Re: [Phys-l] Interactive Physics Simulations

[Brian Whatcott <betwys1@sbcglobal.net>]

At 10:49 AM 10/12/2006, Jeff Schnick,  you wrote:

> In Engineering Mechanics, Dynamics, Pearson Prentice Hall 2004, 10th
> Edition; R.C. Hibbeler, defines a coefficient of restitution e ///
> as the difference in the speeds of the colliding objects after the
> collision to the difference in the speeds of the colliding objects
> before the collision.
> When this ratio is zero, Hibbeler calls the
> impact plastic or inelastic and says that the objects stick together.
> In such a case there is a period of deformation but there is no
> subsequent restitution.  When the ratio is 1,  Hibbeler calls the
> collision perfectly elastic.  He uses the adjective for the elastic
> case.
>  To me this implies that for 0 > e > 1 the collision is partially
> elastic meaning there is some restitution but one or both of the objects
> fail to recover their original shape.  Thus, for an elastic collision, e
> > 0; and if the collision is perfectly elastic, e=1.  This suggests that
> the "totally" in the expression "totally inelastic collision" is
> redundant.  I am a fan of the redundancy in this case.
>
> The total momentum of the system is the same before and after the
> collision, only in the idealized case of the perfectly elastic collision
> can the same be said for the macroscopic kinetic energy of the system.
>
> Jeff Schnick

I had a reservation about this detail of Jeff's exposition:
 "...the collision is partially
elastic meaning there is some restitution but one or both of the objects
fail to recover their original shape.  "

I visualized  a variety of materials that reconstitute their original shape,
 but so slowly as to provide largely inelastic collisions.

This quibble might be addressed by adding the word "immediately"
as in....
 "...the collision is partially
elastic meaning there is some restitution but one or both of the objects
fail  to immediately recover their original shape. "

Brian Whatcott    Altus OK    Eureka!