Hello, as you can tell by the hour I have been at this problem for quite some time now. I am trying to find the mass moment of inertia (rotational inertia) of a baseball bat; by means of using the equations for pendular motion. Here are the equations: Distance from pendulum pivot to pendulum center of gravity: Lcg=1.144 meter Mass of pendulum: m=0.840 kilogram Time Period of pendulum: T=2.1 seconds Angular speed of pendulum (calculated from period): w=2.99 radian/second gravity: g=9.81 meters/second^2 Mass moment of inertia about pendulum pivot: Io=what the equations solve (kilogram*meter^2) The equation is: Io=(m*g*Lcg)/(w^2) or equivalently Io=((T^2)*m*g*Lcg)/(4*pi^2) for this I get, everytime, Io=1.05 (kilogram*meter^2) The trouble is coming though Icg=mass moment of inertia about pendulum's center of gravity parrallel axis theorem: Io=Icg+m*Lcg^2 which becomes: Icg=Io-m*Lcg^2 which spits out: Icg= -0.045 (kilogram*meter^2) Thats right... a negative number. That violates intuition and the laws of physics for a physical solid. How did I break physics? What did I do wrong and how do I fix it?