Karl Miller writes:
>The heat from the passing of needle repeatedly can warm up a disc and
>eventually cause changes in the groove.
At the risk of wandering afield of the subject of music: my understanding
is that the passage of the stylus actually deforms the groove, due to
the pressure involved, rather than any heat generated. This plastic
deformation is recoverable (the groove slowly returns to its original
shape) but not if it is further deformed by repeated playing before it
has had time to fully recover.
Even at a gram or two of tracking force, the contact patch is so small
that the pressure (kg/m^2) applied is enormous.