Challenging Physics Question (Mass moment of inertia, pendulum)

1. Dec 1, 2005

patrat

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):
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?

2. Dec 1, 2005

mezarashi

Does it have to be by this means? If yes, I think it may be related to the 'breaking physics' part you mentioned later.

3. Dec 1, 2005

patrat

I have to solve the problem using the equations for pendular motion. I checked all my formulas with textbooks and the internet, and all my equations and values seem to line up...