contribute to a magnetic force that attract each other.

But then for a paragmagnetic or diamagnetic substance (which repels), their magnetization susceptibility is millions of times weaker than that of Iron, so it's supposed to take an impressive magnetic force to generate enough force to overcome the body weight of something like a frog, which is mostly made of water which is diamagnetic, with just the force of magnetism alone.

But yet, iron which is much more magnetic than water, should be able to generate a very powerful force itself, since it's millions of times more magnetic in the first place, yet the force generated is much smaller. So what am I missing here that makes the magnetic force between iron and the permanent magnet much weaker than the force generated between a very powerful magnet and a diamagnetic material?

Physicist-Writer said:
But yet, iron which is much more magnetic than water, should be able to generate a very powerful force itself, since it's millions of times more magnetic in the first place, yet the force generated is much smaller.
Why do you say that? When you say "much smaller", you are comparing what with what else?

kuruman said:
Why do you say that? When you say "much smaller", you are comparing what with what else?
As in, in each case, you have an externallly applied magnetic field supplied by a permanent magnet, the permanent magnet in the case of the frog needs to be tremendous to induce a strong enough diamagnetic force to opposed the force of gravity to accelerate the frog upward. On the other hand, the force required to accelerate a piece of iron of the same weight as the frog would be less since iron easier to influence than the water in the frog. But yet, just like the analogy in the gravitational theory, once you magnetize iron it will also become a magnet itself so in that case wouldn't the magnetic force between the iron and its permanent magnet increase and potentially be stronger than what was generated by the water?

Physicist-Writer said:
So a given mass such as the earth and a mass such as much self both contribute to an equal and opposite gravitational force on each other. But we can also think of it separately in terms of just the gravitional field generated. The Earth is huge so generates a much more powerful field Gm1/r^2 than I can, which can than induce a meaningful acceleration on me down to the earth's core. But the former interpretation seems to imply that having greater masses in both cases would generate a stronger overall gravitational force.
Certainly. Increase either m1 or m2 and BOTH objects experience an increase in the gravitational force between them.

Physicist-Writer said:
But yet, just like the analogy in the gravitational theory, once you magnetize iron it will also become a magnet itself so in that case wouldn't the magnetic force between the iron and its permanent magnet increase and potentially be stronger than what was generated by the water?
Remember that for ferromagnetic materials the very act of applying a magnetic field will magnetize them. This magnetization is why iron is attracted to magnets, even when not initially magnetized.

There may be a difference in the force on a piece of iron vs an iron magnet at larger distances, as a weak magnetic field won't magnetize the iron very much, possibly leading to a smaller force, but I can't say for certain. Once the field strength reaches the point that the iron is magnetically saturated then there is no difference between a piece of iron that was initially magnetized vs initially unmagnetized. The force will be the same.

Physicist-Writer
Drakkith said:
here may be a difference in the force on a piece of iron vs an iron magnet at larger distances, as a weak magnetic field won't magnetize the iron very much, possibly leading to a smaller force, but I can't say for certain. Once the field strength reaches the point that the iron is magnetically saturated then there is no difference between a piece of iron that was initially magnetized vs initially unmagnetized. The force will be the same.
Ah, so yeah I was confused on why magnetic saturation, as you call it, still doesn't increase the force the same way increasing either mass ( the Earth or my mass) strengthens the force we have on each other. as in if you calculated the magnetic force between the water on the magnet, and the force between iron and the weaker magnet used to magnetize the iron, the iron becoming more magnetic won't increase the force.

Sorry, I'm still not sure if your question was answered or not. Is there something you still wanted to know or that we didn't answer?

Physicist-Writer
Drakkith said:
Sorry, I'm still not sure if your question was answered or not. Is there something you still wanted to know or that we didn't answer?
Yeah you guys helped a lot, but I think I'm still one step away from fully understanding.

I guess another way to rephrase it is, if we have the earth and myself, we together create a gravitational force as previously noted. But what if , as an analogy, I never had mass to begin with. What if it worked such that the earth "gravitonized" me first and and gave me more mass, leading to an overall increased mass of the system and thus increased magnitude of gravitational force, just like how a permanent magnet magnetizes a piece of iron now making this iron now magnetic.

The iron didn't start out magnetic, but now it is, and now it should contribute to an increased magnetic force between itself and magnet, or so I thought, until you said the magnitude of the magnetic force between the permanent magnet and the iron doesn't change even after the iron has been magnetized If I'm not mistaken.

Physicist-Writer said:
The iron didn't start out magnetic, but now it is, and now it should contribute to an increased magnetic force between itself and magnet, or so I thought, until you said the magnitude of the magnetic force between the permanent magnet and the iron doesn't change even after the iron has been magnetized If I'm not mistaken.
If the iron never magnetized, there wouldn't be a magnetic force at all between it and the magnet. It's only because the iron gets magnetized that it is attracted towards the magnet. Once the iron is magnetized by the magnet, it itself is now a magnet. Thus there should be no difference between a piece of iron magnetized temporarily and a piece of iron magnetized permanently in terms of the force of attraction, at least as long as the amount of magnetization is the same in both pieces. I say 'no difference', but real iron will probably be slightly different since magnetically 'soft' and 'hard' pieces of iron have differences that make them magnetically 'soft' and 'hard'.

Physicist-Writer
Drakkith said:
f the iron never magnetized, there wouldn't be a magnetic force at all between it and the magnet. It's only because the iron gets magnetized that it is attracted towards the magnet. Once the iron is magnetized by the magnet, it itself is now a magnet. Thus there should be no difference between a piece of iron magnetized temporarily and a piece of iron magnetized permanently in terms of the force of attraction, at least as long as the amount of magnetization is the same in both pieces.
Yeah, so i mean what happens to the strength of the magnetic field when the iron now becomes magnetized. Initially there's a magnetic field created by the magnet, and now the iron gets influenced by that field and becomes a magnet itself, and that's why it's attracted, there's now a magnetic force. But does that mean too that the overall strength of magnetic field is increased now? That's what I think I was trying to ask but was asking the wrong way, until you clarified further with this response.

There are three interdependent fields, the magnetic induction B, the magnetic field H, and the magnetization M. Using them interchangably and calling them all "the magnetic field" is likely to produce more confusion than clarity.

Physicist-Writer
Physicist-Writer said:
Initially there's a magnetic field created by the magnet, and now the iron gets influenced by that field and becomes a magnet itself, and that's why it's attracted, there's now a magnetic force. But does that mean too that the overall strength of magnetic field is increased now? That's what I think I was trying to ask but was asking the wrong way, until you clarified further with this response.
I'd like to say 'yes', but I'm not really an expert in this area. From a distance, you now how 2 magnets where you had 1 before, so I would imagine that the field becomes 'stronger' in some sense, but that's just a guess on my part.

Physicist-Writer
There are three interdependent fields, the magnetic induction B, the magnetic field H, and the magnetization M. Using them interchangably and calling them all "the magnetic field" is likely to produce more confusion than clarity.
True, I'm referring to the net magnetic field B, so the total field that now arises after the iron has been magnetized for example by the permanent magnet.

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