# Retarded field interaction

I was doing the following thought experiment: imagine a particle that moves at a certain velocity. Imagine also that the particle generates a field that propagates at velocity $v_f$. Well, if the particle's velocity is higher than $v_f$ then it will interact with its own field if for some reason the particle decelerates (imagine a plane that goes Mach 2 and then "brakes" to zero, it will hear its own sound after a while). But what if the particles's velocity is exactly $v_f$?

My guess is that it will interact with its own field... is this correct?

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