Moment of Inertia and the IPS system.

[jasc15]

IPS drives me nuts. If I know an object's weight in lbf (a flat, 10" radius disk for simplicity's sake), and want to find it's MOI, the formula is I = 1/2*w/g*r². Now here's where i get confused:

Since I have the object's weight in lbf, it's mass is numerically equal, so a weight of 2.6lbf on Earth has a mass of 2.6lbm (right?) and the MOI is I = 1/2 * 2.6lbm * 10² = 130lbm*in².

So how do I get around dividing by g? Also, are the units of lbm*in² numerically equivalent to lbf*in*s² (i.e., 130lbm*in² = 130 lbf*in*s²)?

 

[timthereaper]

1 lbf = 32.174 lbm*ft/s^2, which is really just F=mg.