The root meansquare of distances from the center of gravity to the edge of a rigid body gives this quantity (*) "ofgyration".
The sixth power of this quantity is proportional to the differential cross section of Rayleighscattering. In Stokes' law, it is multiplied by the settling velocity, dynamic viscosity, and six pi to givedrag. One form of this quantity is the ensemble average of the interparticle distance. The root meansquare of distances from the center of gravity to the edge of a rigid body gives this quantity (*) "ofgyration". The moment of inertia of a collection of particles is equal to the sum of the product of the masstimes the square of this, and the moment of inertia is equal to two-fifths times the mass times this quantitysquared for a solid sphere. For 10 points, name this value, the cube of which times four thirds pi gives asphere's volume.
The sixth power of this quantity is proportional to the differential cross section of Rayleighscattering.
radius [or r or diameter or d; prompt on "size", "distance", "length", or "displacement"]