The discussion revolves around the concept of reference frames in the context of elastic collisions between two balls (Ball 1 and Ball 2). Participants explore whether there exists a reference frame in which Ball 2 can be considered fixed at rest throughout the collision process, including before and after the collision.
Participants express disagreement regarding the existence of an inertial reference frame in which Ball 2 is always fixed. While some acknowledge the rest frame of Ball 2, others argue that it does not function effectively as an inertial frame, leading to unresolved questions about the nature of reference frames in collision scenarios.
There are limitations in the discussion regarding the definitions of inertial and non-inertial frames, as well as the assumptions about relative velocity during collisions. The implications of these definitions on the analysis of the collision remain unresolved.
Yes, the rest frame of Ball 2 is such a frame of reference (surprise!), but it is not inertial and therefore not necessarily a good choice to describe the process.feynman1 said:Is there any sort of reference frame in which Ball 2 is always fixed (at rest) so that one can look at their relative velocity always in that reference frame?
Do you mean it's not inertial at the instant of the collision but inertial before and after? If so, Ball 2 won't be fixed in that frame, which isn't what I look for.DrStupid said:Yes, the rest frame of Ball 2 is such a frame of reference (surprise!), but it is not inertial and therefore not necessarily a good choice to describe the process.
Relative velocity is per definition the velocity of ball A in the rest frame of ball B (or vice versa). But if the relative velocity doesn't change, then there is not much of a collision.feynman1 said:2 balls (Ball 1 and Ball 2) collide fully elastically and their relative velocity stays the same as that before the collision. Is there any sort of reference frame in which Ball 2 is always fixed (at rest) so that one can look at their relative velocity always in that reference frame? Here 'always' includes before and after the collision.
It is not inertial at the instant of the collision because Ball 2 (which is accelerated during the collision) is fixed in that frame.feynman1 said:Do you mean it's not inertial at the instant of the collision but inertial before and after? If so, Ball 2 won't be fixed in that frame, which isn't what I look for.
Just edited the original question, relative v changes sign.A.T. said:Relative velocity is per definition the velocity of ball A in the rest frame of ball B (or vice versa). But if the relative velocity doesn't change, then there is not much of a collision.
Right, then have you an answer to the original question?DrStupid said:It is not inertial at the instant of the collision because Ball 2 (which is accelerated during the collision) is fixed in that frame.
He already answered it in post 2!feynman1 said:Right, then have you an answer to the original question?
I knew all along that such a frame written in post 2 doesn't work well. Then can we conclude that there's no inertial reference frame in which Ball 2 is always fixed?Dale said:He already answered it in post 2!
Yes.feynman1 said:Then can we conclude that there's no inertial reference frame in which Ball 2 is always fixed?