Torque the vector cross product, p is the particle's linear momentum, and r is the displacement vector from the origin (the origin is assumed to be a fixed location anywhere in space). The time-derivative of this is: This result can easily be proven by splitting the vectors into components and applying the product rule. Now using the definition of force formula_17 (whether or not mass is constant) and the definition of velocity formula_18 The cross product of momentum formula_20 with its associated velocity formula_21 is zero because velocity and momentum are parallel, so the second term vanishes. By definition, torque τ
Constant linear velocity CAV systems are used. This is because seek performance would be greatly affected during random access by the requirement to continually modulate the disc's rotation speed to be appropriate for the read head's position. Zoned Constant Linear Velocity (ZCLV) is a modification of CLV for high speed CD and DVD recorders. Early model recorders were CLV drives. The recording speed on such drives was rated in multiples of 150 KiB/s; a 4X drive, for instance, would write steadily at around 600 KiB/s. The transfer rate was kept constant by having the spindle motor in the drive vary in speed and