# Moment of Inertia Experiment

1. May 15, 2012

### massb

In my experiment based on the inertia the angular velocity or speed goes either up or down with the angular momentum remaining the same. I understand that when a person is rotating to change the inertia you would either extend or detract the arms and legs (think dancer). I understand this concept and even somewhat how the calculate it except my angular momentum.

L=Iw since my inertia is changing how do I find the changing w(angular momentum) if I don't know the value of the L(angular momentum) yet. Would I just physically count the number of rotations per second in radians for each time the inertia is changed?

2. May 16, 2012

### sk9

Hi welcome to phy forum(everyone does that so i did it too for your first post)
Well you dont know the L now but i hope that you know the speed at which the dancer is expanding her/his arms(& her mass and her arms mass....etc). So you will calculate L(t) as a function output of time and you must know both L & w at some instant (maybe before after she moves her arms)simultaneously, this way you will know w(t).

NOOOOOOOO! dont count the number of rotation per second, I have no grudge over counting but it will give an average w over a time of 1 sec, which will be hazardous if w is not constant.

3. May 16, 2012

### tiny-tim

welcome to pf!

himassb! welcome to pf!
angular momentum is difficult to measure directly (if you don't know the moment of inertia)

the only convenient way i can think of is to transfer all the angular momentum to a "reference" body

what exactly is your experimental set-up?​