Trying to understand moment of inertia; example of a rod

1. Feb 23, 2006

teng125

i found smtg that i don't understand.moment of inertia = 1/3 m(r^2) stands for which type pf rod??or reference point??

2. Feb 23, 2006

Staff: Mentor

The moment of inertia of a thin rod of length L about one end is:
$$I_{end} = \frac{1}{3} M L^2$$

About the middle, it would be:
$$I_{cm} = \frac{1}{12} M L^2$$

(Set up the integral $\int r^2 dm$ and see for yourself!)

3. Feb 23, 2006

vaishakh

Don't understand something like that. Do the integration by yourself and derive the result. Anyway it is for the moment of inertia of a uniform rod, suppose AB, with respect to its ends A or B.
There is no complication in the integral. Just think about relating dm with dr.