Due to the offset between the cartridge's axis (which is approximately tangential to the disc) and the tonearm's pivot, the force applied (through friction) by the rotating disc to the cartridge tends to draw the tonearm toward the center of the record and distort the balance of the sound and of the wear suffered by the stylus. To prevent this, a small force is applied at the tonearm. This consists of various contraptions depending on the tonearm's manufacturer, ranging from small counterweight adjustable by a knob to spring or magnetic mechanisms.
Note that while the angular velocity is almost constant, the peripheral velocity is not, varying for instance from approximately 50 cm/s down to 15 cm/s from start to finish of a 33 rpm, 30 cm record. The angle which the tonearm rests on the record is also variable.
- "US Patent 3948529 - Phonograph turntable anti-skating device". Google Patents. Retrieved March 15, 2015.