Dear Jason, Thanks a lot! It seems to be my program, rather than *kinetic energy*.
The sample which did not work was my ‚Wackelstein‘, where there seem to be many other issues, the geometry is probably too difficult for me. I tried it on my 2D *rolling disc on an uneven street*, where the geometry is much simpler. There the total energy is constant also if the center of mass != geometric center. It seems to run into numeric difficulties ( a different issue), but outside those difficulties the total energy is constant. Better my program is wrong than *kinetic energy*! :-) Thanks again! Peter On Sat 25. Jun 2022 at 14:26 Jason Moore <moorepa...@gmail.com> wrote: > Peter, > > You should be able to provide the inertia (I, P) about a point P other > than the mass center of the rigid body. So in your code "mass center" does > not have to equal "P". But, I never really do that so it could be that the > underlying code doesn't apply the parallel axis theorem correctly. It isn't > a feature that is likely used much, if at all. If you have an example that > shows it doesn't work, then providing that on the SymPy issue tracker would > be helpful so we can find and fix the bug. > > Jason > moorepants.info > +01 530-601-9791 > > > On Thu, Jun 23, 2022 at 1:44 PM Peter Stahlecker < > peter.stahlec...@gmail.com> wrote: > >> I = me.inertia(A, iXX….) gives the inertia in the (normally) body - >> fixed frame A >> Body = Me.RigidBody( ‚Body‘, mass center, frame, mass, ( I, P)) >> >> My question: Does RigidBody ‚assume‘, that mass center = P ? >> >> Reason behind my question: >> For regular homogenious bodies, iXX, IYY, etc are often known relative >> to the geometric center of the body. >> If the mass center is not equal to the geometric center of the body, >> would RigidBody know, that the inertia is relative to the geometric center? >> >> In my program, the kinetic energy comes out right, if I set mass center = >> geometric center, but incorrect if I do not. >> Therefore, I wonder, whether there is a mistake in my program, or whether >> RigidBody assumes that P = mass center. >> >> Thanks a lot for any help! >> >> >> -- >> You received this message because you are subscribed to the Google Groups >> "sympy" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to sympy+unsubscr...@googlegroups.com. > > >> To view this discussion on the web visit >> https://groups.google.com/d/msgid/sympy/0d3101eb-1fe7-4c24-a125-bab8c8a58145n%40googlegroups.com >> <https://groups.google.com/d/msgid/sympy/0d3101eb-1fe7-4c24-a125-bab8c8a58145n%40googlegroups.com?utm_medium=email&utm_source=footer> >> . >> > -- > You received this message because you are subscribed to the Google Groups > "sympy" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to sympy+unsubscr...@googlegroups.com. > To view this discussion on the web visit > https://groups.google.com/d/msgid/sympy/CAP7f1Ag%2BpEFeUUs%3Duvn8V8enFmm4F6z9m4h6JEfRFXR-q0SEdg%40mail.gmail.com > <https://groups.google.com/d/msgid/sympy/CAP7f1Ag%2BpEFeUUs%3Duvn8V8enFmm4F6z9m4h6JEfRFXR-q0SEdg%40mail.gmail.com?utm_medium=email&utm_source=footer> > . > -- Best regards, Peter Stahlecker -- You received this message because you are subscribed to the Google Groups "sympy" group. To unsubscribe from this group and stop receiving emails from it, send an email to sympy+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/sympy/CABKqA0YhojimUm4DoaEzXQ7WO%2BVVuNFgYEW4GxN7w9toXu0ZSg%40mail.gmail.com.
