[PD] The Party at the Center of the Universe

[Mathieu Bouchard]

On Sun, 4 Dec 2005, Ed Kelly wrote:

> PMPD would be a good tool for exploring gravity - but you would have to
> explore the escape velocity scenario, where links (springs) are broken
> if an object attains a certain angular momentum, and a different
> (repulsive) mechanism comes into effect

It wouldn't be a good model because the ideal spring force is proportional
to distance, whereas gravitational force is inversely proportional to the 
square of the distance when assuming pointlike masses.

The only case where gravitational force is sort of (sort of!) like spring
force is if you go inside a large object of uniform density. obviously you
don't have orbits inside there.

Going over escape velocity does not change the nature of gravitation and
doesn't cause repulsion. Escape velocity is a natural consequence of the
inverse-square force (gravity or electricity).

The repulsion you are thinking of may be caused by centrifugal force, 
which only appears when the observer (the referential) is rotating.

Gravity works beyond escape velocity. It's just that beyond escape
velocity, it isn't dominant anymore. To compute gravity, you need to take
*all* of the possible particle pairs into account, so for N masses you
need N*(N-1)/2 springs, all of the time.

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| Mathieu Bouchard - tél:+1.514.383.3801 - http://artengine.ca/matju
| Freelance Digital Arts Engineer, Montréal QC Canada