Magnetic Orbit?

[Czman007]

I was just wondering if it is possible to create and maintain an orbit using magnets. For example, could a satellite hold a smaller satellite in orbit around itself use magnets? Do magnets work that way?

[LukeTim]

I was just wondering if it is possible to create and maintain an orbit using magnets. For example, could a satellite hold a smaller satellite in orbit around itself use magnets? Do magnets work that way?

Well, if the magnet is strong enough then I can't imagine why not... provided you could ensure somehow that the force is always attractive, so it is then an effective allegory for gravity, you wouldn't want one magnet spinning around and starting to repel the other away.

I guess monopoles could achieve this, though I don't know whether they exist at a macro scale.

[SunJumper]

Yes, in fact, this is the basis behind mass spectrometers....

[ramipro]

This reminded me of a video I saw a couple months ago on youtube. I get you the link. It is about electromagnetism on the ISS, which make droplets of water orbit around a knitting needle charged with stating electricity, and since electricity and magnetism derive from the same force, i guess it also applies

[Sillychris]

If you launch an electron in a uniform magnetic field and its velocity is perfectly perpendicular to that field:

It will go in a circle. Forever.

[FanaticalFighter]

ramipro: That video was amazing! Thanks for posting it here.

[K^2]

That's actually a complicated question, and that knitting needle video is a big part of the answer.

You can't have magnets orbiting each other the same way you do with planets. The reason is that there is no such thing as magnetic monopoles. All magnets have magnetic dipole, but no net magnetic charge. And dipoles, instead of the normal inverse square law follow the inverse cube law. And to have stable orbits, you do need inverse square law.

But that's where that knitting needle video comes in. The electrostatic attraction there is also a dipole attraction. There is some net charge on the needle, but not on the droplet. However, the small net charge of the needle polarizes the droplet, and droplet starts to work like an electrostatic equivalent of a magnet. No net charge, but lots of dipoles. So why does it stay in orbit around the needle? The trick here is that it is a needle, and not a sphere. The fact that it's a long cylinder makes it work like a 2D problem. Only distance from nearest point on the needle matters. And in 2D, dipoles follow an inverse square law. So the droplet orbits the needle in the plane perpendicular to the needle, but mostly free to bounce around along the length of the needle. (There are some interesting edge effects that prevent it from "sliding off" the needle during all of this.

So can this work with magnets? In principle, yes. You need one magnet that is long and cylindrical. But it's not just a bar magnet. Its North and South poles shouldn't be on opposite ends, but rather on opposite faces of the cylinder. This is important for stability. Now, you should be able to send a small magnet orbiting around it. I'd take a little puck-shaped magnet, and give it a bit of a spin to gyro-stabilize it, so that it's north and south poles are always aligned to attract to the cylinder magnet. Give the small magnet a bit of a push, and it should stay in a circular or elliptic orbit around the long one.

[Idobox]

as SunJumper and SillyChris said, an electric charge in a uniform magnetic field will go in circles.

What they didn't say is that the particle will loose energy through synchrotron radiation (EM waves) and will stop moving after some time.

You can use complex tricks to achieve the same thing with only magnets, but you will still loose energy to radiation (moving charges or magnetic fields cause EM radiation).

By the way, planets emit gravitational waves as they orbit, but those are so weak, their effect is not measurable.

[LordOfTheOrbits]

This is possible and used in particle colliders to keep the particles inside the beamlines.

[Sillychris]

the particle will loose energy through synchrotron radiation

They didn't tell me that in phys 381 and now I'm mad at the U of A.

KSP just contributed to my education... again.

[Idobox]

Think of it, you have charge moving, which means it creates a varying electrical field, which means EM waves.

Every time you deflect a charged particle, you create EM radiations, with different names depending on how you do it (Bremsstrahlung, synchrotron, even Cerenkov I think)

[K^2]

Idobox, just being pedantic, perhaps, but moving charges don't radiate, because you can always go into coordinate frame where they are static.

It's the accelerating charges that radiate. Of course, motion in any closed orbit requires acceleration, so motion in orbit always results in radiation. And yes, you are absolutely correct that this will also happen for accelerating magnetic dipoles and accelerating mass.

[peadar1987]

Just put the central magnet on a gimbal so it can spin. Its south pole and the orbiting magnet's north pole will automagically align. Give the outside magnet a carefully-considered nudge, and it will begin to orbit. Now, the forces are going to dissipate very quickly, so you'll most likely end up with the orbiting magnet stuck to the side of the central magnet, oriented in the opposite direction.

[Idobox]

You're right, important precision.

I was trying to stay simple, but ended up oversimplifying.

[lajoswinkler]

When charge orbits in an electric or magnetic field, it accelerates... its vector component changes. It is not intuitive because we experience acceleration through scalar change.

So every time a charge accelerates, it loses energy carried away by photons.

[henryrasia]

I was wondering if one could replicate this setup on Earth by using a same charge metal plaque on the bottom to keep the droplet floating. Something like this:

Two questions:

1) Would this setup even work?

2) How would the physics of the orbit differ from gravitational orbits? (for example Kepler's laws and equations)

I ask this because Coulomb's Law gives the impression they should be the same, but with a different constant. Any physics I'm missing out on with this train of thought?

[Ralathon]

I was wondering if one could replicate this setup on Earth by using a same charge metal plaque on the bottom to keep the droplet floating. Something like this:

http://i.imgur.com/oYWtsfn.png

Two questions:

1) Would this setup even work?

2) How would the physics of the orbit differ from gravitational orbits? (for example Kepler's laws and equations)

I ask this because Coulomb's Law gives the impression they should be the same, but with a different constant. Any physics I'm missing out on with this train of thought?

First of all, Necro!

Second of all. No, it wouldn't work.

The problem is the levitation bit. The electric field above that plate won't be uniform, it will point slightly away from the center. So unless you have a infinitely large plate the charge will accelerate away from the plate's center. Second of all, the levitation system would be horribly unstable. The electric field of a very large charged plate does not drop with distance (Assuming your test point stays reasonably close to the surface). So there would be no natural feedback mechanism in your rig. If your voltage on the plate is slightly too high your droplet flies off into infinity, slightly to low and it falls.

A second problem is the "Droplet in a vacuum" thing. A droplet in a vacuum very rapidly stops being a droplet.

If you manage to find some other means of levitation and dump the vacuum, sure it'd work. Since you don't need your setup to last long you could heat the plate to a few hundred degrees and abuse the leidenfrost effect. Not as accurate as pure levitation, but good enough for demonstration purposes.

[henryrasia]

The problem is the levitation bit. The electric field above that plate won't be uniform, it will point slightly away from the center. So unless you have a infinitely large plate the charge will accelerate away from the plate's center.

OK, can this effect be accounted for? As in have the plate be a concave disk to compensate this?

Second of all, the levitation system would be horribly unstable. The electric field of a very large charged plate does not drop with distance (Assuming your test point stays reasonably close to the surface). So there would be no natural feedback mechanism in your rig.

I'm not sure I understand what you mean. Why would I need the charge to drop with distance? I want it to be as uniform as possible. Would you care to explain?

[lajoswinkler]

I was wondering if one could replicate this setup on Earth by using a same charge metal plaque on the bottom to keep the droplet floating. Something like this:

http://i.imgur.com/oYWtsfn.png

Two questions:

1) Would this setup even work?

2) How would the physics of the orbit differ from gravitational orbits? (for example Kepler's laws and equations)

I ask this because Coulomb's Law gives the impression they should be the same, but with a different constant. Any physics I'm missing out on with this train of thought?

It's not easy for me to answer because there you have a complex electrical field. It's not easy like in famous Millikan's experiment. However I'm pretty sure that if you used an atomizer with poorly volatile (or not volatile at all, like ionic liquids) liquid, you could get at least some of the droplets to orbit for some time. The key is in lots of droplets introduced into the chamber.

Also, you'd need an optical device to see them, or perhaps a laser light in a form of a plate to make the droplets shining.

Other than that, Coulomb's law is basically of the same construction as gravitational law.

You could have, instead of a positive plate, a positive U-shaped bottle. That should give more stability the system.

[henryrasia]

Would it be better to just use a plastic sphere, like a airsoft pellets? How would one charge a plastic at a specific voltage? I'm thinking plastic because metal would lose its charge very quickly.

And about an U shaped bottle, wouldn't that interfere with the orbit? Because electromagnetic force has infinite range, while a plate on the bottom would only make perpendicular force and therefore not interfere at all. How do you make an uniform charge "bed" perpendicular to gravity?

[lajoswinkler]

You'd need a computer to simulate fields here. My brain is not powerful enough.

You charge the orbiting bodies by bombarding them with x-rays. Just like Millikan did.

[Teamwork]

I don't think electric orbits would work because of Bremsstrahlung radiation. I don't think magnetic ones would work either because you would have to take into account the dipoles of the magnet(s).

[lajoswinkler]

I don't think electric orbits would work because of Bremsstrahlung radiation. I don't think magnetic ones would work either because you would have to take into account the dipoles of the magnet(s).

Hm, what does bremsstrahlung have to do with this?

[peadar1987]

Hm, what does bremsstrahlung have to do with this?

Think he means cyclotron radiation.

Bremsstrahlung is the secondary radiation emitted when primary radiation interacts with matter.

[henryrasia]

I know the particle would continuously discharge, very different from the constant mass of planets. But my question is how can I make a particle orbit around a copper cable with electromagnetism, on Earth, for as long as possible.