Page "Phonograph" Paragraph 113

Even on a perfectly flat LP, tonearms are prone to two types of tracking errors that affect the sound.

As the tonearm tracks the groove, the stylus exerts a frictional force tangent to the arc of the groove, and since this force does not intersect the tone arm pivot, a clockwise rotational force ( moment ) occurs and a reaction skating force is exerted on the stylus by the record groove wall away from center of the disc.

Modern arms provide an anti-skate mechanism, using springs, hanging weights, or magnets to produce an offsetting counter-clockwise force at the pivot, making the net lateral force on the groove walls near zero.