Question

Rigid body rotation, and angular velocity!

http://www.youtube.com/watch?feature=player_detailpage&v=EOy1NV21pMY#t=1011

so this is a fairly simple problem, Lewin gives a push to the ruler, and we need to calculate the velocity of CM and the angular velocity.. the part i don't understand is he says we can calculate angular velocity by considering the reference point where the push was done.. i just don't get it how to calculate angular velocity WITH RESPECT TO THAT POINT?!.. that doesn't even make sense to me. I am breaking my head over this!!

Answer 1

Here.. i uploaded the work..
part a) is the simple way

part b) (supposed to be more simple).. but i just don't understand the concept of finding angular velocity at some point..

Answer 2

Walter Lewin is wrong in its notation: for a rigid body, there is no such thing as rotation velocity 'at a certain point'. ω is an intrinsic property of the body , so there is only one ω in the problem. It is misleading to write ωcm or ωp.

Answer 3

Solving the problem at point P is not faster than solving it at point G, because in both cases, you need to work out what vcm is.

Answer 4

btw, your answer \(\omega = \Large \frac{Id}{I_c}\) is correct.

Answer 5

"the part i don't understand is he says we can calculate angular velocity by considering the reference point where the push was done.."

my gut is telling me that what is he means is - angular velocity is calculated from a reference point that appears to be stationary, because we are assuming the chalk board to be stationary.