"Andrew" <ast### [at] hotmailcom> wrote in message
news:3d95a832@news.povray.org...
> You have the right idea about what the inverse-square law means,

Well, that's *something*!

> The P=Q problem is easily solved since P and Q are points, but the
> objects in question are not.  If they are spheres, then P and Q
> represent the centres, so unless the spheres are infinitely small, then
> P and Q can never be equal.

Thinking about it, I realised that in my particular scene the ball is
prevented from reaching the magnet anyway - I just forgot to put this into
the math! (Ooops...)

> The problem with units arises because the force is *proportional* to,
> not equal to, S / vlength(P-Q)^2.  A constant of proportionality is
> needed, which obviously depends on the units.

Now we're making sense...

>  For example,
> gravitational force is F = (G * m(1) * m(2)) / r^2.  Here r is the
> distance between the two masses, and m(1) and m(2) are the masses of
> each object.  G is the constant of proportionality, equal to 6.67E-11
> when the masses are in kilos and the distance is in metres.

Right... So since the Earth's mass is so large, the force of gravity is more
or less exactly equal to 9.8006 * m(2)? (Well, at sea level anyway!)

Interestingly, that seems to answer another of my questions - if this is
right, and if magnets are similar, then the force of the magnet would indeed
depend on the size of the magnetic ball it's pulling... (Of course, since F
= M * A, that means that at a given distance the acceleration due to the
magnet is more or less constant... I think! Maybe I'm getting out of my
depth here 8-|... )

> PS magnets are nasty to work out, as they must have both poles, and
> therefore a complicated field.  Use a charged ball to think about
> instead - it only has one polarity to worry about!

Ooo blimey, there's no way I'm gonna bother with putting poles on them!
LOL... I just wanted a fairly abstract concept of a point in space that
pulls matter towards it acording to the inverse square law.

Let's try again...
Andrew.

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