Electromagnetic Rail gun and a circular track

[aeroseek]

Two parallel electromagnets situated symmetrically on either side of the straight section of an oval track propel a wheeled trolley along the track, so that the trolley is in continuous motion, as long as the current is supplied to the electromagnets.

Is this workable? Does the entry and exit speeds of the trolley have any effect on the continuity of motion of the trolley?

 

[A.T.]

Is this workable?

Yes. A as long you supply electrical power, it will move. It's just a different type linear motor.

 

[aeroseek]

Does this article and diagram correctly describe the operation of this device?

http://www.21stcentech.com/headlines-u-s-navy-test-electromagnetic-railgun/

The reason for using an electromagnetic rail gun is that much higher projectile can be obtained than by using permanent magnets, for example if the electromagnetic railgun can accelerate a projectile from 0 upto 6,000 kmh as opposed to the 0- 40 kmh or so we see on Discovery Channel for example, or those common experiments on You Tube using permanent magnets.

 

[Nugatory]

Does this article and diagram correctly describe the operation of this device?

No. That article describes what a colleague of mine (who built one in his garage - that's a different story and less exciting than it sounds) calls a "real" rail gun. You will notice that although it is powered by electromagnetic forces, it doesn't use electromagnets as you're describing.

(The currents and voltages involved are also extremely dangerous)

 

[aeroseek]

I am intrigued - can you tell me where I can get information on how this railgun really works?

 

[A.T.]

I am intrigued - can you tell me where I can get information on how this railgun really works?

http://en.wikipedia.org/wiki/Railgun#Basics

 

[aeroseek]

http://en.wikipedia.org/wiki/Railgun#Basics

Thanks. So you are saying Wikipedia is a reliable source of info in this case.

 

[Borek]

Good enough for starters.

 

[aeroseek]

OK, so the thread started out by saying:

Two parallel electromagnets situated symmetrically on either side of the straight section of an oval track propel a wheeled trolley along the track, so that the trolley is in continuous motion, as long as the current is supplied to the electromagnets.

This works

Imagine the electromagnets accelerate the trolley from 2 m/s to 5 ms/ sec and the trolley ends up constantly moving through on the track.

Now if you replace the word "electromagnets" by "permanent magnets" even though the permanent magnets have the exact same accelerating effect
2 m/s to 5 ms/ sec, the system will not work.

Two parallel permanent magnets situated symmetrically on either side of the straight section of an oval track propel a wheeled trolley along the track, so that the trolley is in continuous motion... no current needs to be supplied to the permanent magnets.

I am not sure I understand how a device will stop working when its motive force is replaced by an exact equivalent motive force, however since when permanent magnets are used the system is considered to be in perpetual motion, so there is no point discussing this.

Note that no discussion has been made as to the strength of the permanent magnets, that is, if they are strong enough to propel the trolley for 0.99 of a circuit ( not perpetual motion ) or half a circuit or more than half.

I leave it to all who read this to think, experiment and make up their minds for themselves.

I do not intend to discuss anything that suggests perpetual motion as this seems to be not the forum to do so.

Thanks to all ( including admin/moderators)

 

[Borek]

You are right about the system with electromagnets and the system with permanent magnets being equivalent (assuming these are magnets of exactly the same strength), you are just missing how it works in general.

"Current is supplied to electromagnets" means just that - electromagnet being equivalent to the permanent magnet.

Note that there is a difference between "continuous motion" and "continuous acceleration".

Trick is, energy conservation doesn't allow such system to produce energy - so we don't have to analyze every possible setup in hope one of them will work differently, as energy conservation tells us - they all don't work.

If you tell me "67894637892647890 is a prime number" I don't have to waste time factorizing it to know you are wrong - it has zero at the end, so it is divisible by 2 and 5. It is the same with any system made of magnets that can be proposed - it won't produce energy, so there is no need to waste time checking where is the error in someones reasoning, if it reasoning gives conclusion that the energy is produced.

 

[A.T.]

This works

What works is an "electromagnetic railgun" (as stated in the title and described in the Wiki link) that propels something within on a circular track.

I am not sure I understand how a device will stop working when its motive force is replaced by an exact equivalent motive force,

It's not an exact equivalent. Permanent magnets create a static magnetic field. The magnetic field created by the railgun rails is not static, it changes with the motion of the projectile:

 

[Borek]

The magnetic field created by the railgun rails is not static

To clarify - while the magnetic field in railguns are not static, you can use electromagnets to generate a static magnetic field. There is no contradiction between different statements in this thread, as they don't refer to identical setups/situations.

 

[A.T.]

To clarify - while the magnetic field in railguns are not static, you can use electromagnets to generate a static magnetic field. There is no contradiction between different statements in this thread, as they don't refer to identical setups/situations.

To clarify further - When the electromagnets generate a static magnetic field, they cannot propel anything continuously on a circular track, just like permanent magnets cannot. The original post didn't specify what kind of magnetic field the electromagnets generate, and the title implied it's dynamic like in a rail-gun.

 

[aeroseek]

The analysis of this problem is not only to do with magnetism but also with the way physics problems are analyzed on this forum. Regardless as to what works or not, and whether it would imply perpetual motion or not, like some of the other queries that I have raised, once the reason is known, we can all gain some satisfaction that we have enlarged our knowledge store.

So to clarify even further, let's reduce this to a 'black box' problem:

By the way, the oft - requested video on You Tube on the permanent magnet rail gun is at this location: www.youtube.com/watch?v=Vo2-Qb3fUYs

Two steel balls each on separate identical tracks roll into a two covered tunnels running over each respective track one containing an electromagnetic rail gun and the other an arrangement of permanent magnets as shown in the rail gun experiment on you tube.

1) Can we tell by observing the entry and exit speed of the steel ball, whether the device within the tunnel contained an electromagnetic rail gun or a permanent magnet rail gun?

2)If no, is there anything in either arrangement that will make it impossible for the steel ball to roll in at a particular speed and roll out at a higher speed?

3) Is it possible that in both tracks the balls roll in at 0.2 m/s and roll out at 1 m/s, depending on the strengths of the device in the tunnel assume each device can be adjusted before hand to give this result?

 

[A.T.]

Two steel balls each on separate identical tracks roll into a two covered tunnels running over each respective track one containing an electromagnetic rail gun...

What exactly do you mean by "electromagnetic rail gun". What is described on the Railgun-Wiki and picture above? Or just some electromagnets generating static magnetic fields?

 

[aeroseek]

Whatever arrangement works to accelerate a steel ball down a track. If the Railgun-Wiki works then that is fine.

 

[Borek]

Whatever arrangement works to accelerate a steel ball down a track. If the Railgun-Wiki works then that is fine.

As far as I understand you can't reproduce railgun described in wiki with static magnets.

 

[A.T.]

If the Railgun-Wiki works then that is fine.

Ok, let's go with that and call it EMRG, while the other is PMRG.

1) Yes, the speeds will decay over several loops in the PMRG case, until it will get stuck. And of course you can tell the difference by the cables providing electrical power in the EMRG case.

2) Yes, if begin & end of the tunnel are arbitrary, you can find a section where the object speed increases, if it manages to reach the begin.

3) Yes, you can match the speed up for the first loop. But in the PMRG case the second loop will not have the same speed at begin.

 

[Bandersnatch]

Here's a video of a permanent magnet arrangement reflecting the linear one from the video posted earlier by aeroseek:


As can be seen, when the initial impulse decays below what is sufficient to overcome the retarding influence of the next magnetic arrangement, the projectile stops.
As the projectile stops, an oscilating motion can be observed, indicating that the magnets are not explicitly propelling the projectile forward, but attract it to a specific point on the track, accelerating the projectile before it gets there, and decelerating it as it passes the point.

If you build an electromagnetic coil gun*http://en.wikipedia.org/wiki/Coilgun) to accelerate the projectile, you can turn the coils off before they start retarding the projectile. You can't turn the permanent magnets off.

 

[A.T.]

As the projectile stops, an oscilating motion can be observed, indicating that the magnets are not explicitly propelling the projectile forward, but attract it to a specific point on the track, accelerating the projectile before it gets there, and decelerating it as it passes the point.

Yes. For the arrangement in the video there could be several such points (local potential minima).

If you build an electromagnetic coil gun*http://en.wikipedia.org/wiki/Coilgun) to accelerate the projectile, you can turn the coils off before they start retarding the projectile.

Similarly in EM-railgun, the current and thus magnetic field disappear, when the projectile leaves the rails.

 

[aeroseek]

"1) Yes, the speeds will decay over several loops in the PMRG case, until it will get stuck. And of course you can tell the difference by the cables providing electrical power in the EMRG case."

Is everyone agreed on this? There was a suggestion earlier in another thread that since the magnet would take a long time to lose its magnetism - I believe the exact time was "zillions of years" this would constitute perpetual motion.

Also, any guesses on how long this thing will run? Days. Months, Years? Will make quite a toy.

 

[A.T.]

Also, any guesses on how long this thing will run? Days. Months, Years?

Not any longer than without the magnets, given the same initial energy and friction in both cases. See video below.

 

[Borek]

There was a suggestion earlier in another thread that since the magnet would take a long time to lose its magnetism - I believe the exact time was "zillions of years" this would constitute perpetual motion

If memory serves me well that was an attempt at rationalization of your earlier, mistaken statement. Garbage in, garbage out.

 

[A.T.]

If memory serves me well that was an attempt at rationalization of your earlier, mistaken statement. Garbage in, garbage out.

I was wondering if demagnetization of a permanent releases any energy at all, or if it actually requires an input of energy. When you consider a simple model of multiple aligned magnets, you have to put energy into de-align them. Is that also true for the elementary magnets in a metal?

 

[Borek]

I wonder if magnetic hysteresis doesn't give hints at what is happening and what to expect (random jab, I can be completely off).

 

[Vanadium 50]

I was wondering if demagnetization of a permanent releases any energy at all, or if it actually requires an input of energy.

It requires an input of energy,

 

[aeroseek]

Not any longer than without the magnets, given the same initial energy and friction in both cases. See video below.

I have seen the video - it is an unsuccessful attempt at building a PM powered motor. The device does complete part of a circle, maybe if the magnets at the point where it stops were removed it would not stop ? But that is beside the point.

I thought we already established that the trolley would complete several circuits before stopping? If it first enters the PM magnet section on the track at 0.2 m/s and exits at 2 m/s then if it completes a circuit of the track and enters the PM magnet section again at say 0.1 m/s - due to friction - it will again be forced forwards by the PM magnet arrangement to complete at least one more circuit? Surely it depends on the strength of the PM section or the distance of the PMs from the trolley, as well as friction?

In your opinion does this "SMOT" work, and does it violate any laws of physics? I know it has been discussed before, but I am just asking if it works.



If it does work, let's not discuss whether the steel ball can be made to make circuits using a track. I just need to know the possible input and exit speeds of the steel ball, that's all. I can make the connection that a steel ball rolling on a track can be made to keep going round and round if given a small push by hand, for example, duplicating the effect of the PM arrangement.

 

[Borek]

Over unity devices don't work for the reasons that were already mentioned many times.