nbody  (2009-Oct-03 20:33 EDT)

by <>  (2010-Sep-03 7:42 EDT)

I really like this one. Strangely it runs much faster in full-screen. More description would be helpful here as well.

by <>  (2010-Sep-03 7:42 EDT)

This project is a wonderful way to play with the gravitational attraction between two bodies. The longer you watch, the more interesting it gets. I like the fact that you can add extra siblings. I think that brief instructions on how to make a sibling would be helpful for those people who might not know.

by <>  (2010-Sep-03 7:42 EDT)

Come to think of it, this one should be kept in the old (wrong) form and I should have another one to show the difference. I'll revert this to an old version and make a new one.

by <>  (2010-Sep-03 7:42 EDT)

Ah, Randy, you're absolutely right and I was absolutely wrong. It was doing 1/r, not 1/r^2. I fixed it and uploaded a new version. This one now goes in relatively accurate elliptical orbits. Pretty cool and I regain faith in Etoys^^;

I'd stand by my statement on "fake"-ness, though. The unphysical slingshot effects is more prominent (as two objects get closer, the pull is even stronger, and at the next time step they are separated way too much to compensate it). But it could be used to explain the math behind physics. Or, explaining Kepler's law would be possible.

by <>  (2010-Sep-03 7:42 EDT)

Hi, Randy,

It I think is doing 1/r squared. "calc inner" script squares the diff in X and diff in Y and add them to divide the product of masses. and two smaller bodies are interacting each other. Shrink the big object by the yellow handle, and then adjust the simulation by changing the "coeff" (which is essentially "G"; if you shrink one, probably you should make coeff bigger). You can make siblings and can see each body are affecting each other.

Two body problem is failing because the time step is too coerce (I think...) Just make it to a two body problem, and open their viewers to set a large one's location at 0, 0, and set its speed to 0,0. Then for the smaller one, give a perpendicular speed. It should go in an elliptical orbit but make a regular but flower-like trajectory.

Fake as it is. ("simulation" means "fake", after all^^;) This simple constant time-step implementation causes unphysical sling-shot effects quite often, and it seems to me that the total energy in the system increases.

Thank you so much for the comment!

by <>  (2010-Sep-03 7:42 EDT)

Very intricate scripts. As far as I can determine the two smaller bodies don't interact with each other and the simulation is following 1/r law instead of Newton's 1/rsquared law. Maybe that is why your 2body problem failed. Is this why you call it "fake"? This could easily be changed if my observation is correct, but I could be missing something.

Nbody to physicists has a specific meaning, so it might be better to change the name unless you make it a true nbody simulation.

Clever use of Kedame.

by <>  (2010-Sep-03 7:42 EDT)

I tried a few more things by making a two-body simulation, and it is *not* clearly doing a good job. The perigee and apogee shift way too much. As I put "fake physics" as its tag, this kind of simulation can be dangerous for real physics...

by <>  (2010-Sep-03 7:42 EDT)

Very, very cool enhancements! I cranked up the project points :-)

Here's another idea for another project based off of this one:

Can you simulate the masses of our solar system? Anchoring the sun and showing the "orbits" of the planets. Not to precisely mimic our solar system orbital mechanics, but just the relative masses...

by <>  (2010-Sep-03 7:42 EDT)

Thank you jon,

I wanted to have the mass variation going when I made it. I revisited it and made it work and re-publish the project.

by <>  (2010-Sep-03 7:42 EDT)

Would be nice to add some visual effects, colors, different shapes and sizes to reflect different mass. For others, a good reference is here and here

by <>  (2010-Sep-03 7:42 EDT)

Thank you for the comments. I'd like to know what you meant by "real world application"...

by <>  (2010-Sep-03 7:42 EDT)

Rather mesmerizing in effect and intriguing in implementation.

Perhaps a later version of this would include some explanation of the mathematics or at least the computations behind this.

Also there's quite of bit of clever etoys know-how going on here, which people might want to study but which might benefit from some accompanying narrative.

Very cool project!

by <>  (2010-Sep-03 7:42 EDT)

High marks for technical merit, but maybe more description or possible real world application would help.

by <>  (2010-Sep-03 7:42 EDT)

(Yes, I cannot see other comments once I logged in.)

I think this one doesn't deserve to be featured. The others, "better nbody" and/or "3body" may be good but this one is just showing my learning curve and wrong simulation.