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*From*: "LaMontagne, Bob" <RLAMONT@providence.edu>*Date*: Mon, 31 Dec 2007 12:39:58 -0500

Ludwik,

You seem to be repeating the same thing over and over expecting hoping to get different results.

Personally, I don't trust Interactive Physics - I prefer to program a problem in Fortran or C. However, try using the random number generator in I.P. to produce a series of small disturbances at random times and random directions. A single disturbance has to change the orbit. Real orbits are subject to both random and periodic disturbances.

Bob at PC

________________________________

From: phys-l-bounces@carnot.physics.buffalo.edu on behalf of Ludwik Kowalski

Sent: Sun 12/30/2007 9:45 PM

To: Forum for Physics Educators

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

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/

_______________________________________________

Forum for Physics Educators

Phys-l@carnot.physics.buffalo.edu

https://carnot.physics.buffalo.edu/mailman/listinfo/phys-l

**Follow-Ups**:**Re: [Phys-l] Simulating a disturbance of a stable planetary system.***From:*John Mallinckrodt <ajm@csupomona.edu>

**References**:**[Phys-l] two questions***From:*"Anthony Lapinski" <Anthony_Lapinski@pds.org>

**Re: [Phys-l] [tap-l] two questions***From:*William Beaty <billb@eskimo.com>

**[Phys-l] Sharing a problem for students***From:*Ludwik Kowalski <kowalskil@mail.montclair.edu>

**Re: [Phys-l] Sharing a problem for students***From:*Ludwik Kowalski <kowalskil@mail.montclair.edu>

**Re: [Phys-l] Sharing a problem for students***From:*Ludwik Kowalski <kowalskil@mail.montclair.edu>

**Re: [Phys-l] Sharing a problem for students***From:*"Bob Sciamanda" <trebor@winbeam.com>

**Re: [Phys-l] Sharing a problem for students***From:*Ludwik Kowalski <kowalskil@mail.montclair.edu>

**[Phys-l] A numerical simulation of orbiting***From:*Ludwik Kowalski <kowalskil@mail.montclair.edu>

**Re: [Phys-l] A numerical simulation of orbiting***From:*John Denker <jsd@av8n.com>

**Re: [Phys-l] A numerical simulation of orbiting***From:*Ludwik Kowalski <kowalskil@mail.montclair.edu>

**Re: [Phys-l] A numerical simulation of orbiting***From:*John Denker <jsd@av8n.com>

**Re: [Phys-l] A numerical simulation of orbiting***From:*Ludwik Kowalski <kowalskil@mail.montclair.edu>

**Re: [Phys-l] A numerical simulation of orbiting***From:*John Mallinckrodt <ajm@csupomona.edu>

**Re: [Phys-l] A numerical simulation of orbiting***From:*Ludwik Kowalski <kowalskil@mail.montclair.edu>

**Re: [Phys-l] A numerical simulation of orbiting***From:*John Mallinckrodt <ajm@csupomona.edu>

**[Phys-l] Simulating a disturbance of a stable planetary system.***From:*Ludwik Kowalski <kowalskil@mail.montclair.edu>

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