Physicists Turn Pull Into Push

sciencehabit writes "It's textbook physics: An electric charge near the surface of a material gets pulled toward the surface. However, if the charge is spread out into the right shape and moves fast enough, that attraction becomes a repulsion, one physicist calculates. The odd finding could help physicists avoid unexpected effects when guiding beams of particles such as electrons."

Re:ION engines?

[Anonymous Coward]

It isn't like an ion engine at all. What they are saying is that electrostatic induction [wikipedia.org] is not always attractive but it takes very specific conditions to make it repulsive. An ion engine doesn't use induction. Induction is the force between a neutrally charged object and a charged object.

Re:theoretical bs

[Chuckstar]

Nothing in the article violates the laws of physics. It's merely a question of who did the math more accurately for the specific case of the given arrangement of electrons.

Cherenkov radiation is a well understood phenomenon. What you are missing is that the cosmic speed limit is the speed of light in a vacuum. Where the speed of light is slower (i.e. glass), it does not violate the laws of physics for a particle to move faster than that speed. In the given example: the electrons move faster in glass than light moves in glass, but still slower than light moves in a vacuum.

Re:theoretical bs

[History's Coming To]

Nope, they're referring to Cerenkov radiation [wikipedia.org], it's a known effect and produces a very pretty blue light in nuclear reactors. It occurs when the phase velocity travels faster than the speed of light in that medium which is all fine and dandy and breaks no rules at all.