eToys surprises

hjh-sqlist at lexdb.net hjh-sqlist at lexdb.net
Fri Dec 24 09:03:52 UTC 2004


Hi 

The Newtonian orbits screen is impressive. I'd like to learn how that is done.
I see that now variables are possible in eToys. The last time I looked into
eToys (some time ago..) this wasn't possible.  Is there a tutorial or a short
movie which shows how to use them? How do I define them?

On http://www.squeakland.org/author/etoys.html in particular (e.g. quickstart
guide) I do not see anything like that.

Hannes


Quoting Alan Kay <alan.kay at squeakland.org>:

> It is also very easy to do Newtonian orbits in etoys, if full precision is 
> used for acc, vel, and position properties. The script looks just as one 
> would like: do this in a playfield with origin at center, place the sun 
> there, and the vector distance of the earth is also its distance to the 
> sun. It's not science to claim inverse square, but it's one of the 
> plausible hypotheses with an analogy to the intensity of light. Newton 
> actually proved his stuff as math long before he got to the last books 
> where he looked to see how the phenomena in the world behaved. Given this 
> as an hypothesis, the script is straightforward: the strength of the force 
> being inversely proportional to the square of the distance, and the 
> direction of the accelleration is the opposite direction of the vector that 
> is the Earth.
> 
> Cheers,
> 
> Alan
> 





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