Electromagnetic propulsion. (Not?)

[Bob not Alice]

Hi folks,

This is such a simple idea that I know I can't be the first to think of it so there has to be a "gotcha". Maybe an induced electric field working in the opposite sense? Is there a kind soul out there who can spare a few moments to educate me after reading what follows? Thanks

About 40 years ago I asked myself if one could take advantage of the light speed propagation delay and came up with this:

http://andersson-design.s3.amazonaw...n the face of conservation of momentum. Bob.

 

[sophiecentaur]

You could look up 'Linear Motors for Rail Transport " and "Rail gun". All you need to do is to set up a traveling wave of magnetism along a track and your projectile / locomotive will follow it.

 

[Bob not Alice]

.
Thanks for the prompt response: my childhood hero was Eric Laithwaite. But the effect I'm describing and seeking help with is the apparent, and hence rather unlikely, violation of conservation of momentum as all that's needed for the "motor" described above is that the electromagnets are held a fixed distance apart. The whole assembly can be in space, for example. So I'm missing something - either an effect that negates any thrust or a balancing radiation emission.

Bob.

 

[nasu]

How do you keep the electromagnets a fixed distance apart?

 

[Nidum]

Much more interesting :

https://www.google.co.uk/search?q=emdrive+nasa&ie=utf-8&oe=utf-8&gws_rd=cr&ei=z8XAVYzAD8LwUOfygfgB

 

[Bob not Alice]

Hi nasu,

Mechanically

Bob.

 

[Bob not Alice]

Much more interesting :

https://www.google.co.uk/search?q=emdrive+nasa&ie=utf-8&oe=utf-8&gws_rd=cr&ei=z8XAVYzAD8LwUOfygfgB

Yes, that was why I dusted off my old idea. But I'm not sure whether the operating principles involved are quite the same. Maybe they are but I'm really hoping that someone with a deep knowledge of electrodynamics can point out what's wrong with the simple assumptions in my opening post.

Bob.

 

[Gaz]

lol at bob nice simple answer =)

EM is definitely the way to go though just about everything in the universe revolves around it =)



When NASA fired a laser through it the particle's were faster than the speed of light is this true how can a magnetic field propargating at the speed of light propel laser light faster than the speed of light ??

 

[Drakkith]

The idea is that by the time the magnetic field at A with, let's say, the north pole on the left arrives at B the field generated at B has its south pole on the left so B is attracted towards A. But by the time the field generated at that instant from B reaches A the polarity at A has flipped so A is repelled. The frequency of oscillation can be chosen for a given separation of the electromagnets so that, with a 90 degree phase difference, this imbalance never reverses. An observer at B always sees an oscillating field generated by A exactly in step with his own field but with opposite polarity while an observer at A sees an oscillating field from B exactly in step with her own and the with same polarity.

Yes, for any significant strength of interaction the frequencies are horridly high but I've never understood what must be happening to counter the simple minded assumption stated above that B is always attracted by A and A is always repelled by B which clearly flies in the face of conservation of momentum.

I don't know the answer, but I bet you'd have to include things like mutual induction, which would probably act to stop this from happening the way you're thinking it would.

 

[berkeman]

EM Drive is nonsense, and is specifically listed in the PF Rules as a Forbidden Topic. Thread is closed.

Forbidden Topics -- EMDrive and other reactionless drives
Articles suggesting that NASA, the Chinese government, or some other governmental actor is working on such a technology frequently appear in the popular press. These claims have been extensively debunked and are not acceptable references under the Physics Forums rules.