In an ideal universe there would be no bearing friction. Admittedly, this never happens. But in such a closed system, a force equal in magnitude and opposite in direction, i.e., counter-clockwise in this case, would be exerted on everything that is not part of the platter, when the motor is in action. In the real world, gravity pulls the assembly down on its base, and the friction between the footers and the shelf normally prevents the counter-rotation of the assembly. But the contrary force is present, nonetheless. (This is a problem with spring suspended turntables.) By having the counter-rotating platter of equal composition and mass borne on the same assembly as the functional platter, that force is nullified.
Think about it; in outer space, in a manned space capsule, one could not play a record unless one bolted down the whole turntable to the mass of the ship itself. Otherwise, the platter and the rest of the turntable would both rotate but in opposite directions due to the rotational force put into them by the motor. (Of course, setting VTF would be a bitch as well.)
Think about it; in outer space, in a manned space capsule, one could not play a record unless one bolted down the whole turntable to the mass of the ship itself. Otherwise, the platter and the rest of the turntable would both rotate but in opposite directions due to the rotational force put into them by the motor. (Of course, setting VTF would be a bitch as well.)