OK, the chuck jaws have a given mass (measured in either kg or lbm) and a specific center of mass (also called center of gravity). If you have these to values, the acceleration they undergo is given as a = v²/r where r is the distance in m or inches from the center of the spindle to the center of mass. v is the rpm of the spindle * r * 2 * pi / 60 and will end up in either m/sec or in/sec. Thus, your acceleration ends up as: a = 4 * pi² * rpm² * r / 3600.
1 lbm X 1 g = 1 lbf. Thus, if you are using lbm and inches, your force per chuck jaw will be: F = ma = (M lbm * 4 * pi² * rpm² * r / 3600) / 386.09 -- where 386.09 is 1 g in inches/sec².
The caveat here is that though a kg is supposed to be a measure of mass, the unit kgf, which is 1 kg X 1 g has become quite common in recent years and, if your measure was in kgf, then the acceleration needs to be divided by 9.807 m/sec² to turn it into a measure of gravities. I work with a number of European-based companies that regularly supply "mass" values in kgf -- and often do not distinguish between mass and force which leads to major confusion (especially as the "proper" measure of force in the metric system is that worthless measure the Newton -- which is why the kgf has come into usage)!