If the point charge moves fast enough, another factor comes into play.
To see how this scenario works, consider the case in which just a point charge moves across the surface of an insulator.
The photoemitted electron (el) is modeled as a negative point charge that moves along the z-axis [ρ = 0, zel(t)].
The point charge is initially moving radially toward the large sphere at 9 radii (of the large sphere), with enough energy to reach 1.5 radii (only 0.5 radii above its surface), at which point it reverses direction.
In that case, the polarization pattern moves with it, becoming so-called evanescent waves that still attract the point charge.
However, if the point charge is replaced with a rodlike line of charges that moves sideways like a knife spreading peanut butter then the force from the surface can become repulsive, Rebernik Ribič argues.
If the magnet is thought of as a current loop, then on one side of the loop the electric field from the point charge pushes the electrons in the direction in which they're already moving and boosts their energy.
Now, if a point charge above the insulator whizzes along faster than light can within the material, then the induced polarization pattern will move that fast as well and create Cherenkov radiation.
At which point charging technology will likely have moved on again.
