Dear Jason, There is nothing wrong with *kinetic energy*, at least I could not find anything!
I programmed a 3D ball rolling on a flat surface. The total energy is constant, no matter where the center of mass is. Sorry about the commotion I created! NB: I use solve_ivp to do the integration. I have to set max_step = 0.01 to get a constant total energy. If I do not do this, it is not constant. Peter On Sat 25. Jun 2022 at 18:15 Peter Stahlecker <[email protected]> wrote: > 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 <[email protected]> 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 < >> [email protected]> 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 [email protected]. >> >> >>> 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 [email protected]. >> 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 > -- 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 [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/sympy/CABKqA0btsFbOiyc1TiPqyRkBK1jwVxnRak6v%3DU%2B6urGDP%3DorSQ%40mail.gmail.com.
