Go Back   Physics Help Forum > College/University Physics Help > Advanced Mechanics

Advanced Mechanics Advanced Mechanics Physics Help Forum

LinkBack Thread Tools Display Modes
Old Sep 1st 2012, 09:54 PM   #1
Join Date: Jul 2012
Posts: 67
The concept of conservation of angular momentum

I always read that conservation of angular momentum is with respect to an origin of our choice, so if we want to compare the angular momentum of two situations, we have to calculate the angular momentum in these situations with respect to the same origin. However - I've seen in some questions that there's conservation of angular momentum, but the calculation of it in each state is with respect to the center of mass. Now comes the twist - between these two states the center of mass itself has changed it's position in space (like with a rod that spins as it's making translation movement as well - in t=0 the rod can be at the left side of a room and in t=t' it can be at the right side of the room, it's clear that the center of mass of the rod is not at the same position in space).

I'd like to know what is the mathmatical justification for this comparison even though the origin between the two states is not at the same location.
assaftolko is offline   Reply With Quote
Old Sep 2nd 2012, 08:26 AM   #2
Physics Team
ChipB's Avatar
Join Date: Jun 2010
Location: Morristown, NJ USA
Posts: 2,290
The justification is that the two components of momentum - linear and angular - are vectors that can be added independently. The angular momentum components is most easily calculated with respect to the instantaneous position of the cm, which as you note may change as the object moves laterally. The first few pages of these notes may help:


Also see the description of angular momentum here: http://en.wikipedia.org/wiki/Rigid_body_dynamics
ChipB is online now   Reply With Quote

  Physics Help Forum > College/University Physics Help > Advanced Mechanics

angular, concept, conservation, momentum

Thread Tools
Display Modes

Similar Physics Forum Discussions
Thread Thread Starter Forum Replies Last Post
conservation of angular momentum amirshrestha Kinematics and Dynamics 2 Apr 28th 2012 11:49 AM
conservation of angular momentum hapflir Advanced Mechanics 5 Oct 13th 2009 10:38 PM
Angular momentum conservation violation? physicsquest Advanced Mechanics 10 Jun 13th 2009 12:31 AM
Conservation of Angular Momentum monomoco Advanced Mechanics 1 Mar 15th 2009 10:45 PM
angular conservation of momentum/collision orgoistough Advanced Mechanics 1 Oct 31st 2008 09:14 PM

Facebook Twitter Google+ RSS Feed