The Reactionless Space Drive? 301
waimate writes: "This New Scientist article describes some physics that is claimed could be the basis of a new space drive, and a reactionless one at that.
Our current knowledge of physics requires that a space craft throw most of itself away at high speed in the opposite direction to get anywhere, and this is why the Millennium Falcon won't exist any time soon.
A drive that doesn't depend on reaction mass would change all that. But is this it? The article seems to sidestep the obvious flaw." Or flaws, maybe.
This is really something for audiophiles (Score:1)
This, along with those oxygen-free speaker cables and a good tube amiplifier, would be the makings of a top-notch stereo, I think.
The problem would be the liquid He delivery truck that would have to come by every week; that could get expensive!
Just imagine how much better they'd sound!
A different electromagnetic drive (Score:1)
Reactionless??? (Score:1)
Astonished at New Scientist (Score:2)
From the article, it appears simply to be a high-tech version of the trick where you can propel yourself forward in a boat, or on some kind of wheeled cart, by moving slowly in one direction and then quickly in the other. The slow movement is not sufficient to overcome static friction, and nothing moves, while the rapid "jolt" does overcome friction and the boat or cart moves.
In other words, the whole effect depends on friction, and would not work in space. This is one of the oldest and commonest kinds of erroneous or fake perpetual motion or reactionless propulsion systems.
Steve Linton
Re:Maybe (Score:3)
Assymetric magnetic field. It sounds kind of kooky... they're making it for a brief period of time, but if such a thing were to be created for an extended period of time, a force could be generated just by being in the presence of any magnetic field, or any object which responds to magnetic fields.
They'll probably find out that either it is a wobble and not a shudder, or it will turn out to be in a random direction.. just like all the other quantum weirdness... Sort of like propelling yourself off Browninan motion... only magnetically. It looks neat under a microscope, but it would never work.
But I'm just guessing based on a reporter's interpretation of a brief interview with a scientist.
Re:A Severe Strain on the Credulity (Score:1)
Friction! (Score:1)
If you take advantage of friction, then you can actually get somewhere without touching anything other than the chair.
If you jolt quickly and then return to your original position slowly you've got a chance of getting somewhere, but good luck doing this in space.
Steve
Re: What law of Conservation of Energy (Score:5)
That's about the best concept I could get out of the article as well. Of course, this poses two problems:
actual design for reactionless drive (Score:3)
You have two counter-rotating flywheels bouncing along their axis of rotation forward and back in the ship. As they reach each end, they are accelerated in the opposite direction. As the flywheels are moving forward, increase their rate of spin, as they are moving backward, decrease their rate of spin. Since mass increases with velocity, the flywheels will have a higher mass as they are being accelerated backward than they will have as they are being accelerated forward. So you will accelerate forward.
Admittedly, it's not quite feasible, but it does show that a reactionless drive doesn't violate any physics. Yes, it does violate Newtonian physics, but that's because Newtonian physics is only an approximation to reality (and so might relativity, but a more accurate one).
If we actually understood what gravity is, we might be able to get some interesting reactionless (did Clarke just make that term up?) propulsion methods out of it. I'm thinking along the lines of making space curve like it would if there were a mass there, but whereever you want it to. Assuming thermodynamics, this would take a lot of energy, but it might be more efficient then just dumping burnt propellant out the back. Of course, this is probably impossible.
BTW, can anyone point me to a real discussion of how to build a fusion ramjet? It's a staple of a lot of sci-fi, but I'm curious how you keep from getting slowed down by collecting the hydrogen.
Same idea, slightly modified (Score:2)
I've thought about this for a while, even named it the 'Squid' drive in my own head. Move the magnetic fields to the outside, and they would provide protection from other hostile things in space. Unfortunately, I'm not rocket scientist or physicist, have no ties to NASA, and have not idea how to even begin to explore the idea any further.
So I just lamely post to
Weird Fun With Propulsion (Score:5)
Here's an example:
After I testified before the House Subcommittee on Space on my participation in the passage of a couple of laws to reform NASA's rather nasty attitude toward private launch services [geocities.com] I was pretty close to being out of money. Civic responsibility will do that to you if you don't watch it. Even so, a company whose rocket technology I liked was on the ropes -- a couple of weeks from closing their doors. The CEO gave me an impressive sounding position with the company, offered me a percentage in the company and I maxed out my credit flying around to see what I could do to help salvage the business with no guarantee of compensation.
The first day I arrived at HQ, a strange call came in to the CEO. Some guy claimed to have been referred by NASA because he wanted to find out how to obtain certain kinds of permits that the company had obtained. It turns out the guy wanted a permit to let a device he had made go into space. He said he had constructed a high power vibration stimulator as a diagnostic aid in his business, which was vibration isolation in some mechanical systems, and the damn thing malfunctioned. The problem is this particular Damn Thing, when it malfunctioned, started vibrating off to the side of the table and then it fell off -- but before it hit the floor, it turned in mid air and went up at an angle, hitting the ceiling of his shop where it hit so hard it left a dent in the metal conduit -- and it didn't just bounce off and fall to the floor, it stuck there until he unpluged the infernal contraption.
OK, well the obvious questions were asked like: "Was the conduit a feromagnetic material?" etc. "Are you sure it actually accellerated up to the ceiling or did it just jump up and somehow stick there?" -- you know, the standard Skeptics Society stuff.
This character got my curiousity, not having ever run across one of these conservation-law-violating-sonofaguns before, so I took one of his phone calls and started asking him innocent questions -- like, "How many tests have you run on the device since that time? Have you taken any quantitative measurements? What are the numbers? What did you to do get these numbers?" etc. The interesting thing was he gave me two sets of numbers from two tests, with different weights attached, he said he conducted on a playground with a fishing line attached to the thing to pull the plug on a cellular phone battery at a given height. The numbers he gave were distance traveled vertically vs time. In one test the calculus told me his upward force was less than in the other run by a big margin. So I asked him if he had changed anything else between the two runs other than adding the weight to one of them. He said no. So I asked him to describe his test procedure very carefully. He went through the process verbally, and at one point he said he "turned the variable resistor down until the thing started to lift off -- then I backed off". "Was the resistor in the same position both times?", I asked. "I don't think so because the heavier test run required more power."
Oh, gee whiz -- here is a guy who is not only imagining he ran a levitating device straight up in the air from a playground, but he fabricated results that were inexplicable except from an error in his experimental procedure that he himself seemed not to have thought about. He also told me that on the third run he had some friends of his with him to help and the thing lifted off but then exploded leaving a "line of metallic powder across the playground asphalt". This is either one hell of a smart sociopath playing mind games or he is a covert operative or he is some sort of genius at dreaming things up on the spot that even his conscious mind couldn't have fabricated or he is, in some important sense, telling the truth.
I admit it -- he had me hooked. I invited him to dinner and even though he was a couple hundred miles away, he drove his company truck up to meet me. I won't say what the company name was, because that would give a bit too much information away but it was a company name that was like a double-entendre or pun on his activities that reflected both his mundane business and this weird business of levitating infernal devices -- just the sort of the thing that your dream state would make up and Jung would analyze for you or maybe something that Jaques Vallee would report in one of his weirder "encounter" reports or maybe something that some covert operative would do to mess your mind up or maybe something a complete psycho would do because the little man in his head told him to. So anyway, I had dinner with him and he seemed genuinely worried when I told him that if this was real, he should take precautions by placing a disclosure with an trusted accounting firm to be put in the public domain upon his death or disablement. I don't think he thought I was going to kill him but he could pick up from me that I thought he should be more cautious.
So now what? OK, so he says he is going to build another version of it, because he thinks he knows the principle of operation, but he wants it to be lower power and lower frequency so it doesn't explode and hurt someone. He tells me how his experiments are going but he never seems able to get the original, unequivocal, levitating performance -- all his reports are closer to the rest of the legendary reactionless drives that always end up with marginal effects.
Finally, I tell him to send me a video tape of the thing either accellerating upwards or in a pendulum test and if he doesn't I won't be interested in talking to him any more, but if it shows an unequivocal force, I'll fly him to SV to talk to guys with some capital. He sends me a video tape. It is a short tape with some sort of noise on it. A friend of mine said it had been degaussed but with some sort of external magnetic field -- not by a tape recorder. So I call the inventor and tell him it really isn't OK to send me an erased tape. He seems at first incomprehending and then a bit afraid but then composes himself and starts speculating on how it might have been degaussed in transit. So he says he'll send me two tapes, one via UPS and one FedEx. I never received any packages, his phone is disconnected and I never hear from him again.
To wrap up the story, sort of, he did tell me the electric motor make he used, so I went to an electric motor place -- an old one that had been around since the early 60s. I asked for the specific motor and the proprieter turned around to the assistant and said "Do you remember that guy from the Apollo program at NASA Ames back in the 60s who was building the flying saucer? Where did we order that motor from?"
OK, that's enough weirdness for now...
What type of electric motor? (Score:2)
Re:Newton outlawed this type of thing (Score:2)
The law of Conservation of Energy (Score:2)
So, essentially... (Score:2)
It's only logical that scientists try to bend (or even break) the laws of physics, since they can't make a 400-ton spaceship that can channel the power of a supernova out of their tailpipes.
Mass change drive (Score:2)
Consider this thought experiment: e=mc^2. Now imagine a substance that can withstand increadible heat w/o undergoing a phase change. When it is very hot, it's mass is greater than when it is cold. Now:
The thing is, the spacecraft gains more forward momentum in step 2 than it looses in step 4.
That wound, of course be very inefficient due to all of that heat radiating away, but it simplifies the explaination. In practice, the mass would be inside a cylinder made of the same substance and would transfer it's heat (by radiation) to the cylinder wall. A heat pump (almost entirely UNLIKE the one that heats a house no doubt) would transfer it back in step 1.
Now, consider the magnet again. Imagine if it accelerates away from the matal block very quickly (for a very short time), and returns to rest position slowly. It has more mass when it is moving away than when it slowly returns. In this case, it would produce no net acceleration for the spacecraft (since it would still have it's large mass when it decelerated), but the spacecraft would 'judder' forward slightly further than it would move back when the coil returned to rest position.
In both cases, I keep wanting to find that missing bit of reverse momentum that leaves the spacecraft vibrating uselessly in place, but I just don't see it!
Re:There is already a "reactionless" drive (Score:2)
This is not true. There have been several solar sail prototypes flown that demonstrated this exact concept. A gyroscopically stabilized spacecraft can use an angled solar sail to change orbits around the earth just as well as it could in solar orbit.
Your implication is that solar sails are little more than dandelion seeds blowing on the solar wind. They're much more useful (and navigable) than that.
Re:actual design for reactionless drive (Score:3)
There is no reason to believe that a reactionless drive is possible at all. With that said, it may be quite possible to build spaceships with drive systems that would be considered reactionless by todays standards. Space is not actually empty. Although it is almost devoid of matter, it does contain magnetic and gravitational fields. It may be quite possible that we could learn to push on those fields to create motion.
Think of it this way: For a long time people did not know what a vacuum was, and didn't really know what air was. After all, it's pretty much invisible. If you didn't know that air existed, and believed that we were surrounded by empty space, how would a propeller-driven airplane work? Forgetting that air was understood long before thermodynamics, the airplane would appear to be a reactionless drive. After all, it moves around without anything to push on!
On the same note, it may be possible to build spaceships that create motion by pushing on the fabric of the universe itself. By todays standards, they would behave like a reactionless drive. But, that's just because we don't understand how to push against "empty" space.
As for ramjets, the answer to your question is yes, you would get slowed down by the collecting of the hydrogen. The hope is that the power you gain by fusing the hydrogen would be powerful enough to overcome the drag of collecting the hydrogen. Just like your car. The air creates a lot of drag on your car as it moves through it. However, your car is able to take some of that air into the engine, combine it with gasoline, and create enough motive force to overcome the wind resistance. At least, up to a point. Same thing with a ramjet. Or a turbojet engine on an airplane.
Re:Weird Fun With Propulsion - Saucer at Moffett (Score:2)
So maybe this little bit of wierdness is explained by the mundane.
Re:Newton outlawed this type of thing (Score:2)
1. The earth has a big magnetic field.
2. We can easily create big electromagnets with symmetrical magnetic fields.
3. Since the magnetic fields are symmetric, we can't use them for propulsion, or we would all be flying around in magnetically propelled cars already.
4. This potential new discovery of an asymmetric magnetic field gets around the problem of #3 by letting us build an asymmetrical magnetic field that will push against the earth's magnetic field, thereby producing propulsion.
5. They have to switch it on and off super fast to keep the field asymmetric.
Personally, I suspect that when the magnetic field collapses it will push in the opposite direction, thereby negating the effect. But maybe if you spin the magnet so it points the opposite direction when you turn it off...
I hope that somebody with a really strong understanding (like, a PHd grad student) of electromagnetic fields posts a big explanation in here somewhere.
Torrey Hoffman (Azog)
Re: Nah.... Maybe not. (Score:2)
When you turn on a magnet, electrically conducting objects will have to encompass the magnetic field. This induces a current. If the electrically conducting object is superconducting the electricity that will flow will completely cancel the magnetic field, and the electric current will continue to repell the magnetic field until something external happens. You can balance a superconducting piece of material above a magnet using this effect.
If you have a non-superconducting piece of iron, and you turn a strong magnet on, the object will jolt. This is a force between the magnet and the iron. So the magnet will be repelled by the iron and vice versa. Nothing mysterious. Nothing that will drive a spaceship.
Some guy saying that "there is unresolved physics" does not make me dismiss a century of well-verified physics.
Roger.
Re:Orbital Mechanics anyone??? (Score:2)
Gravity drops off by a square root the farther away you get from center of mass. Therefore, the 200 or so miles you gain can be used for your advantage. And there is nothing that limits you from using a 'space elevator' as a giant magnetically fired gun a few hundred miles long.
You're right about Sol's gravity well though. A space elevator doesn't do much for that.
Reactionless drive in General Relativity (Score:3)
In practice, it's difficult but not inconceivable. The effect gets stronger with the cube of the vibration rate. You need a very fast vibration, and experimentally it's really hard to accurately measure force on something vibrating that fast. So experiments so far have been somewhat inconclusive. The interesting thing is that there's no new physics postulated here--it's all a natural consequence of general relativity.
what a load of crap (Score:2)
Re:Maybe (Score:2)
Return of the Dean Drive/Davis Drive!
Search on Google [google.com] for "Davis Stine reactionless" and you'll find an entry into all of this wonderful world.
Summary: Davis and Stine maintain that there's a 3rd derivative force. Normally this balances out; but in transient circumstances, you can get it to show itself. Their best demo was a mechanical gadget that had an unexplained 3 degree phase angle.
Essentially, it's changing the system "before" the reaction force gets there. I don't know about this; if you think about physically long objects, Relativity would seem to prevent a reaction in less than twice the end-to-end light time - so there might be something.
Henry Troup
Re:It won't work. Physics says so. (Score:4)
As a practicing particle theorist, let me tell you what you got right and what you got wrong (more right than wrong!):
You cannot prove that a scientific theory is the correct description of the universe as we observe it...you CAN disprove a theory by showing that it conflicts with experiments. You CAN prove that a scientific theory is logically correct, but that doesn't prove that it is physically correct.
Quantum mechanics HAS been confirmed time and time again, but we ALREADY KNOW that QM is incomplete, just like we know that Newtonian Mechanics is incorrect (the point particles of quantum mechanics have been replaced by the quantized fields of Quantum Field Theory). QM is, however, "accurate enough" for almost all purposes where Newtonian Mechanics fails, and in the correct domain of application (anywhere where the corrections from QFT are small), QM is still used. I would go so far as to say that there are no practicing physicists who don't believe in the validity of QM; it would take some truly astonishing discovery to unseat quantum theory (it may happen, but I wouldn't hold my breath, just like I wouldn't hold my breath for any evidence that Newtonian mechanics ever fails on macroscopic scales).
There are four generally accepted forces (gravity, strong, weak, and electromagnetic), and there is a QFT model that "unites" the weak and electromagnetic force (and is called the electroweak force), although it isn't technically proper to call it a "single" force, but that is a nitpicking detail (having to do with the fact that the gauge theory describing electroweak interactions is not based on a "simple Lie group", but that is neither here nor there for purposes of this discussion...).
There is currently NO accepted quantum theory of gravity, although string theory provides a mathematically consistent physical theory which includes gravity. String theory (probably) has no currently testable consequences (we need a lot more work before we'll be able to ask questions that experiments have a real hope of answering).
While it WOULD be extremely surprising to discover a fifth force that operates over macroscopic distances, most (particle) physicists fully expect that there are additional microscopic forces that will be discovered in the next decade (supersymmetry is the sexiest these days, but there are many others: topcolor, technicolor, etc.)
QCD is well accepted as the proper description of the strong force, and is well tested at HIGH energies (not low). At LOW energies, it is a very hard theory to perform calculations in, and we have to resort to lattice monte carlo methods, which are computationally speaking, among the most demanding computer applications yet devised (for those with undergraduate physics backgrounds: you can't do a pertubation expansion in the low energy theory, as the coupling constant is a number of order 1, not a small expansion constant, and technically, we can't calculate what the fundamental degrees of freedom are in the low energy limit.)
Re:Weird Fun With Propulsion (Score:2)
And I don't see why the name of the business can't be given away...unless of course the poster is afraid of the men in black getting *him* too (which I guess isn't all that far fetched).
That's because this article is speculation (Score:3)
Where are you reading where the guy who proposed this idea is absolutely confident it will work? I read it more as if he was saying "hey, this is kind of cool. I'd like to see if it actually works out..."
The error is in their model's assumptions (Score:2)
The ultimate mistake in both cases can be summed up in a single sentence:
The are using quasi-static EM approximations when a fully dynamic model is required.
To explain:
Coming up with complete solutions to Maxwell's equations can be very complex for all but a few, relatively trivial geometries. However, many times, these equations (and their solutions) can be greatly simplified by making a quasi-static assumption. For example, if you can assume that the magnetic field is chaning sufficiently slowly that the dB/dt is negligible, the equations become much simpler to solve. The equations resulting from neglecting this term are referred to as the EQS (Electro-Quasistatic) model. Many basic circuit and, by extention, electric motor, equations are based on this model.
The problem is that in both of these cases, the changing magnetic field cannot be neglected and many (if not all) of the equations and assumptions they are running with aren't valid. Even people who understand the equations sometimes forget the key assumptions that led to them.
For example. Assume you have two identical perfect capacitors with capacitance C. You charge one of them up to voltage V. The other one has no charge. At this point the energy in the system is 1/2 CV^2. Now, connect these two capacitors (assuming there are no resistive losses). Half of the charge ends up in each capacitor. The total energy is
2 * new capacitor energy
2* (1/2 C * (V/2)^2).
1/4 C V^2.
Which is half of the original system energy. If there were no resistive losses, where did the energy go?
This ceases to be a mystery when you consider that acceleration of the charges in the capacitor is no longer negligible. An accelerated charge radiates energy. It is these radiative losses that explain where the missing energy went.
Yes, I know its not a perfect example but it illustrates the kinds of paradoxes you run into when the underlying assumptions of your model break down.
Re:Hard to believe (Score:2)
The "disturbance of the magnetic field" that he now wants to study might cause something like a magnetic eddy getting pushed out of the stable field. It would indeed be useful to be able to throw away energy for propulsion, if this can generate more power than throwing away photons with a laser.
Re:The law of Conservation of Energy (Score:2)
Mind you, I'm not throwing the Law of Conservation of Mass and Energy out, just noting that if you're going to be objective about it, you'll have to admit that science does NOT provide absolute truth: it instead provides working models of reality with a very high degree of reliability
Re:Maybe (Score:2)
Re:has nothing to do with this (Score:2)
Re:It won't work. Physics says so. (Score:2)
If noone believes it will work, it'll never be tried and become a self-fulfilling prophecy.
- Steeltoe
Re:Newton outlawed this type of thing (Score:2)
-josh
(posted with mozilla 0.6)
Re:has nothing to do with this (Score:3)
The magnetic field is created by applying a large current to the coils. Then, a large current applied to the rails. The resulting "short" circuit vaporizes the conducting layer on the projectile producing a conductive plasma.
The projectile is the propelled down the "barrel" of the rail gun by both the expansion of the plasma but more so by the resulting Loretz forces that are result of the interaction of the electrical discharge and the magnetic field. This force is perpendicular to the magnet field and direction of the current flow and can be quite substantial. It is this force that accellerates the projectile to a very high velocity. Damage to a target is primarily because of the kinetic energy of the projectile strike the target.
The military examined rail guns in the 80's. There was talk of "electric" ships that contained rail guns and lasers at the height of the Reagan "Star Wars" era. The problem with rail guns is they produce a very flat trajectory making them useless for over the horizon applications. Reducing the velocity of the projectile would reduce the kinetic energy of the projectile thus requiring heavier projectiles or explosive projectiles.
Another problem with early generation rail guns involved alignment of the rails. The forces produced in a rail gun often destroyed the rails or knocked them out of alignment. Thus, early generation RGs were limited in their ability to achieve sustained firing rates. I read a few years back that this problem had been corrected. Haven't heard much about rail guns since.
But, the approach of this "juddering" engine and a rail gun at not similar at all. And, until somebody proves otherwise, rail guns are stil confined to the laws of Newtonian physics. Hence, RGs have one hell of a recoil. That is why they were planned for use on ships and tanks as they are the only vehicles massive enough to absorb the recoil. Even the mighty IOWA class battle ships were pushed sideways several feet in the water when she fired her guns broadside.
RD
Re: What law of Conservation of Energy (Score:2)
We have bigger fish to fry than that. What about all those damned anti-environmental children who build sand castles on the beach? Don't they realize that their castles add friction to the tide and thereby slow down the moon? We can't just sit back and let this irresponsibility go on forever!
---
There is already a "reactionless" drive (Score:3)
It's not a reactionless drive per se, but solar sails do not have to carry around their reaction mass.
I still think... (Score:2)
...big ping-pong balls would work best. (and yes I am aware that something along those lines already exists)
A slight digression here, but has anyone ever imagined a network where ping-pong balls were used to comunicate data. If you could get it to run on solar wind (sorta like that fancy blowdryer trick) I bet you could make a near perpetual mechanical space computer. And ping-pong balls would be so easy to ship into space!
Good god, 3h46am and not even bothering to log on as an AC.
Re:Newton outlawed this type of thing (Score:2)
Would people just get over it, repeat after me, 'there is no such thing as a free lunch'.
Now, I am not at all amazed that slashdot picked this up.
-josh
Re:Weird Fun With Propulsion - Saucer at Moffett (Score:2)
It's embarassing, because the AvroCar [spectranet.ca] in the 1950s used the same idea and actually flew. But it wasn't stable. The AvroCar guys knew they needed automatic stability augmentation, but early 1950s control technology wasn't up to doing that. The stability problem should be solveable today, but the fundamental inefficiency problem of pure-thrust VTOL craft remains.
There was lots of enthusiasm for vertical takeoff craft in the 1950s, and quite a few flyable prototypes, some very wierd, were built. Many of them ended up in the Hiller Aviation Museum [hiller.org].
Other than helicopters, the only VTOLs made in any quantity were the Harrier [usmc.mil] and the Osprey [navy.mil], both of which are used by the USMC. Both operate as pure-thrust aircraft only for takeoff and landing; they're ordinary winged aircraft in cruise.
Re:Newton outlawed this type of thing (Score:2)
has nothing to do with this (Score:4)
This is the principle that is used in a rail gun.
I would think that this would be a little like trying pick yourself up off of the ground by your own hair. The forces involved will cancel themselves out. Maybe their is some physics involved that the article did not describe.
Couple Points (Score:4)
2. This is how most scientific 'advances' are made. Somebody notices something cool about the world around them and builds on it.
3. Seems like a reasonable idea (from a 2nd year physics major) but then again I'm no expert on super-conductors or magnetic fields.
4. Everyone agrees that a new propulsion form(s) is needed for space exploration to become a viable and regular occurrence.
5. This is my first post on slashdot so...just take it for what you will.
Comment removed (Score:4)
Re:UFOLOGY (Score:2)
It's not confusion at all. Saying that if we know that it's an alien spacecraft it's no longer unidentified, is akin to saying that if we know that it's a UFO then it's not Unidentified, because we have identified it as a UFO. It's circular logic at best. I say that unknown spacecraft would fall under the category UFO because, how do we define "which" aliens made it. An airplane of unknown origin on your radar screen would be an "Unidentified airplane" right? You know it's an airplane, but not who's airplane ?, so it's unidentified.
LK
What's actually happening here. (Score:2)
Nothing magical, and this _does_ require reaction mass - the conducting object.
Among other things, this is how coilguns work (not railguns; different animal).
Re:Hmm... (Score:2)
Not sure if it's relevant, but does anyone have links to the (theoretical) behaviours of magnetic monopoles? Are there any quirks of nature we would expect to see if these beasties came up?
Sorry, no links, but you might want to grab a hold of a graduate quantum mechanics, quantum field theory, or electromagnetism text book. Magnetic monopoles come in many shapes and sizes, and are predicted in many extensions to the standard model of particle physics. Perhaps the neatest property is that if there is EVEN ONE magnetic monopole, we have an explanation of why electric charges are quantized (see t'Hooft-Polyakov or Dirac magnetic monopoles).
They would have to be extremely heavy objects, though, or else we would already have seen them and their effects.
Why this can work: Re: Newton and Conservation (Score:2)
Well, something does leave this engine. Electromagnetic radiation (you are turning on and off a magnet yes?). Recall duality of matter to mind for a moment and remember that waves are particles as well and have mass. So Newton's 3rd law can be satisfied.
As for Conservation of Energy, you are using energy to run the magnets (and leaking off this radiation) that does not come from nowhere. It comes from batteries and the like which are going to run down because of the EM radiation you project into space. Now you may have solar panels, etc, but we are back in the realm of conventional energy ideas.
So maybe this can work without breaking laws of physics. You just have to think a little bigger. Am I an expert? No. But I've seen thought experiments that suggest you might be able to do this, and they have been reasonably compelling.
Newton outlawed this type of thing (Score:4)
For those of you who are trying to remember exactly what law of physics this violates, it's Newton's Third Law of Motion, For every force there is an equal and opposite force. This means if you don't have something to push off from, you can't go anywhere. (Just for those few of us from the slow class: You can push out a stream of high pressure rocket fuel byproducts, which is how these things usually work.)
I don't see how an asymmetric magnetic field and superconductors help you out--where's the opposite and equal force supposed to come from? It's hard to see how the thing COULD do anything but 'sit there and vibrate'.
Re:Mass change drive (Score:2)
The thing is, the spacecraft gains more forward momentum in step 2 than it looses in step 4....In both cases, I keep wanting to find that missing bit of reverse momentum that leaves the spacecraft vibrating uselessly in place, but I just don't see it!
You're not seeing it, because you aren't looking in the right place :-) If you decide that you are going to rely on a relativistic effect in step 1, then you need to apply a properly relativistically covariant approach to the whole problem. Since energy-momentum is conserved in special relativity, you will find when you carry out the correct analysis, you will be right back where you started: no gain in net momentum for the space-craft if there is no reaction mass expelled.
Think about these questions, and you should be able to find the flaws in your logic: where does the energy come from to heat the mass? When you extract that energy, what happens to the body you extracted it from? What happens to the spacecraft overall if you "radiate the heat away into space" (or, what is heat?).
There's no free lunch; you can't get something for nothing; and you still haven't shown how to violate the second law of thermodynamics or the relativistic versions of Newton's Laws.
Re:It won't work. Physics says so. (Score:2)
Apparently the coupling constant decreases below 1 at high enough energies so that perturbation theory sort of starts to work.
Indeed...the "scale" of QCD (where it becomes strong) is about 1GeV, give or take a few factors of order 1 (right around the mass of the proton and neutron, but I digress...)...perturbative QCD starts to work somewhere above that scale, but really can't be trusted for a while...say 30-40 GeV. By the time you get to LEP energies (200GeV, give or take), the coupling (actually, alpha_strong = g^2/4 PI) is down to about 0.12, and perturbation theory works well.
The professor also said that the coupling constants converge to some common value at about 1e15 GeV.
They do, more or less (but not exactly in the Standard Model). This curious coincidence is one of the best hints for Grand Unification of the three forces.
The fact that they don't meet exactly in the Standard Model is considered (by some!) evidence for Supersymmetry, since in the Minimal Supersymmetric extension of the Standard Model (called the MSSM), the couplings actually DO meet exactly (well, at lest within the current measurement error bars) at somewhere around 10^16 GeV (more or less).
Good luck in the class by the way!
Re:Mass change drive (Score:2)
f you are saying the object becomes more massive when heated due to thermal motions, you are in principle correct. in practice the increased mass is equal to the amount of energy you have used heating it, so it is very very tiny.
Absolutely. I would hate to imagine a substance that could actually be heated enough to make the thing produce useful momentum. It's more of a thought experiment to show that there are possabilities for a reactionless drive that don't involve any magical new laws of physics.
As far as reaction drives, fast neutrons look messy but have some attraction as well. Alpha particles from an accelerater (with an electron beam to maintain a neutral charge) would be more complex but less messy.
I agree that ground to orbit is the greatest problem at this point. That phase carries the greatest risk of total mission loss, and has the most constraints on the mode of propulsion.
space also MIGHT contain (Score:2)
Which would be REAL handy if you found a way to push off on that.
Re:Orbital Mechanics anyone??? (Score:2)
This is a common misconception, but gravity goes out to infinity.
Getting out of the atmosphere and into orbit is definatly the hardest part. The problem stems from the need to get out of the atmosphere and up to orbital velocity in short order. Once that is done, fractional G acceleration over a period of years is acceptable if necessary.
That option opens all sorts of possabilities for propulsion such as solar sails, magnetic propulsion (at least within Earth's magnetic field) , ion propulsion (like Deep Space 1), and probably others.
Ion propulsion engines are very efficient because they have a high ve reletive to chemical engines and can gather the energy needed to accelerate from solar panels. Solar panels provide a much greater total energy over their lifetime than the same mass in chemical fuel. Of course, since the acceleration is limited to fractions of G, it is useless until you get into a geo-transfer orbit.
Risk factors play a role as well. Once in orbit, partial failure of propulsion means the mission takes longer. With good contengency planning this is perfectly acceptable for an unmanned mission. In the ground to orbit phase, the same partial failure means loss of the mission and the potential for substantial property damage and loss of life unless the propulsion is substantially overdesigned (which costs a lot of money as well).
The requirement of multiple G acceleration for ground to orbit limits us to chemical and nuclear rockets at the moment. Skyhook still requires getting out of the atmosphere first. The only other idea right now is a mass driver.
So, even though the delta-v is still just delta-v, it IS a lot harder and more expensive to get from ground to orbit than form orbit to anywhere else.
Things to consider... (Score:2)
Judder judder judder (Score:2)
I want to read about research into really cool drive technology not spaceships (Ion drives, Magnetic Superconductors etc) with the acceleration of an Eastern European car going up a steep hill. I agree we have to start somewhere but more obscure areas of research such as the anti-gravitic properties of superconducting ceramics spinning at high velocity are ignored or worse debunked before they even get off the ground.
"No pseudo literary quotes here"
Definately no millenium falcon yet (Score:2)
Gyroscopic Propulsion systems (Score:3)
an open source gyroscopic inertial thruster [open.org]
a list of space drive patents [spacedrives.org]
someone with way too much time on his hands [physical-congress.spb.ru]
100 anti grav links [mysteries-megasite.com] Take a look at some of those links (with a grain of salt). I would be willing to bet this guy had some sort of setup that upon 'falling' forced the unit mass against the gyroscopic forces of the motor and thats why his result was it 'flying'. I am not a scientist so excuse my ignorance on the mechanics/physics of this subject. It is fascinating...
Magnetic/gravity waves (Score:2)
String theory, for example, considers that the vibrational patterns of a graviton/photon work in such a way as to cancel out measurable mass. But this is only true in a macro-scopic scale.. At quatum sizes (plank-lengths) you'd see an undulating massive string as heavy as a grain of salt shifting around too quickly to have a high net mass effect.
Gyron theory suggests that space isn't empty at all, and in fact is filled with little spinning "gyrons". Mass is the cohesive and circular movement of these gyrons. Transmitter 'forces' are the wripples in gyrons much like watter wripples which spread out throughout infinity (or until ubstructed where their inertia is finally transmitted). Support for such theory is based around disproving that trasmitter forces have "transverse waves". A key point by such theorists is that the only reason we detect individual photons is because our measuring instruments are flawed and various resonant points are allowing the detectors to measure threshold breaches randomly such that we don't maintain a continuously visible ray of light.
String theory adheres to General Relativity AND quantum physics; touting itself to be the Theory of Everything. Gyron theory (and friends) says that Relativistic warping of space is hog-wash - that mass and time manipulation can be totally explained by aerodynamic "Mach" theory, where you treat the gyrons as air molecules.
Quantum theory itself suggests that in any given micro-scopic region of space, you have particle-antiparticle pairs creating and distroying themselves so long as to be within the margin of error that Heisenburg predicted (making use of discrete plank energy levels). So the smaller you look, the more stuff is there; and the more violent that stuff is.
I'm sure there are other anti-vacume theories. Personally I see growing trends between String and Gryon theory, (especially with String's M-Theory which speaks of multi-dimentional undulating strings which sound remarkably similar to Gyrons).
With that background. I make the point that movement through space is exactly the same as movement on the surface of a planet.. We use Friction. It's a highly efficient form of action-reaction.. Arguably, it takes less fuel to drive around the world then it does to blast off into space (where-after you'd get trips around the world for free). Additionally, the slower we travel, the more efficient it is.. This is because the same forces of friction that we use for travel also impeed us (incidently, this is the argument made by Gyrists as to why we can't breech the speed of light or why time seems to slow down for us). On Earth, solid friction is greater than air-friction, so we're good to go. In space, however, the cosmic-dust (beit undulating transmitter forces, spontaneously generated partical/anti-particle pairs, or locally dispensed plasma) is both our means of propulsion and resistance. Well, this relates almost identicailly with swimming in the ocean.. Namely that you have to move like a fish.
In fact, I think that within 100 years, we'll develop cosmic-dust sensative machines that allow us to build space-ships just like fish. Most likely, these won't be big clumsy metalic flippers extended in our rear, but more likely gigantic electro-magnetic jelly-fish-like nets. And when you're within a solar system, such as ours, you have to resort to various sea-fearing tactics to move around... Perhaps it's as simple as inverting the polarity of a magnetic web, or sending out graviton waves, etc.
The point is that I believe Friction-based engines are far more efficient, and better suited to space travel.. If we compare these two types of propulsion (the other being explusion action-reaction drives such as rockets/jets), we see that on earth, Rockets are arguably faster though they do have a max velocity, no matter how much force is applied. Friction based propellants, however, can theoretically approach the speed of light, so long as you can conceive of the proper mechanisms. Rocket fuel, for example propells atoms at around 20,000mph (from what I remember). You can't propell a ship any faster no matter what volume of rocket fuel you use (though larger volumes accelerate you to that speed faster). Ion-drives, likewise _can_ get you near to the speed of light, but you'll run out of fuel LONG before you ever get there.. Plus you need incredible amounts of propellent volume to achieve enough thrust to be useful; thereby reducing your payload and ultimate speed-limit accordingly.
But with mechanical friction, small amounts of energy (of virtually any form) can accelerate a spinning object (or an object on a rail) to unimaginable velocities.. Our current limitations are frictional heat. Most likely we'd have to discover how to manipulate massless transmitter forces so as to not to have 'unwanted' friction (friction in any direction other than that against the target).
Theoretically, this assymetric magnetic pulse device could be used to send out photon-waves (the transmitter force for electro-magnetism) which amplifies the interaction between charged particles (in our case, it would be the plasma from the sun). Now normally, what you'd do is create a massive electromagnet and hopefully repell/attract yourself from/to the sun. (Note: I'm not informed well enough of plasma to know if it tends to have a net positive or negative charge or both) Howver, frequency carries with it energy. And higher frequency photons should produce a higher impact force on charged particles (which should reciprocate.. which is the theorized method by which two similarly charged particles emit symmetric forces on each other). Additionally, it might be possible to funnel the magnetic waves (e.g. photons), say towards the SUN, or a planet (which has a magnetosphere). This would essentially have the effect of a limited tractor/repulsor beam.
Now, from what I gather about String theory, high temperature and pressure cause the various forces (and associated transmitters) to unify. We currently consider electro-magnetism to be unified, and we've discovered electro-weak properties at sufficiently high temperatures. My guess is that magnetism can distinguish itself at sufficiently low temperatures. Here, I totally speculate, however. Low-temperature super-conductors asymetriclly undulating might have something to do with this dispersal of magnetic and electric charge. We've closed down the science of Eletric waves, but might these magnetic waves have their own uses?
Additionally, since we know how to produce electric-waves, possibly now magnetic waves, it might be possible to produce gravitational waves. One reader suggested the use of high-speed, counter-rotating fly-wheels which would increase relative mass. Though he was shot down because of conservation of momentum, which we might be able to gain from this, however, is that if the reletavistic mass changes are fast enough, we could produce gravity waves. We might be able to achieve greater apparent gravitation to a body such as a planet or star through the use of such undulations.. Undoubtedly energy IS being transfered into the system... Where is it going? Obviously into frictional heat.. And to the general entropy of the system. But we also know that electro-magnetic waves will radiate outwards; why not gravitational waves (through the acceleration). Given that acceleration might contain the link to gravity waves (due to changing of reletivistic mass which acts as a doppler effect on observers due to the probagation delay of the gravity information), a counter-rotating fly-wheel might not be the bets model. I simple piston might be the best example.. Here, we can make use of a mechanical energy (such as a gas-engine or rail-gun), where there is massive acceleration of a mass, only to have the inertial spread out in lateral directions. Compression-based energy transfer is very efficient (at least compared to rocket engines). If massive pistons can be rapidly accelerated and decelerated, back and forth, it's possible that gravitational waves would be transmitted. What would be needed are materials with tensal strength beyond imagine (but we're still working towards that). Additionally, as with the above, it might be possible to make full use of massless transmitter forces some day.
In short, I concur with several other posters that there can be no reaction-less net force. I personally believe that Space is not a vacume (especially not around a star), and that those particles can be treated as air or water molecules for propulsion. Depending on the power-requirements of such devices, it might be possible to use Solar cells for propulsions around a star, which gives you enough momentum to direct you towards another star. If Fusion ever becomes practical, then when a stellar-ship passes around a star, it could collect light and heavy elements for use in matter-energy conversion (which is what happens in both fission and fusion), so as to maintain power until reaching the next solar system. I don't think it will be very possible to change course in-between end-points, unless we discover unimaginable power-storage capabilities (perhaps such matter dessimation.. Since we can't vary well conjure up anti-matter sufficiently to sustain matter/anti-matter condensation)
References:
"The elegant Universe" by Brian Greene
But... (Score:2)
Magnetic/gravity waves: Links (Score:2)
gyrons [pitt.edu]
vacum-less aether [aethro-kinematics.com]
Re:Hard to believe (Score:2)
I think there's one obvious useful application, though it might not be quite what you're looking for.
Conservation of momentum (Score:2)
Basically, they suggest that by rapidly applying and removing a magnetic field on a superconductor, they may be able to violate the law of conservation of momentum. My guess is that this isn't going to happen (for values of 'guess' approaching 'absolutely certain')
Re:UFOLOGY (Score:2)
Imagine standing on a kickboard in the middle of a swimming pool trying to propell yourself with the action caused by swinging a bowling ball. I don't see how you'd get anywhere with THIS particular scheme.
Actually, due to friction with the water, you could do it by quickly extending the bowling ball and slowly bringing it back. Of course, that won't work in space.
Re:sig mistake: OT (Score:2)
HTH. HAND.
It won't work. Physics says so. (Score:4)
Re:There is already a "reactionless" drive (Score:2)
Re:It won't work. Physics says so. (Score:2)
Re: The Conservation of Energy (Score:2)
The ship was driven out of the solar system by an array of lasers orbiting Mercury, and braked as it approached its destination star by jettisoning(sp?) part of its mirror and using it for reaction mass. It was a decidedly one-way trip, but damn near possible with today's technology.
UFOLOGY (Score:3)
My first problem with this is if every action has an equal and opposite reaction then how does the movement of the superconducting magnets cause any real change? Sure, their inertia will have an effect, but as soon as they move back into their original position their inertia will cause the opposite reaction.
Imagine standing on a kickboard in the middle of a swimming pool trying to propell yourself with the action caused by swinging a bowling ball. I don't see how you'd get anywhere with THIS particular scheme.
LK
This is stupid. (Score:3)
In this metaphor, to cut the string, you'd have to actually have an infinitely long string, which equates to never shutting off the solonoid, which means you get one 'jolts' worth of accelleration, for as long as you keep the charge in the solonoid.
For the picky, rotating the solonoid 180 degrees while charged wouldn't work either, as it would have exactly the same effect on accelleration as shutting it down and charging it up again with a reversed polarity, so charging, turning, discharging, turning, etc wouldn't work at all. It's like a gyroscope in that capacity.
Kevin Fox
Re:has nothing to do with this (Score:3)
Re:Newton outlawed this type of thing (Score:2)
Shouldn't that be "there's no such thing as a free launch"?
The Simpsons were right again! (Score:3)
- Homer Simpson, underappreciated propulsion physicist
---
Maybe (Score:4)
Goodwin says the metal objects create the judder effect by inducing a "brief asymmetry in the magnetic field" as it is set up when the magnet is turned on. This initial disturbance of the magnetic field, he says, creates a repulsive force on the magnet and pushes it away.
So it's not quite the same thing as a railgun (especially because they claim the magnet is repelled from, rather than attracted to, the metal).
Unfortunately, you might still be right that it's like trying to pull yourself up by your hair. As Mills says at the end, "It's a definite possibility that any forces arising from Goodwin's concept will only act within the components of the device itself, resulting in no net force. There are a lot of unresolved physics issues to address."
So, it is possible, but they just don't know yet.
Re: What law of Conservation of Energy (Score:2)
Wait a minute, this doesn't seem reactionless! (Score:2)
Am I missing some important point here?
Re:Mass change drive (Score:2)
Think about these questions, and you should be able to find the flaws in your logic: where does the energy come from to heat the mass? When you extract that energy, what happens to the body you extracted it from? What happens to the spacecraft overall if you "radiate the heat away into space" (or, what is heat?).
There's no free lunch; you can't get something for nothing; and you still haven't shown how to violate the second law of thermodynamics or the relativistic versions of Newton's Laws.
I think you misunderstand my understanding. I fully expect that the system would require at least as much energy input as it produced momentum (actually more, nothing is 100%).
As for radiating the heat away, it's just to simplify the example (though it will get awfully hot in there is none is radiated). The energy comes from the Ronco Mr. Fusion, a really big spring, or more seriously, a nuclear reactor. It doesn't matter what because I do not expect to get energy for nothing. Some mass will be lost in that process.
So, consider the case again but assume that the ship is perfectly insulated so that it's skin is exactly the temperature of the surrounding space.
Re:has nothing to do with this (Score:2)
So heck, I could be wrong. *grins*
Re:Couple Points (Score:2)
I agree. It's actually quite simple to see how this would work. The judder effect occurs when you place a metal object inside a supercooled magnetic cylinder. So all you need to do is:
See? Easy!
Rocket equation (Score:3)
I begin with the classical (ie. non-relativistic) rocket equation (I use the classical version because relativistic effects only become important for exhaust velocities greater than about 95% the speed
of light, which is not the case for the powers and speeds we are talking about here).
The rocket equation is:
dv = u ln [ ( M + m ) / M ]
where:
dv = change in ship velocity
u = exhaust velocity
M = ship mass, without including reaction mass
m = reaction mass ejected from ship
Now in general, to get from one place to another a ship must accelerate for some time T
The total change in velocity is v, but since the ship speeds up and slows back down to rest, the maximum velocity is v
Now the power required to eject the reaction mass at the given exhaust velocity is equal to the rate of change of kinetic energy of the reaction mass, which is half the mass-loss rate dm
And that's that!
Hmm... (Score:2)
Need... more... detail...
Not sure if it's relevant, but does anyone have links to the (theoretical) behaviours of magnetic monopoles? Are there any quirks of nature we would expect to see if these beasties came up?
Re:Newton outlawed this type of thing (Score:4)
Re:There is already a "reactionless" drive (Score:2)
Plus, there's no concept of a "keel" with a solar sail, so there's no "tacking" and you can really only go downwind. Not overly useful, unless you want to pick up some speed on the way out of the solar system.
Like I told the guy... (Score:2)
...in my dorm back in school who was in shock after his girlfriend had broken into his room and cleaned it. He was taking it pretty hard: "She cleaned my room..." "I can't believe she did that..." "I can't find anything..."
"Mike," I said. "Remember: for every action, there is an equal and opposite reaction..."
Anyway. The idea of using a railgun as an engine is that you'd use it to fire slugs backward, while the reactive force accelerates you forward. As you said, that's just the standard rocket principle, with the slugs as your reaction mass. You're probably right that it wouldn't be particularly efficient compared to a chemical rocket, but it does have the interesting feature of being a way to turn electricity into propulsion, which might be nice if you have cheap electricity. Possibly solar (like the ion drive, which as I recall does basically the same thing with a particle accelerator) or nuclear (how would this compare to just using the plasma directly?)
It might also let you fine-tune the mass/speed tradeoff more optimally -- with rockets, not only do you have to carry the fuel / reaction mass that you'll be using at each part of the trip for all the preceding distance, but most of the energy that you use goes to accelerate the reaction mass backwards instead of you forwards, right? The same force acting over a larger distance means more work done on the reaction mass. That's why a gun's recoil against your shoulder hurts less than getting shot.
This article seems to be talking about either using a magnet to push against a larger magnetic field, which makes sense, but isn't particularly new, or else some new phenomenon that actually breaks the equal-and-opposite-reaction law, which sounds far-fetched, though I've never claimed to be a physicist (I just play one on Slashdot).
David Gould
Re: What law of Conservation of Energy (Score:4)
Re:Newton outlawed this type of thing (Score:2)
It's possible that waving your hands and pointing frantically to Newton's 3rd law is limiting your thinking, just like living in the rennaisance limited him... Maybe challenging old precepts that make use of grand generalization (read: "every force") will get you somewhere.
Certainly blind and unquestioning devotion to Newton is contrary to the healthy skepticism that fuels science. But extraordinary claims demand extraordinary evidence. The article presented no evidence, no explanation, at all.
Re:Newton laws (Score:2)
Magnetism does not contravene Newton's laws of motion.
Re:Couple Points (Score:2)
The first 200 miles are the expensive bit. You have to carry the fuel to fight the gravity. and the fuel to carry the fuel that fights the gravity. And so on until you end up with massive booster rockets, etc.
Once you're in orbit, getting other places is a lot cheaper. If we have cheap orbital shots, we'd have had a decent space station decades ago and probably explored other planets by now.
_____
Re:Newton outlawed this type of thing (Score:2)
Maybe from the magnetic field around? It's like the space tethers work: if you pump electricity into them they'll push you up by reacting with planet's magnetic field.
Actually, this isn't "reactionless"--as you use the earth's magnetic field to push off, you push the planet in the opposite direction. (After all, it's pushing against YOUR magetic field.) This obviously has its uses, but has limits as well--if there's no planet with a strong magnetic field in the vicinity, and if it's not oriented the way you need, you're not going anywhere.
I also don't think that's what the article is talking about-- after all, your idea of a space tether works fine without having to resort to any mumbo-jumbo about 'judder'. A true reactionless drive would indeed be a breakthrough, but as I mentioned in another response, extraordinary claims demand extraordinary evidence.
Re:Couple Points (Score:2)
Good overview of reaction drives (Score:3)
Just got pointed here this morning, which has a good overview of reaction drive technology now and in the future. Seemed sort of relevant.
http://astp.msfc.nasa.gov/4thgen_main.html [nasa.gov]See the link 'Really Advanced Propulsion Research' down side bar.
A good vibrator, a bad space ship. (Score:3)
Magnet josts one direction, spaceship jolts the other.
Spaceship retracts magnet to repeat process, spaceship is retracted towards magnet EXACTLY as much as initial jolt.
This is a GOOD way to make a vibrator, but a bad way to make a space ship.
Re:It won't work. Physics says so. (Score:2)
Physics does indeed say it won't work. The universe, however, has a habit of disregarding how we think it should work.
$ man reality
Re:Newton outlawed this type of thing (Score:2)
Then again, it may not.
EJB
another magnetic reactionless drive (Score:2)
I remember reading about someone elses idea for an electromagnetic thruster here [easynet.co.uk]
I have *no* idea if this is physically possible (or even if the website is serious :)
Re:The law of Conservation of Energy (Score:5)
Pedantry aside, the only effect I could think of that might cause this, outside of an external field (due to sun, earth etc) would be the time delay between one end of the coil carrying a current and the other end carrying a current due to light travel time difference effects between the superconductor and the free space inside the coil. One end of the coil would be magnetised to a fairly high field and and the other would not, for the time it takes the current to build up in the coil. This time would be at tleast the time it takes for an EM wave to propagate down the coil (including going around all the loops). In the meantime a large magnetic field would build up in the space inside coil, with the speed of build up of the field limited only by the light travel time from one end of the coil to the other, and be expelled by the build up of eddy currents in the superconductor coil, before the driving current got there.
As for the law of conservation of momentum, the above effect, could possibly cause a large EM pulse to be emitted, which would have a momentum in one direction, and so there would be an impulse in the other direction. I don't know if the same effect would be observed on suddenly switching off the current, as I think the impulse produced _may_ depend on the switching speed, and if the magnet isn't switched off as quickly as it is switched on, a net momentum may develop. If this isn't the case, the magnet will just sit there and vibrate.
This is all just thinking straight into the comment, so I've got quite a high chance of being wrong. (more so than usual)
Re:Newton outlawed this type of thing (Score:5)
Re:Judder judder judder (Score:2)