[Phys-l] Simulating a disturbance of a stable planetary system.

[Ludwik Kowalski <kowalskil@mail.montclair.edu>]

On Dec 30, 2007, at 7:16 PM, John Mallinckrodt wrote:

> . . . An IP simulation will easily demonstrate this fact in a
> minute or two and it will not be a computational artifact. . . .

That issue emerged from my failure to demonstrate stability of a simple 
two body system (a single planet revolving the sun along a circular 
trajectory). We expect such system to be stable (persistent). Using the 
I.P. (Interactive Physics) I simulated the system and a short 
disturbance. Someone wrote that stability means ability to recover 
after a disturbance. In my simulation the new orbit (after the 
disturbance) was significantly different from the orbit before the 
disturbance. The period of revolution of the new (elliptical) orbit 
turned out to be longer that period of revolution of the initial 
(circular) orbit. In other words, the disturbance I applied was not 
self-correcting.

The idea was to show that a disturbance applied to a two-body system is 
self-correcting while the same disturbance applied to the three-body 
system is not self-correcting. How to implement an I.P. disturbance 
whose consequences disappear after the disturbance is over? I changed 
the subject line of the thread because this question has nearly nothing 
to do with what has been discussed earlier today.
P.S. To trust results of an experiment one often tests instruments by 
performing control experiments. The two-body simulation was to be a 
control experiment before the three-body simulation. But I was stuck, 
as described in a message posted two days ago.
________________________________
Ludwik Kowalski, a retired physicist
5 Horizon Road, apt. 2702, Fort Lee, NJ, 07024, USA
Also an amateur journalist at http://csam.montclair.edu/~kowalski/cf/