Blender speed may also be a key to mixing efficiency. At lower blender speeds, the shear forces are low. Though higher blending speeds provide more shear, it can lead to greater dusting resulting in segregation of fines. This means that the fines become air-borne and settle on top of the powder bed once the blender has been stopped. There is also a critical speed which, if approached will diminish blending efficiency considerably. As the revolutions per minute increase, the centrifugal forces at the extreme points of the blender will exceed the gravitation forces required for blending. Consequently the powder shall tend to gravitate to the outer walls of the blender shell. As the size of the blender increases, the rotational speed decreases usually in proportion to the peripheral speed of the blender extreme. V-Blenders are designed to operate at 50% to 80% of the critical speed.