A Puzzling Physics Problem

not the answer

When it is below the magnet, there are two forces.

a) Gravitational

b) magnetic.

Depending on which force is stronger the iron ball remains/ moves up.

In thsi condition, there is a negative work done (in magnetic force) and positive (with reference to gravitational)

Hence the two potential energies in this conditions are simply exchanged and nett energy of the system remains same, with possibility of a bit of kinetic energy.

Since the F_mag > F_gra , when the ball hits the magnet, it is likely to impart a bit of kinetic to it also just to maintain the energy balance.

If you said the energy of pulling up the iron ball come from the Magnetic field , then we would expect the magnetic field of the magnet will weaken after a number of times of pulling. But we know magnetic strength of magnet will not decrease after some exertion by the magnet, otherwise , all permanent magnet motor will go kaput after a few round of revolution.

So, this is puzzling part : work is done in pulling up the ball, you can keep doing this, the magnetic strength is not reduced, there is no input of energy , so, where does the energy come from ?

There is something I miss here !!

You might ask why gravity doesn't 'run out'

When you make a magnet you align the naturally random poles of the crystals. Without that aligning it is not 'magnetic'. But aligned the energy is 'coalesced'' into a uniform energy.

I.e. it exists, aligned, or not.

Does that help?

the energy was fed to the iron, a large amount of it to make it a permanent magnet!

the magnetic domains on the iron do the rest, once they got aligned due the electric therapy they received, and now they live happy being metal attractors!!!

A given magnetic field stores a specific amount of energy. This field changes when the iron ball enters and gets pulled up to the magnet. The overall energy stored in the altered magnetic field is reduce by the amount of gravitational potential energy added to the iron ball. Neglecting the small amount of energy lost to friction, drag, and material deformation the system energy remains the same.

Going by your explanation, do you think , if I bring a big iron ball to the magnet, the magnet will lose all its magnetic strength immediately, due to a big mgh energy has been expended ?

No! If a big volcano collapses and falls to the earth, does the earth lose all its gravity?

In order to lift an object against the Earth's gravity, you must add energy to the system (object + Earth). Whatever forces originally lifted that volcano to its high position added energy to the mass of the volcano (or more correctly, to the Earth + volcano system). When that object returns to a lower level (closer to the center of the Earth), some (but not all) of that energy can be recovered.

Same thing with magnetism. When you allow a magnetic object to move toward a permanent magnet, the system (object + magnet) looses energy, some of which can be recovered. When you pull a magnetic object away from the magnet, YOU are adding energy to the system. Some (but not all) of that energy can be recovered while allowing the object to 'fall' back toward the magnet.

Back to my question specifically, if you allow a number of iron balls to be lifted one by one, there will come a point the magnet will cease to be a magnet because all its magnetic field energy has been used up ? Is this the case?

I miss something here.

From the entire discussion, I feel that you are uncomfortable that the laws of thermodynamics appear to be violated. What happened to the mgh?

Please shift your attention to how the magnet is fixed above the ball. The mgh acts on this support, which either elastically or plastically (or partially both) deforms and the energy either gets converted to heat ( in the case of plastic deformation) or retained as stored potential tensile energy in the support.

Do this mental experiment. Imagine the magnet suspended from a spring. When the ball is pulled up the magnet is pulled down by an amount that exactly compensates the mgh.

When an object falls to earth, the earth RISES by a minuscule height that exactly compensates the mgh. The system remains in equilibrium.

What is apparently "missing" is the energy required to magnetize the ball (orient its atoms' spin in accordance with the external magnetic field). When the ball is pulled away from the magnet, the induced field is lowered by the increased distance and the energy stored in the ball magnetization is restored to the external field and ultimately to the magnet generating that field. The energy comes from the relaxation of the atoms' spin which in the non-magnetic material is in the natural minimum when disorientated, and is increased when close to the permanent magnet..

So there is no mystery there. However, the important question is what is going on within the space between the two objects, or how exactly does the field change the properties of space. This, I believe, has something to do with the so called "vacuum energy" or the "zero-point field", namely the orientation of the dipoles of complementary charged particle pairs which temporarily pop-up into existence from the underlying Planck's "half-photon" (h_bar×omega/2) field, owed to Heisenberg's uncertainty.

Let's see if I can explain it better.

The magnet itself does not lose energy. The energy is in the magnetic field around the magnet. The field changes in size, shape, and density when a single iron ball gains mgh and the magnetic field energy is reduced by that amount. When you remove the iron ball from the magnet, the magnetic field is restored to its initial configuration and energy.

If you continually add iron balls to your gedanken experiment, the magnetic field is eventually reduced to a point where no new iron will "stick" to the group. Theoretically you have just determined the amount of energy stored in the original magnetic field and it is the sum of all the potential energy now stored in the group of iron balls. When you remove all the iron, the magnetic field is once again restored to its original configuration and energy. No net energy is gained or lost.

Try this at home: Use a small permanent magnet to pick up a big pile of paper clips. At some point, no more paper clips will stick to the group. The energy of the original magnetic field is now stored in the potential energy of the paper clips. Remove all the clips and the energy is restored to the magnetic field around the magnet.

What many people don't understand is that magnets do not contain a large amount of stored energy. Magnets ARE very useful tools because we can use them to move electrons (generators) and we can use electrons to move magnets (motors).

Electromagnetic field theory was the largest weed-out course in my day and fields in general can be difficult concepts to grasp since we can't see them directly. Keep asking questions and eventually the little light bulb of understanding will begin to glow. Hope this helps

Your explanation seems to be the most likely .

So, going back to my post #11

Going by your explanation, do you think , if I bring a big iron ball to the magnet, the magnet will lose all its magnetic strength immediately, due to a big mgh energy has been expended ?

If you bring a big iron ball to a small magnet, the small magnet will lose it magnetic force immediately. I will do a small experiment to find out.

"Back to my question specifically, if you allow a number of iron balls to be lifted one by one, there will come a point the magnet will cease to be a magnet because all its magnetic field energy has been used up ? Is this the case?"

No. The constituents of atoms (protons, neutrons and electrons) contain a magnetic moment that is inherent to their nature and does not alter in any appreciable way until the particle is destroyed. As long as all of the atoms remain in alignment, the magnetic field will remain at a fixed strength. What happens though, is that over time the particles will randomize their alignment due to the encounters with other objects (your steel balls for example) and the field will be weakened. Eventually, all magnetized objects lose their magnetism even if they don't encounter other objects, simply because randomization (entropy) increases over time.

I believe the major force in the complete universe is entropy, this is the force that is trying to bring everything back into equilibrium, a singularity, Steven Hawkings. So when the ball is lifted by the magnet it is moving into equilibrium, when the ball is removed that equilibrium is disturbed, but still exists.

Regards JD.

Its like you buy a compression spring in compressed condition and when you saw it releasing obvious question arises where does the energy come from?

In the case of magnet as you are suggesting, throw bunch of balls under it and it will pull some of them and leave many, repeat the process again with the balance balls and now it will not pull any ball or at the most one or two, This mean energy stored in magnet is already consumed and there is no more energy left in the magnet to pull any more ball, Now you remove all balls from the magnet and the energy consumed to remove all balls from magnet will be stored again in magnet.

"In the case of magnet as you are suggesting, throw bunch of balls under it and it will pull some of them and leave many, repeat the process again with the balance balls and now it will not pull any ball or at the most one or two, This mean energy stored in magnet is already consumed and there is no more energy left in the magnet to pull any more ball, Now you remove all balls from the magnet and the energy consumed to remove all balls from magnet will be stored again in magnet."

You obviously never tried this or you would see that this assumption in false. As more material gets lined up and contributes to the field, the longer the reach. Try this one for example, use any magnet to pick up any object that is fairly light and able to be lifted up a couple of inches by the magnet. Now attach something like a nail or other massive object that can be magnetized to the magnet and try the same experiment. The magnet can now be much further away and still pick up the object. The field is enhanced by the extra magnetizable material.

Think twice before reaching on such conclusion and calling fact as false assumption. Balls will follow the least reluctance path in magnetic field and will wrap around the magnet not that balls will hang one under another.

Do you think this magnetic lift will gain more power as its catches more scarp or will it loose power?

Interesting example. I believe as additional parts are attracted and lifted, the attraction force is reduced based on the reluctance of the part's material and their distance from the magnet. As far as work and power goes, the attraction is similar to gravity (?) where the forces of the attraction vary as the distance from the source and there is no real net power to be extracted from the field without additional work input to the "system".

Welcome to CR4, Read it carefully on top. If you know something why dont you share for sake of creator?

To declare that there is no God is like saying the Earth is flat by looking at a pre-Colombus map of it. God may not be the God of the Jews, Romans, Vikings, etc., but it may be the energy from which all matter came from, and which has given life to that matter. Educated people know that there's a lot of things they don't know, and so shouldn't dismiss anything as being absolutely impossible.

I think you read the post incorrectly, he did not say, "there is NO GOD!"..he said

Societies, or certain more imaginative individuals within those societies, have for many millennia created (FALSE) gods for the things they could not yet understand.

Educated people now understand fire, water, lightning, etc., so those gods are no longer needed.

....meaning that it was MAN that created FALSE Gods to worship, as I highlighted.. and as we now understand FIRE, we as MAN have no need for the FALSE GOD of FIRE.

I see no reference or statement saying there is no GOD..period! Do you?

'...You are not theoretical physicists. They deal with the why........ If you want to know the truth, ask Jesus, the creator....'

.

Help me out here, I am confused. Are you saying all theoretical physicists are Christians doing God's work? Or are you saying Jesus was a theoretical physicist (i thought theoretically he was the Jewish carpenter zombie).

.

I look forward to your explanation.

.

Oh, i almost forgot to ask...do you believe dinosaurs once roamed the earth?

"If you want to know the truth, ask Jesus, the creator."

Not sure which version of the Bible you read, but in mine is says..

In the beginning when God created the heavens and the earth, the earth was a formless void and darkness covered the face of the deep, while a wind from God swept over the face of the waters.

Then God said, 'Let there be light'; and there was light. And God saw that the light was good; and God separated the light from the darkness. God called the light Day, and the darkness he called Night. And there was evening and there was morning, the first day.

So using my God given intelect, I'd say that God is the creator NOT Jesus, who depending on which religion you follow, is either;

The Son of God, or

The First Prophet, and Mohamed (Peace be upon Him) is the second

and from the Koran, Chapter 2. AL-BAQARA with reference to the creation

002.029

Y: It is He Who hath created for you all things that are on earth; Moreover His design comprehended the heavens, for He gave order and perfection to the seven firmaments; and of all things He hath perfect knowledge.

P: He it is Who created for you all that is in the earth. Then turned He to the heaven, and fashioned it as seven heavens. And He is knower of all things.

S: He it is Who created for you all that is in the earth, and He directed Himself to the heaven, so He made them complete seven heavens, and He knows all things.

My apologies to followers of other faiths for not quoting other passages from other religions, the quotes I have given are to highlight my point and not to promote one faith above another.

well spoted!!

You are half right , the field is modified when the iron balls are added. But it still has the same amount of energy or magnetic strength it is just that the field is distributed over a larger area there fore the force per unit area is weaker.

Seems that this is the answer, thank you for your contribution.

GA

Please consider these actions as cyclic.

In each case the energy stored in iron ball = mgh = E1

The work done to pull the iron ball from the magnet is = E2.

always

E1 < E2.

As per the law of energy, It holds good.

Called Potential Energy due to Pulling Force of Magnet

Bravo88:Why do you accept objects could have a potencial energy (grav.) like an airplane in the air but not the earth+moon system? just because men put the airplane overthere (i know you didn't say that).I feel you will accept for explanation men spent energy manufacturing a magnet ordering the small ones existents previously in the material, a part of it could be tranfered to the ball iron wich is magnetized along its rise up, etc.But, i feel the real issue here as in the other thread about energy in fluid flow have the same psychological root:you feel energy becomes from an human effort or some like that.-

The energy comes from the original energy spent by you in magnetizing the permanent magnet. If you do not use a permanenet magnet and instead use an electromagnet, then you can measure the energy used for pulling up the steel ball, when the magnetizing current changes during the pulling operation.

Yes, I think this is a simple and good experiment to prove. GA.

But this energy, (the energy required to magnetize a permanent magnet) is tiny compared to the energy required to pull balls away from that magnet repeatedly.

Here is an experiment you can do: Measure the force required to move a 1" ball away from a strong magnet. Measure this force at increments of distance. Sum these incremental forces over a distance of 2 inches (50 mm) to calculate the amount of work done per ball retraction. Multiply by a conveniently large number, such as 100,000,000, (the number of times a permanent magnet in a motor does similar "work" in a short period of time, such as a day.)

Measure the energy required to magnetize the magnet at the factory. I will be a very tiny amount compared to the energy consumed in repeatedly pulling the ball away from the magnet.

"The energy comes from the original energy spent by you in magnetizing the permanent magnet."

It is highly unlikely That the OP magnetized his own permanent magnet. It is much more likely that the magnet was magnetized at a factory. That is where the energy came from.

Then of course, if you trace back, the electric energy used to magnetize the magnet at the factory almost certainly came from one or more nuclear power sources (either a nuclear power plant, the sun, or a combination of the two). Coal, gas, petroleum, etc. are simply stored solar energy.

A lot of red herrings being offered in this thread, and I think this is another

I.e. the energy used to create alignment is expended in creating alignment.

It's the alignment of the existent normally random micro-poles in the micro structure that makes it 'magnetic' as gross entity.

How many you successfully align, and manage to keep aligned, determines the strength and 'permanence' of a magnet.

An insight to this is adding, or subtracting, bar magnets, does not 'add or subtract Gauss'

Another, in the reverse scenario, is 'magnetic iron' is 'soft' to allow 'flipping of poles' to transmit magnetic flux, but not become 'permanent'.

Similarly your balls become attracted because their micro-poles are substantially free to align.

This alignment will attract another ball.

There is a limit to the number of balls attracted (against gravity) as the subsequent balls are not 100% efficient 'magnetic iron', and the eventual mass exceeds the attractive force.

To understand this more fully, research why some things are magnetic and most are not.

"I.e. the energy used to create alignment is expended in creating alignment."

I fail to see why this is a 'red herring'! The energy required to magnetize a magnet (to create the alignment) can be measured quite readily. The product of the voltage, current, and time used in magnetizing the magnet is the energy expended. If the voltage is measured in Volts, the current is measured in Amperes, and the time is measured in seconds, then the energy is in units of Watt-seconds. There are conversion factors to change the result into any other unit of energy you may prefer.

May be the case for electromagnets - but across the range of permanent magnets much depends on alloying - which is not much to do with a ratio of 'watts in' to 'Gauss out'.

Can you show me a significant permanent magnet that was not originally magnetized using an electromagnet? It took electric energy to magnetize that permanent magnet, and there is a relationship between the magnetizing energy and the resulting permanent magnet field strength, although that relationship is far from linear and quickly reaches a limit.

Be very careful to use appropriate units.

Quite obviously I have upset you. Sorry about that. Maybe this will help

I saw nothing there that helps. Unfortunately the article did not (unless I missed it) say anything about how those rare earth magnets obtain their magnetism. Unless I am mistaken, they are magnetized by electromagnets. If I am mistaken please show me how they are magnetized.

I think you are correct (no red herring).

The normal state is random magnetic domains and no external magnetic field. A specific amount of energy is needed to align the random domains to create the permanent magnet. Not all the applied energy is stored as some domains do not remain in the desired alignment (see remanence or retentivity ).

Adding/subtracting permanent magnets may not change the "magnetic flux density" [Gauss or Tesla], but it does change the total flux and the total energy stored.

The OP probably does not need (but may wish) to investigate magnetism in materials at the microscopic/atomic level. Some study and discussions like this can be a good start in understanding the basic concepts at the macroscopic level.

Some suggested reading for anyone interested...
http://en.wikipedia.org/wiki/Magnet
http://en.wikipedia.org/wiki/Magnetic_field
http://www.oersted.com/magnetizing.PDF
http://www.madehow.com/Volume-2/Magnet.html

They are magnetized by an electromagnet while the alloy is above their Curie temperature. The field from the electromagnet is maintained as the alloy is allowed to slowly cool below the Curie temperature. Now during all of this time all of the power being released by the electromagnet is dominated by the heat from DC resistive heating of the coil. The energy stored in the magnetic field will be constant and can be calculated by W_m=1/2L*I². With L being the inductance of the electromagnet with the alloy core inside the electromagnet. In the classical Physics sense this stored energy came from the initial turning ON of the electromagnet only.

You could insist that you need an electromagnetic field to 'magnetize' (meaning cause alignment of the micro poles in a material). You can quantify that energy input.

But, as said, it has no real relevance to the energy resulting from alignment.

Equally, the energy exerted in striking of a material aligned to the earths magnetic field, thus 'magnetizing' it, can be quantified, but has no particular relevance to the 'work' that magnet can do, or the longevity of the magnetism.

It is much like the energy to stand a column vertical, has no real relevance to the work the column then does.

Much as I said in post 10; "You might ask why gravity doesn't 'run out'"

The poles preexist at an atomic level - you are just aligning.

Anyhow, have a read of the following. Bear in mind;

"The more physically correct description of magnetism involves atomic sized loops of current distributed throughout the magnet" (from)

• 2.6 Magnetic materials
• 8 Microscopic origin of magnetism

I fail to see why this is a 'red herring'! The energy required to magnetize a magnet (to create the alignment) can be measured quite readily.

It is a red hearing because the energy required to magnetize a magnet is infinitesimally small in comparison to the energy required to repeatedly lift iron balls.

Learner42 said in post 44, a direct response to the OP, that "The energy comes from the original energy spent by you in magnetizing the permanent magnet." "The energy" to which he refers is the energy mentioned in the original post: that required to endlessly lift balls, one after another, for decades. The magnet was magnetized by watt-seconds, but the work done is measured in kilowatt-hours.

Work is done on an iron ball by the magnetic field. Same work is needed to extract an iron ball from the field. For 1-∞ iron balls, NET work is zero, NOT [kW-hours]. Actual energy stored in the magnetic field is quite small, which is why the magnet can only lift small number of iron balls at the same time.

BINGO! GA for you.

The ability of the magnet to lift the first ball comes from the magnetizing energy. All the rest of the energy comes from whatever force(s) extract the balls from the higher strength portion of the field at the surface of the magnet.

Agreed.

It think this will be more understandable for the OP, who, if I read his original post correctly, seemed to think that each lift of a ball from the floor represented some quantity of energy: force x distance or mgh. The magnet can do millions of such lifts. If one ignores the fact that each ball has to be pulled away to allow the magnet to lift the next ball (assuming, for convenience it can only lift one at a time), then it seems that the magnet is supplying this large amount of energy.

The comment that the magnetizing energy is the source of this energy (the kilowatts) that the OP was writing about, is misleading, I think. I think that is why it was characterized as a red herring. The kilowatts come from whomever is willing to pull the balls off the magnet, just as the energy in a waterfall comes from the mechanisms required to evaporate the water (to lift it to a higher potential energy).

Hi K Fry,

you provided the best answer.

The puzzle to me was I thought the magnet can do unlimited number of lifting of the iron balls.

Now it is clear that you can only do so provided you pull away the iron ball from the magnet , by so doing , you restore back the magnetic field.

Thanks, I'm happy to help.

I note that every post that disagrees with the demonstrably fallacious idea that a permanent magnets energy is directly related to the energy expended in alignment - has now been marked OT.

This has been a very interesting thread, revealing the distinctions between scientists (as physicists) and engineers, with an admixture of "other."

A scientist keeps an open mind to theory, but usually has working opinions (unless totally theoretical - never met one).

An engineer has the ability to produce correct working answers, but prefers a good formula to a good theory.

Much of the difference of opinion expressed above would be eliminated by close quantification. For example, I routinely magnetize new tools I want to be magnetic, and demagnetize tools I do not want to be magnetic, and I do not use electromagnets. Magnetic fields are vector fields, unlike gravity, and can show variations in polarity and shape. (look at Earth's magnetic field and magnetic compass)

How many balls the magnet can (or will) pick up seems to be an issue. How much energy is involved is another issue. How strong a field is needed to magnetize a permanent magnet is another. Several formulas have been presented, but there are no numerical questions to answer.

Anyway, GA for tried and true #22.

Permanent magnet material formulation IS critical in determining remanence, coercivity, and thermal stability of the end product, but the premise that the energy stored in a permanent magnet (PM) is present PRIOR to the magnetization process is FALSE.

If such a premise were true, it would be good news for magnet manufacturers, bad news for magnetizing equipment manufacturers, and disastrous news for Science in general because it would violate the First Law of Thermodynamics.

Magnetization is accomplished either by electrical impulse (capacitive discharge through a solenoid) OR by mechanically placing the PM "blank" into an existing permanent magnetic field. The latter requires work to remove the newly formed PM from the field and part of that work becomes the energy stored in the newly created magnet. Regardless of magnetization method, enough energy must be applied to align normally random magnetic domains.

In all cases, more energy is expended during the magnetization process than is stored in the resulting PM. The total energy stored in a PM is finite and relatively small. Some of the energy stored in a PM can be used to do a limited amount of work, but work must be put back into the system to restore the initial energy. The energy stored in a PM during magnetization IS the energy used by the PM to lift the iron balls mentioned in the original post. That energy is returned to the PM by the work done to remove the iron balls from the PM.

There is no mystery here since the fields, forces, and work (energy) can be mathematically modeled & calculated quite accurately.

http://www.madehow.com/Volume-2/Magnet.html
http://www.britannica.com/EBchecked/topic/356975/magnet/4447/Magnetization-process
http://www.oersted.com/magnetizing.PDF
http://www.intemag.com/pdf/MMPAPMG-88.pdf
http://www.m-pulse-asia.com/english/technology/magnetizing_process2.html
http://www.femm.info/wiki/PMEnergy#ref5

FYI... Permanent magnets are NOT practical sources of energy or energy storage devices.

Modern battery ~ 300 [W-hr/l] = 1.08 [MJ/l] (ref1) (http://www.allaboutbatteries.com/Battery-Energy.html) (Sorry! Link no longer available.)

Modern magnet ~ 260 [kJ/m^3] = 260000 [J] / 1000 [l] = 260 [J/l] (ref2)

but the premise that the energy stored in a permanent magnet (PM) is present PRIOR to the magnetization process is FALSE

enough energy must be applied to align normally random magnetic domains.

If the first is FALSE, then why are you doing the second?