Elastic rebound in physical simulations

Hi all,

Attached is a demo sim which shows that Real objects in a physical 
simulation don't always rebound correctly.  In the demo, it's usually a 
Mobile bouncing against a Stationary, but the same holds true for 
Mobile against Mobile.

The simulation drops Spheres, Cubes, PolygonDisks, and PolygonCones 
onto a Stationary base which is itself a Cube.  All objects have been 
called with their set-e and set-eT methods, setting those parameters to 
1.0 .  Using the inspector confirms that.  The dropped objects have not 
been given a rotation to start with.  A label shows up on each showing 
the rotation matrix as it moves.

Some observations:
1)  Any sphere just sits on the Base surface; no bounce at all.
2)  Any cube whose bottom face is entirely within the Base surface also 
just sits there; no bounce.
3)  Cubes whose bottom face overlaps the Base surface often fall 
through.
4)  Occasionally Cones also just sit there, but mostly they bounce at 
angles
5)  Same with Disks, I think (not sure I've seen any disks sit there).
6)  A Cone that bounces straight up doesn't bounce all the way back to 
the starting point, as
       an ideal elastic rebound would.

I think this gives the picture.

I realize that physical modeling isn't the primary objective of this 
environment.  So, perhaps this should be treated as an FYI to everyone.

Thanks for a great program, and for listening to comments so well!
Jim Grimes

P.S. please excuse some of the extra baggage which comes with this 
demo; I didn't take everything out of a much larger experiment.


___________________________________________________

Disclaimer:  Opinions stated herein are my own, and do not reflect 
policies or opinions of the Jet Propulsion Laboratory, NASA, or the 
California Institute of Technology.

James M Grimes                            Phone:  1-818-354-3890
Jet Propulsion Laboratory            Fax:       1-818-393-5239
Section 313 - Flight Systems       E-mail: [email protected]
Mailing  Address:                           Office Location: 301-475U
     Jet Propulsion Laboratory, M/S 301-486
     4800 Oak  Grove Drive
     PASADENA  CA 91109-8099

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