Naked Science Forum

Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: Hadrian on 07/12/2009 16:28:26

Title: Does gravity affect a magnetic field ?
Post by: Hadrian on 07/12/2009 16:28:26
Magnetic force v gravity

So I get a small magnet and hold it over a metal pin. At some point the pin appears to defy gravity and rises up to the magnet. 

If there was less gravity would it move sooner? 

What happens in zero gravity?


[MOD EDIT - HADRIAN, PLEASE PHRASE YOUR THREAD TITLES AS QUESTIONS. THANKS. CHRIS]
Title: Re: Does gravity affect a magnetic field ?
Post by: PhysBang on 07/12/2009 16:55:03
It would move sooner. There might be some small electromagnetic interaction between the pin and the table, but it wouldn't be significant next to the magnet you have. Since the pull of the magnet gets weaker exponentially, it wouldn't have an obvious effect on the needle until you moved it closer that a foot, I would guess.
Title: Re: Does gravity affect a magnetic field ?
Post by: Hadrian on 08/12/2009 10:58:17
It would move sooner. There might be some small electromagnetic interaction between the pin and the table, but it wouldn't be significant next to the magnet you have. Since the pull of the magnet gets weaker exponentially, it wouldn't have an obvious effect on the needle until you moved it closer that a foot, I would guess.

Interesting thanks.  I often imagined what you could do with a big amount Magnetic Force in outer space.  Perhaps pull the space station. LOL
Title: Re: Does gravity affect a magnetic field ?
Post by: lightarrow on 08/12/2009 13:00:55
It would move sooner. There might be some small electromagnetic interaction between the pin and the table, but it wouldn't be significant next to the magnet you have. Since the pull of the magnet gets weaker exponentially, it wouldn't have an obvious effect on the needle until you moved it closer that a foot, I would guess.

Interesting thanks.  I often imagined what you could do with a big amount Magnetic Force in outer space.  Perhaps pull the space station. LOL
Yes, but the magnet would be pulled down as well... [;)]
Title: Re: Does gravity affect a magnetic field ?
Post by: graham.d on 08/12/2009 14:56:35
I don't wish to be picky but the fall off of a magnetic field with distance is inverse square (not exponential). As magnets only occur as dipoles the fall off with distance would be faster (inverse cube if I remember correcly) but still not exponential. And it would never be zero so that in zero gravity the pin would move towards the magnet no matter how far away it was (allbeit very slowly if the magnet was a long way off). And, as lightarrow says, the magnet will start accelerating towards the pin assuming both are in free space although, assuming the magnet is of greater mass than the pin, by much less than the pin's acceleration.
Title: Re: Does gravity affect a magnetic field ?
Post by: PhysBang on 08/12/2009 15:23:00
I am assuming that the magnet is about the size of a refrigerator magnet. At even a couple of feet, I'm estimating that the pull on the pin would not be significant. This would be an interesting exercise to work out, though.
Title: Re: Does gravity affect a magnetic field ?
Post by: graham.d on 08/12/2009 17:26:29
It's difficult to calculate with a magnet without knowing how far apart the poles are and the strength etc. The question of zero gravity implies being not earth-bound and away from other fields. The question would be what is "significant" as the force between the pin and the magnet would never be zero. What you could probably say (if my memory of inverse cube law for a dipole is right) is that the force at 1 metre away will be 1 millionth of what it would be 1cm away. This probably isn't quite right because the inverse cube law only applies when the distance is much larger than the pole spacing, but you get the picture.
Title: Re: Does gravity affect a magnetic field ?
Post by: Hadrian on 09/12/2009 12:42:01
I wonder if there has ever been any experiment done on this in outer space?

and thanks everyone for sharing my interest in this topic.
Title: Re: Does gravity affect a magnetic field ?
Post by: Mr. Scientist on 09/12/2009 13:21:33
Magnetic force v gravity

So I get a small magnet and hold it over a metal pin. At some point the pin appears to defy gravity and rises up to the magnet. 

If there was less gravity would it move sooner? 

What happens in zero gravity?


In zero-gravity weight equals nothing. What is the equation for weight in conjugate respect to the mass in zero-gravity?

A little homework question i would like you to solve - it's not too hard. :)
Title: Re: Does gravity affect a magnetic field ?
Post by: vwilmot on 10/12/2009 10:03:15
 [:(!]
Magnetic attraction is not simple inverse square, and is not simple inverse cube.
If it was simple then that would certainly have been established before 1600 by William Gilbert.

Isaac Newton noted in Principia Book 3 Proposition 6 Cor.5 that magnetic attraction was not inverse square and that it often decreases with distance 'not in the duplicate but almost in the triplicate proportion of the distance'.

Magnetic attraction varies with differences in the shape and structure of magnets, as well as with their magnetic strength. And unlike other simpler forces, magnetism also involves other motion effects besides attraction like in compass motions - as see http://www.new-science-theory.com/william-gilbert.html (http://www.new-science-theory.com/william-gilbert.html).
 [:(!]
Title: Re: Does gravity affect a magnetic field ?
Post by: graham.d on 10/12/2009 16:54:08
Well I said it was from memory that, at distances from a dipole much greater than the distance between the poles, the force is inverse cube. So given the comment above, I checked and I was right. There are plenty of calculations on the web. Here is one:

http://teacher.pas.rochester.edu/phy122/Lecture_Notes/Chapter30/chapter30.html

Look at section 30.3

Magnetsim was not really well understood in the 16th century so referencing work from that time is probably not going to be as good as looking at what is known today. I agree that if close to the dipole the force is much more complex, hence the caveat.
Title: Re: Does gravity affect a magnetic field ?
Post by: Geezer on 10/12/2009 18:40:29
One potential "fly in the ointment". Where do we find this "zero gravity" thingy?
Title: Re: Does gravity affect a magnetic field ?
Post by: Hadrian on 11/12/2009 11:31:43
One potential "fly in the ointment". Where do we find this "zero gravity" thingy?

indeed
Title: Re: Does gravity affect a magnetic field ?
Post by: Mr. Scientist on 11/12/2009 13:41:19
W=Mg

If weight is dependant on the gravitational acceleration, then inspace the acceleration is zero compared to the force we experience on earth. If you fit the correct values into the equation, you will find your weight to equal zero.
Title: Re: Does gravity affect a magnetic field ?
Post by: vwilmot on 11/12/2009 16:17:26
 [:(!]
Graham.d you are basically right about a case far from the case being considered - 'I get a small magnet and hold it over a metal pin'.

And like almost everybody you seem to have not studied early physics much, it is of course widely assumed to be worthless these days though I am not so sure.
Title: Re: Does gravity affect a magnetic field ?
Post by: Mr. Scientist on 11/12/2009 16:18:44
[:(!]
Graham.d you are basically right about a case far from the case being considered - 'I get a small magnet and hold it over a metal pin'.

And like almost everybody you seem to have not studied early physics much, it is of course widely assumed to be worthless these days though I am not so sure.

How unfortunate then.
Title: Re: Does gravity affect a magnetic field ?
Post by: Geezer on 11/12/2009 17:41:18
W=Mg

If weight is dependant on the gravitational acceleration, then inspace the acceleration is zero compared to the force we experience on earth. If you fit the correct values into the equation, you will find your weight to equal zero.

Indeed W=mg, but are you sure g is zero?
Title: Re: Does gravity affect a magnetic field ?
Post by: lightarrow on 11/12/2009 19:45:06
[:(!]
Graham.d you are basically right about a case far from the case being considered - 'I get a small magnet and hold it over a metal pin'.

And like almost everybody you seem to have not studied early physics much, it is of course widely assumed to be worthless these days though I am not so sure.
Arbitrary assumptions.
You don't seem to have studied basic logic much...  [:)]
Title: Re: Does gravity affect a magnetic field ?
Post by: syhprum on 11/12/2009 21:52:01
If I use a long magnet so that only one pole has any effect on the pin does the inverse cube law still apply or does it revert to the inverse square law ?
Title: Re: Does gravity affect a magnetic field ?
Post by: lightarrow on 13/12/2009 13:09:14
If I use a long magnet so that only one pole has any effect on the pin does the inverse cube law still apply or does it revert to the inverse square law ?
~ the second one.
Title: Re: Does gravity affect a magnetic field ?
Post by: Mr. Scientist on 13/12/2009 13:11:24
W=Mg

If weight is dependant on the gravitational acceleration, then inspace the acceleration is zero compared to the force we experience on earth. If you fit the correct values into the equation, you will find your weight to equal zero.

Indeed W=mg, but are you sure g is zero?

Yes - this is why we are weightless in space.
Title: Re: Does gravity affect a magnetic field ?
Post by: Geezer on 13/12/2009 20:25:44
W=Mg

If weight is dependant on the gravitational acceleration, then inspace the acceleration is zero compared to the force we experience on earth. If you fit the correct values into the equation, you will find your weight to equal zero.

Indeed W=mg, but are you sure g is zero?

Yes - this is why we are weightless in space.

That's not true. Let's say we are in the space shuttle orbiting the Earth. We are apparently "weightless", but g is not zero. Earth's gravity continues to attract us and maintains us in orbit. If g suddenly became zero, we would start moving in a straight line tangential to our previous orbit and we would leave Earth behind.

OK, but what happens when we are far enough away from the Earth or the Sun for them to exert a meaningful gravitational force on us. Now we are moving in a straight line, so g is zero, right? Nope. That's not right either. Assuming we are still in our galaxy, we are still under the influence of its gravitational field, so g is still nonzero. Mind you, the radius of our orbit in this situation is rather large, so our path will approximate a straight line, but it is not straight, therefore g is nonzero.
Title: Re: Does gravity affect a magnetic field ?
Post by: Hadrian on 14/12/2009 13:38:25
James Oberg explains the phenomenon this way:

"The myth that satellites remain in orbit because they have "escaped Earth's gravity" is perpetuated further (and falsely) by almost universal use of the zingy but physically nonsensical phrase "zero gravity" (and its techweenie cousin, "microgravity") to describe the free-falling conditions aboard orbiting space vehicles. Of course, this isn't true; gravity still exists in space. It keeps satellites from flying straight off into interstellar emptiness. What's missing is "weight", the resistance of gravitational attraction by an anchored structure or a counterforce. Satellites stay in space because of their tremendous horizontal speed, which allows them — while being unavoidably pulled toward Earth by gravity — to fall "over the horizon." The ground's curved withdrawal along the Earth's round surface offsets the satellites' fall toward the ground. Speed, not position or lack of gravity, keeps satellites up, and the failure to understand this fundamental concept means that many other things people "know" just ain't so."
Title: Re: Does gravity affect a magnetic field ?
Post by: Geezer on 14/12/2009 17:13:21
Thanks Hadrian! I was beginning to think I might be going off my rocker. (Jibes, no doubt, will follow  [;D])
Title: Re: Does gravity affect a magnetic field ?
Post by: Mr. Scientist on 14/12/2009 17:36:39
No - he is wrong. There is no gravitational accceleration due to the planet earth in accordance to weight. If that where true, then we would be able to stand inside our space shuttles.

This is pretty much basic physics.
Title: Re: Does gravity affect a magnetic field ?
Post by: Mr. Scientist on 14/12/2009 17:38:50
Perhaps partially-right.

Not in the sense that we are fixed to the earth by a certain weight due to the earth's accelerational force. It's a matter of free fall.
Title: Re: Does gravity affect a magnetic field ?
Post by: Mr. Scientist on 14/12/2009 17:44:28
But i have made an error - i should never have used the term zero-gravity. I was actually referring to weight - that is weight measured ''or the aparent weight'' measured in the earth's astmosphere where the acceleration is measured against the surface of something.

ps. Zero-gravity is a very misleading term. I blame the OP lol
Title: Re: Does gravity affect a magnetic field ?
Post by: Geezer on 14/12/2009 20:10:31
Mr S - With all your "train of thought" posts, I don't really know what you are now saying.

Earlier you said that g for an orbiting body was zero. Are you now saying that is incorrect?
Title: Re: Does gravity affect a magnetic field ?
Post by: Mr. Scientist on 14/12/2009 21:09:10
I can't do this right now ok. I'm having a lot of problems.

Title: Re: Does gravity affect a magnetic field ?
Post by: Geezer on 14/12/2009 21:25:01
A "yes" or "no" would be sufficient.
Title: Re: Does gravity affect a magnetic field ?
Post by: Mr. Scientist on 15/12/2009 13:29:58
A "yes" or "no" would be sufficient.

Actually - at the time i was dealing with a police matter. So at the time, i could not suffice and bow down to your immediate requests.

g - as in the earths gravitational acceleration is according to the math zero even though the state of free fall in space is indestinguishable from the state of something falling in a state of free fall in air space. Though, when weight is conjectured g is a specific weight measurement we use for material bodies, not necesserily ones which orbit the planet earth, even though it ''can'' be correctly stated as so. It's a matter of which way one choses to look at what ''g'' actually means when weighing gravity upon the earths surface - not beyond the atsmospehere itself.

Title: Re: Does gravity affect a magnetic field ?
Post by: Geezer on 15/12/2009 20:07:27
Actually - at the time i was dealing with a police matter. So at the time, i could not suffice and bow down to your immediate requests.

I hope it was not a matter of too much gravity  [;D]

Quote
g - as in the earths gravitational acceleration is according to the math zero even though the state of free fall in space is indestinguishable from the state of something falling in a state of free fall in air space. Though, when weight is conjectured g is a specific weight measurement we use for material bodies, not necesserily ones which orbit the planet earth, even though it ''can'' be correctly stated as so. It's a matter of which way one choses to look at what ''g'' actually means when weighing gravity upon the earths surface - not beyond the atsmospehere itself.

I think your math is a little wonky there Mr S.  Gravity exerts a force on all orbiting bodies. The force of gravity does of course vary depending on the distance between the centers of mass of the attracted bodies. It's weight that is meaningless for an orbiting body. In that respect, it is "weightless". Weight can only be meaningfully measured on a body that is not actually being accelerated by gravity.

Being in orbit is little different than running fast then jumping off the ground. When we jump, gravity applies a force that accelerates us back towards earth. An orbiting body just goes so fast that it does not return to earth, but it is being pulled back towards earth by gravitational force in exactly the same manner.

There is one aspect of this that does tend to create confusion. Matter is attracted by gravity whether it is moving relative to the force of gravity or not. The force exerted can be measured in, for example, Newtons per kilogram. However, force/mass resolves to distance/time/time which is acceleration. This is fine when a body is in free fall because it is actually accelerating at that rate. But when it is stationary on the surface of the earth, the force of gravity is obviously not accelerating the body at all.

BTW, "microgravity" when used in the context of bodies orbiting earth is very misleading. There is nothing "micro" about it. The force is a bit less than it is at the surface of the earth, but nowhere near as small as "micro" would suggest.
Title: Re: Does gravity affect a magnetic field ?
Post by: Hadrian on 15/12/2009 20:13:12
I got an email from James Oberg today he said

"Thanks -- I'm glad the subject still inspires!!"


well i hope he enjoying the mature and supportive way we appere to work together here LOL

Title: Re: Does gravity affect a magnetic field ?
Post by: Bored chemist on 15/12/2009 21:43:50
A "yes" or "no" would be sufficient.

Actually - at the time i was dealing with a police matter.


Somehow, that doesn't surprise me.
Title: Re: Does gravity affect a magnetic field ?
Post by: yor_on on 26/12/2009 02:12:23
An orbit is in reality a free fall. The exact same fall you would have standing on a cliff trying to see if you too can fly :)

The idea behind a 'stable' orbit is just that, to make your 'speed' relative the object you are orbiting so fast that you keep 'falling' around it without either going inward or outward. In reality there are no really 'stable orbits' that I know of though?

--------

And vwilmot. That was a cool link, I liked to read about that guy William Gilbert, albeit reading some more pages you seem to have some rather unorthodox conclusions. But it was interesting.
Title: Does gravity affect a magnetic field ?
Post by: syhprum on 27/12/2009 20:02:08
The term 'microgravity' can of course be applied to the force that the astronaut feel attracting him to the structure of the vehicle, this of course very small.
Title: Does gravity affect a magnetic field ?
Post by: yor_on on 31/01/2010 22:33:46
Isn't weightlessness just a 'free fall' following a path of less resistance?
As Langranian points will be a special case where your 'free fall' is inhibited by resistance at all 'sides'?

==
Sorry, missed that I already had...
Whatever :)
Title: Does gravity affect a magnetic field ?
Post by: Hadrian on 08/03/2010 00:00:58
so did we get and answer or what?  [???]
Title: Does gravity affect a magnetic field ?
Post by: yor_on on 08/03/2010 13:10:05
It depends on how you mean in fact.
In the caption you ask  "Does gravity affect a magnetic field"
No, not as I know.

Inside the thread you ask something else.

"So I get a small magnet and hold it over a metal pin. At some point the pin appears to defy gravity and rises up to the magnet. If there was less gravity would it move sooner? "

Yes.

But that's about invariant mass and the invariant mass of the object 'creating' the magnetism. Although, it's a very messy 'field' I agree :) It depends on how you define gravitation I think, if you believe it to be a 'energy' interacting, or if you see it as 'SpaceTimes geodesics'.

Let's reformulate the question a little.

Can I by adding invariant mass 'change/bend' a magnetic field? Assuming ...no motion... whatsoever.. inside those invariant masses (think permanent magnet versus a nonmagnetic invariant mass (without any electromagnetic field at all), if possible:) and also between their 'frames of reference', them being 'at rest' versus each other? Just by adding more nonmagnetic invariant mass?

Title: Does gravity affect a magnetic field ?
Post by: Hadrian on 10/03/2010 22:49:54
Well that cool thanks  [:)]