# Does it take long for magnets to respond to each other, and is it dependent on their separation?

danielhaish
so I toke three magnet, two smell magnet and big one so the big one is attractive both of small onces so it order like -(+-)+ .
I toke the small magnet close to the edge of the range magnetic and lift it so the magnetic field is preventing it from falling because the magnet is trying to flip while the gravity is pulling it down. but when it touch one of the magnet they both started shivering up and down ', in difference speed and the wireds part is that when I pushed them harder they keep routing in the same speed and when they about to stop they start changing their moving direction from up to down afaster (compare it to wave it like the frequency is higher) time but still move in the same speed till they stop. my explanation is that the magnet take time to response the change of locatation so the magnet fall and then the magnet response stronger because the magnet closer so the movement keep going .
and the other magnet start moving because the when the magnets get closer it made it attract faster . but the weird thin is that the two magnet effect each other quiet fast.

this is link to my record experience it may looks like the magnet reject each other but they actually attract each other so the magnet trying to flip . as you can see in the video when I touch one magnet the other start moving . it also works with one magnet .

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Delta2

danielhaish
and also when one is up the other is down I think ?

Mentor
You will have to mechanically isolate the magnets from one another, otherwise vibrations can be transmitted through the table.

danielhaish
danielhaish
You will have to mechanically isolate the magnets from one another, otherwise vibrations can be transmitted through the table.
I kind of have an idea of how the vibration move because I made another experience which I put small magnet far enough to big magnet so it won't attract to the big mange and then add another magnet behind it and it made the the magnet stronger so the small magnet did attract it so the power of the magnet add together I think

Mentor
I kind of have an idea of how the vibration move because I made another experience which I put small magnet far enough to big magnet so it won't attract to the big mange and then add another magnet behind it and it made the the magnet stronger so the small magnet did attract it so the power of the magnet add together I think

Nice, but you should be doing the experiments with the same setup. Here, the middle magnet appeared much smaller that in the first case. The distances between the magnets also appear to the different.

You would do the same with the setup in the OP. Compare the reaction time.

danielhaish
danielhaish
Nice, but you should be doing the experiments with the same setup. Here, the middle magnet appeared much smaller that in the first case. The distances between the magnets also appear to the different.

You would do the same with the setup in the OP. Compare the reaction time.
I made this I had to chage the size of the magnet a bit any way I didnt saw notice able delay thanks

Mentor
The electromagnetic interaction works at the speed of light. That's about 0.0000000003 seconds delay in your setup. Of course you can't measure that.

sophiecentaur and danielhaish
when the magnets get closer it made it attract faster
Mainly stronger. As @mfb notes, the propagation speed is so fast, that you cannot notice it here. The delay is because your oscillators are weakly coupled, so it takes some time to transfer enough energy from one to the other to make the oscillation visible.

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danielhaish
Gold Member
Mainly stronger. As @mfb notes, the propagation speed is so fast, that you cannot notice it here. The delay is because your oscillators are weakly coupled, so it takes some time to transfer enough energy from one to the other to the other, to make the oscillation visible.
Are we sure that a magnetic field propagates at the speed of light? We cannot measure that unless we vary its intensity to create an envelope, and then we have an EM wave. The magnetic field seems to be just a stationary store of energy.

davenn and danielhaish
Mentor
Are we sure that a magnetic field propagates at the speed of light?
A magnetic field is literally part of light.
And yes, of course we have, particle accelerators routinely work with rapidly changing magnetic fields for example.
The magnetic field seems to be just a stationary store of energy.
A static magnetic field doesn't propagate at any speed because it's static by definition, that's trivial. A non-static magnetic field will necessarily have an electric field component, that's unavoidable.

Gold Member
Summary:: please watch the video it explain the summery

so I toke three magnet, two smell magnet and big one so the big one is attractive both of small onces so it order like -(+-)+ .
I toke the small magnet close to the edge of the range magnetic and lift it so the magnetic field is preventing it from falling because the magnet is trying to flip while the gravity is pulling it down. but when it touch one of the magnet they both started shivering up and down ', in difference speed and the wireds part is that when I pushed them harder they keep routing in the same speed and when they about to stop they start changing their moving direction from up to down afaster (compare it to wave it like the frequency is higher) time but still move in the same speed till they stop. my explanation is that the magnet take time to response the change of locatation so the magnet fall and then the magnet response stronger because the magnet closer so the movement keep going .
and the other magnet start moving because the when the magnets get closer it made it attract faster . but the weird thin is that the two magnet effect each other quiet fast.

this is link to my record experience it may looks like the magnet reject each other but they actually attract each other so the magnet trying to flip . as you can see in the video when I touch one magnet the other start moving . it also works with one magnet .

Each magnet is behaving as a mechanical resonator I think the two magnets are vibrating in quadrature. This occurs when we have two resonators which are weakly coupled together. So I think the magnets weakly interact via the magnetic system, but there is no observable delay caused by the magnet in this case.
I don't think an iron core will introduce a delay due to the speed of light unless we draw power from one end, as with a transformer, in which case we seem to have a magnetic waveguide. Clearly, energy cannot travel at infinite speed. If there is no load, there is only a standing magnetic wave on the core and no delay should be measured. The same applies to magnetic fields in free space as far as I can see.

danielhaish
alan123hk
Thank you for sharing.

This is a very interesting complex electromechanical system. There must be information passing through the electromagnetic field at the speed of light because we can see the obvious force and energy interaction between the left and right magnets.

The oscillation frequency of the system should be determined by the distance between the magnets, the strength of the magnetic field and the weight of the magnets.

Due to the different initial conditions and the distances from the center magnet, it can be clearly seen that the oscillation amplitude of the right magnet is greater than that of the left magnet.

As for the derivation of the actual motion equation, the cooperation of electrical engineers and mechanical engineers may be required. 🤔🙄

danielhaish and Delta2
Mentor
Getting all the prefactors right is complicated but the basic idea is simple. The equilibrium position has both outer magnets at an angle. If we consider small oscillations only then each magnet is a harmonic oscillator. The small interaction between the magnets couples these harmonic oscillators.

With suitable coordinates we get the potential energy ##U(x,y) = \frac 1 2 (x^2 + y^2) + c(x-y)^2## for some small c and the kinetic energy is simply ##\frac 1 2 (\dot x^2 + \dot y^2)##.
Introduce ##u=\frac{1}{\sqrt{2}}(x+y)## and ##v=\frac{1}{\sqrt{2}}(x-y)## and we get ##U(u,v)=\frac 1 2 u^2 + (\frac 1 2 + 2c) v^2## while the kinetic energy is still ##\frac 1 2 (\dot u^2 + \dot v^2)##. We now have two decoupled harmonic oscillators corresponding to synchronized (\\ - //) and anti-synchronized (\/ - /\) oscillation of the two magnets with slightly different frequency. The motion will be a superposition of them.

This is basically the same as two coupled pendulums, shown e.g. here.

alan123hk and A.T.
Gold Member
I think oscilating magnets are the same frequency. I cannot see beats as described. In the case of the same frequency they vibrate in quadrature.

alan123hk
alan123hk
I also can't see any obvious beat phenomenon in the video clips, let alone any intermodulation. But I still carefully counted how many times they swung by themselves. 49 times on the left and 51 times on the right. This proves that there are indeed two independent harmonic oscillators, but their frequency difference is very small.

In addition, I noticed that the oscillation amplitude of the left magnet gradually increases from small to large. I guess this means that energy will gradually transfer from the oscillator on the right to the oscillator on the left. However, at the same time, I do not rule out that this is related to the beat phenomenon, and after calculating the time relationship more carefully, I found that the possibility of being related to the beat phenomenon is indeed not low.

The system may become more complicated, especially when its oscillation amplitude increases to certain extent, the effects of nonlinearity and intermodulation must be considered.

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danielhaish
danielhaish
I also can't see any obvious beat phenomenon in the video clips, let alone any intermodulation. But I still carefully counted how many times they swung by themselves. 49 times on the left and 51 times on the right. This proves that there are indeed two independent harmonic oscillators, but their frequency difference is very small.

In addition, I noticed that the oscillation amplitude of the left magnet gradually increases from small to large. I guess this means that energy will gradually transfer from the oscillator on the right to the oscillator on the left. However, at the same time, I do not rule out that this is related to the beat phenomenon, and after calculating the time relationship more carefully, I found that the possibility of being related to the beat phenomenon is indeed not low.

The system may become more complicated, especially when its oscillation amplitude increases to certain extent, the effects of nonlinearity and intermodulation must be considered.
I read about the beat phenomenon and it should make the movement bigger and smaller by time right? for example in sound it would be loud sound and then soft sound and then loud sound again

danielhaish
I also can't see any obvious beat phenomenon in the video clips, let alone any intermodulation. But I still carefully counted how many times they swung by themselves. 49 times on the left and 51 times on the right. This proves that there are indeed two independent harmonic oscillators, but their frequency difference is very small.

In addition, I noticed that the oscillation amplitude of the left magnet gradually increases from small to large. I guess this means that energy will gradually transfer from the oscillator on the right to the oscillator on the left. However, at the same time, I do not rule out that this is related to the beat phenomenon, and after calculating the time relationship more carefully, I found that the possibility of being related to the beat phenomenon is indeed not low.

The system may become more complicated, especially when its oscillation amplitude increases to certain extent, the effects of nonlinearity and intermodulation must be considered.
in the beginning they routing at same speed but then it change and the first magnet it also routing three times before the second one

alan123hk
alan123hk
I read about the beat phenomenon and it should make the movement bigger and smaller by time right? for example in sound it would be loud sound and then soft sound and then loud sound again

Yes, it should be like the situation you described. However, due to the energy loss, the oscillation in the video quickly disappeared, so it is difficult to determine whether the beating was actually observed. We have not seen the continuous cyclic change of the oscillation amplitude from small to large and then from large to small.

in the beginning they routing at same speed but then it change and the first magnet it also routing three times before the second one

Because of your reminder, I also noticed this strange phenomenon.
In the beginning the frequency and phase of the two seem to be the same. After a while, the oscillation speed of the one on the right suddenly increased, and the relative phase of the two reversed rapidly. Before the video was about to end, their relative phase seem to be reversed again. Sorry, I have no idea how to explain this phenomenon at the moment. 🤔

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danielhaish
Mentor
I didn't include damping, which is significant here and makes both oscillations decrease over time. In this case the oscillation might die down before we got a full transfer of the oscillation to the second magnet. It's also possible that one of the magnets is more damped than the other.

vanhees71, danielhaish and alan123hk
danielhaish
so I made another experience which made it very clear to see(in slow monition) how one magnet movement ,getting longer while the other getting shorter and after while it switch so the the second magnet movement , ,become short again the first magnet movement become bigger it happened three time till the magnet stops .

in the video we can see that after I push the right magnet down it have more energy then the left magnet but then it slowly switch . and then switch again and again
watch till the end in slow monition .
and I draw the magnet force in each position of the magnets. the first draw it the force diagram of two magnet when one is rotating

and the second is diagram of three magnet

this draw can't explain why the magnet power getting stronger and weaker over and over so my guess is that it send some kind of wave that telling the magnet the it angle change and it change from both side so on one side we getting that the power of the magnet is getting stronger and on the other weaker . and then it switch , till it stops because the energy lots . this is actually like beats because it magnets have small difference frequency because they are not in the exacts same distance from the big magnet. so in one magnet when the movement become bigger in other it become weaker becuase they are in two difference location . and their wave interferer because when one magnet make the middle magnet stronger the other make it weaker .
so thanks everyone I finely understand why it happing I also find it very interesting to try following the forces and it help me understand magnet force a lot it also

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Mentor
this draw can't explain why the magnet power getting stronger and weaker over and over
It doesn't. The forces between the magnets only change minimally as function of their angle. The exact distance to the central magnet is irrelevant, too - you could use anything else to keep them in a position where small forces can move them.
The small distance-dependent force between the outer two magnets is sufficient to produce the motion your video shows - the motion I derived in post #13. Simple input, somewhat complex result.

danielhaish
It doesn't. The forces between the magnets only change minimally as function of their angle. The exact distance to the central magnet is irrelevant, too - you could use anything else to keep them in a position where small forces can move them.
The small distance-dependent force between the outer two magnets is sufficient to produce the motion your video shows - the motion I derived in post #13. Simple input, somewhat complex result.
but if you look at the all video you would se that it change back after servel times

but if you look at the all video you would se that it change back after servel times
This is normal behavior for coupled oscillators, where one is released in equilibrium and the other displaced from equilibrium. See video at 0.50 min:

danielhaish
danielhaish
This is normal behavior for coupled oscillators, where one is released in equilibrium and the other displaced from equilibrium. See video at 0.50 min:

ok now i see it

alan123hk
The behavior of coupled oscillators is really great.
We can show the same phenomenons by simulating a coupled electrical circuits interact magnetically by mutual induction.
For example, the following simulation result shows the energy exchange of the coupled oscillators, and the oscillation gradually disappears due to energy loss.

After several simulations, I found that the energy exchange frequency is proportional to the coupling coefficient and natural frequency of the two LC oscillator circuits.

danielhaish and A.T.