Easy collision problem

d000hg · 2002-03-13T05:41:59

Ok, two rigid bars of length l1, l2 and masses m1 and m2. They have linear velocities v1 and v2 as vectors in 3d space. They have angular velocities w1 and w2. My questions: 1)w should be a vector, but how is it specified so I know what axis the bar is spinning about. 2)I detect that the two bars collide. The collision point is at point x1 on bar1 and x2 on bar2. I know from basic mechanics that momentum must be conserved, and energy loss is modelled using a restitution coeeficient (e=final relative velocity/original relative velocity, right?) But what about angular considerations? At first I though angular momentum had to be conserved, but imagine a brick thrown at the end of a pole - initially there''s only linear momentum, afterwars there''s angular motion too. If the collision is at the midpoint of the bar then there will be no angular effect, but how does one calculate the impulse in this situation, and how do you apply impulse in a rotational frame? 3)If the collision is right at the end of the bar, that doesn''t mean the bar will spin but not move, but what proportion of the energy will be rotational and what proportion linear, kinetic energy. Thanks.

Math and Physics Programming

Started by d000hg March 06, 2002 11:53 AM

10 comments, last by d000hg 22 years, 11 months ago

Dobbs

164

March 12, 2002 01:44 PM

Thought of a better argument against conservation of angular momentum:
I run towards a roundabout and jump on. I change from travelling in a straight line to travelling in a circle. Maybe it''s the sum of angular and linear momentum that''s conserved?

What are you saying, there''s no such thing as conservation of linear and angular momentum? Think about your example. It''s not just you and a roundabout with angular and linear momentum, it''s you, a roundabout, and everything else attached (the Earth).