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Normally how long this repel process will stop?anuttarasammyak said:Two magnets repel and repel force which depends on distance keeps the same forever. Motion of magnets would die due to other factors e.g., friction.
cel123456 said:Normally how long this repel process will stop?
The magnetic force behaves like the gravitational force. The force of attraction of a mass to the Earth (its weight) stays the same as long as other things don't change. Two permanent magnets will experience the same force between them until 'something' changes. They don't 'get tired', if that's what you are suggesting.cel123456 said:Normally how long this repel process will stop?
Damped oscillation as lectured here might be of your interest.cel123456 said:Normally how long this repel process will stop?
anuttarasammyak said:Damped oscillation as lectured here might be of your interest.
See Paleomagnetismcel123456 said:common sense, how long magnet will stop repel each other?
The oldest rocks on the ocean floor are 200 mya – very young when compared with the oldest continental rocks, which date from 3.8 billion years ago. In order to collect paleomagnetic data dating beyond 200 mya, scientists turn to magnetite-bearing samples on land to reconstruct the Earth's ancient field orientation.
My late wife usually deferred to my EM knowledge except for animism and 'tired magnet' theory. One day a garnet decorated refrigerator magnet popped off the 'fridge and rolled across the kitchen floor.sophiecentaur said:{snip}Two permanent magnets will experience the same force between them until 'something' changes. They don't 'get tired', if that's what you are suggesting.
I see your point. @cel123456 do you share it with @sophiecentaur?sophiecentaur said:The Energy in the Oscillation will decay but the force pulling the pendulum bob towards Earth at the equilibrium position won't.
sophiecentaur said:Not really in this discussion. The Energy in the Oscillation will decay but the force pulling the pendulum bob towards Earth at the equilibrium position won't.
sophiecentaur said:Haha if you are going to be pedantic then explain, if the force goes to zero, why the bob doesn’t just float away. It’s the RESTORING force that goes to zero. I wrote what I wrote with some care.
sophiecentaur said:the force pulling the pendulum bob towards Earth at the equilibrium position won't.
etotheipi said:Basically I'm saying your original statement is correct only if by "force" you mean the weight only and not the resultant, and I suspect this is what you actually mean.
sophiecentaur said:Imo you were trying to play the pedantry game (great fun, of course) and chose the wrong playing field.
Assuming you are thinking of permanent magnets, the answer is that the magnet holds electrons spinning about their own axes. If the spin axes are alignedcel123456 said:As we know the magnet will stop to repel each other after some time, is there any formulae to calculate when it will stop? From common sense, how long magnet will stop repel each other? 1years?
rude man said:electrons spinning about their own axes.
Electrons have 'spin' and they are charged. That causes them to behave like small electromagnets with a Moment Dipole Moment. But the 'current' in these electromagnets cannot decay. That's a consequence of Quantum Mechanics.weirdoguy said:Um, how?
As I understand it, only the spinning electrons at the material's surface produce the magnetic field. Interior electrons cancel each other.sophiecentaur said:Electrons have 'spin' and they are charged. That causes them to behave like small electromagnets with a Moment Dipole Moment. But the 'current' in these electromagnets cannot decay. That's a consequence of Quantum Mechanics.
In most materials, most of the time, the total of electrons with one spin equals the total with the other spin so most materials cannot be permanently magnetised.
Can that be correct? Where have you read that?rude man said:As I understand it, only the spinning electrons at the material's surface produce the magnetic field. Interior electrons cancel each other.
What you point out does not negate the idea of surface currents.sophiecentaur said:Can that be correct? Where have you read that?
If you take a permanent magnet and break it half way, there will be two new poles. Also there is an internal field all the way through.
sophiecentaur said:Electrons have 'spin'
If I may respond to @sophiecentaur 's post:weirdoguy said:Well, yes, they have spin, but since when this means that they are spinning around their own axes?
And so do the bands of alternating magnetisation in the widening gaps between some tectonic plates. These alternations are due to the new ferrous material coming to the surface and cooling down, aligned with the Earth's magnetic field at the time and then remaining magnetised. The magnetic stripes are evidence of when the Earth's field flips (every couple of hundred thousand years) and the records go back many cycles.Keith_McClary said:
This is true but it takes us from the 'theoretical idea; to the practical reality. It's not the Field that gets 'tired' in old headphones; it's the energy levels associated with the dipole orientation in old fashioned magnetic materials. At room temperature, there is a finite probability of the occasional flip to a lower energy state. All materials can be expected to change over time - even when that change corresponds to longer than the possible life of the Universe.tech99 said:The permanent magnets in old earphones slowly lose power over many years. It is also normal practice to use a "keeper" on a permanent horse shoe magnet to preserve its strength. The external field of a magnet is in a direction to slowly demagnetise the magnet.
Yes. Although there can hardly be a "formula" for this as the decay rate will depend on the elements involved and the detailed structure of the magnet. I think you'd need to do measurements involving an oven to produce a curve for each particular material.mitochan said:The law of entropy increase in statisc or thermal mechanics would work here. The ordered spins of molecules tend to be randomized which leads zero magnetic field. The ordered motion of charges e.g. electric currents in wire would be dissipated which also leads to zero magnetic field.