# Can a charged particle be in uniform motion in reality?

1. Jul 11, 2014

### Subhra

If a charged particle is at rest, external magnetic field cannot move it. If an external electric field is applied, the particle will get accelerated. Now the external magnetic field will exert a force on the particle perpendicular to its motion. This will change the direction of motion of the particle.

However, in magnetostatics, there is a frequent use of uniform motion of charge particle.

Is this "uniform motion" just a hypothetical postulate to formulate the theories or such a motion can really be created?

If a charged particle can really move in uniform linear motion it seems very interesting to know about the forces acting on the particle and how the forces are balanced.

2. Jul 11, 2014

### HallsofIvy

Staff Emeritus
In your example, you have a charged particle "at rest" and then start it moving. Since that requires an acceleration, obviously it cannot be in "uniform motion". But a charged particle that is already moving in open space with no electric or magnetic field will be in uniform motion.

3. Jul 11, 2014

### Subhra

Dear Hallsoflvy, I think, I didn't explain the problem properly. If a charge be initially at rest or in acceleration, can it's velocity be changed so that it starts moving with uniform velocity?

4. Jul 11, 2014

### Staff: Mentor

How can it start moving with uniform (non-zero) velocity if it's at rest? You can arrange for it to accelerate briefly, then have uniform velocity.

What do you mean by "or in acceleration"? If it's accelerating, and you stop the acceleration (by removing the fields), then it will continue with uniform velocity.

5. Jul 11, 2014

### Subhra

Yes, Doc Al I agree with you. To make a charge move with uniform velocity, it first needs to be accelerated in electric field and then the field needs to be dropped.

6. Jul 11, 2014

### ModusPwnd

Or you, the observer, needs to be accelerated briefly. :tongue: