According to the article "Cutting LPs, the Theory" published in Studio Sound 1975-07, "The frictional force acting on the stylus point pulls the stylus point in the direction of the groove motion with a force of about 25% of the playing weight (tracking force)".
However, as the following video shows, the drag from the LP groove is continuously variable, which if there is no speed servo, could conceivably cause modulation of the platter RPM according to the instantaneous dynamics and frequency content of the music.
https://www.youtube.com/watch?app=desktop&v=j0ZuukxmaVM
However, as the following video shows, the drag from the LP groove is continuously variable, which if there is no speed servo, could conceivably cause modulation of the platter RPM according to the instantaneous dynamics and frequency content of the music.
https://www.youtube.com/watch?app=desktop&v=j0ZuukxmaVM