  We present a number of arguments to demonstrate that a quantum analog of
Cherenkov effect occurs when two dispersive objects are in relative motion.
Specifically we show that two semi-infinite plates experience friction beyond a
threshold velocity which, in their center-of-mass frame, is the phase speed of
light within their medium. The loss in mechanical energy is radiated away
through the plates before getting fully absorbed in the form of heat. By
deriving various correlation functions inside and outside the two plates, we
explicitly compute the radiation, and discuss its dependence on the reference
frame.
