So I've been reading all of the emails. I had this idea about using the pen. When the pendulum was swinging if the pen was down, it would draw the arc. However, it wouldn't look like the Robolab one (at least not yet) but could it evenutally? Just a thought as I was sitting in traffic on the way home tonite.

Robyn

Hi Phil --

At 5:38 PM -0400 4/17/03, Phil Firsenbaum wrote:

Interesting...I actually saw this message on the Squeak archive. i didn't receive it on the mailing list, though.

Anyhow, even if the pen were down and the pendulum simulated reality i think it would draw lines on top of lines unless the area under the pen was scrolling. Do you see what I mean?

Well, here's a little exercise in relativized thinking ...

Embed a round little object like an ellipse to be the bob of the pendulum, call it "bob". Make another little object called "plotter", put its pen down. See what happens when you do:

plotter's y increase by 1 plotter's x <- bob's x

Cheers,

Alan

I'm still hoping to get the pendulum to work although maybe that's not as important as the thinking about pendulum that I've been forced to do. I think it would be really powerful to get kids involved. We should try it out before the year is out...with something that's doable, or maybe not Wouldn't it be nice to have at least a few other teachers involved in this conversation? From PS 87 or from the local PDS? Is there a grant opportunity lurking in here someplace?

Off to a Seder now...enjoy! Phil

On Wednesday, April 16, 2003, at 07:23 PM, Robyn Ulzheimer wrote:

...

So I've been reading all of the emails. I had this idea about using the pen. When the pendulum was swinging if the pen was down, it would draw the arc. However, it wouldn't look like the Robolab one (at least not yet) but could it evenutally? Just a thought as I was sitting in traffic on the way home tonite.

Robyn

--

Hi Bert --

That is a very good point! I'd forgotten that embedding makes an object live in the coordinate system of its owner -- and that is what it is supposed to do. However, it's clear from this and other examples that I can think of that this perhaps should be the default, but it might be a good idea to put a flag on a player to "use the coordinate system that its owner uses".

Let me think about this over the weekend ...

Cheers,

Alan

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At 1:40 PM +0200 4/19/03, Bert Freudenberg wrote:

Am Freitag, 18.04.03 um 22:51 Uhr schrieb Alan Kay:

...

Hi Phil --

At 5:38 PM -0400 4/17/03, Phil Firsenbaum wrote:

...

Interesting...I actually saw this message on the Squeak archive. i didn't receive it on the mailing list, though.

Anyhow, even if the pen were down and the pendulum simulated reality i think it would draw lines on top of lines unless the area under the pen was scrolling. Do you see what I mean?

Well, here's a little exercise in relativized thinking ...

Embed a round little object like an ellipse to be the bob of the pendulum, call it "bob". Make another little object called "plotter", put its pen down. See what happens when you do:

            plotter's y increase by 1
            plotter's x <- bob's x

"Relativized thinking" is fine, but the implementation is itself relative, so this does not work.

After embedding, the bob lives in the coordinate system of its parent, the pendulum. Rotating the pendulum does nothing to the bob

• just look at its geometry category, it's static. I then tried

using a PolygonMorph as pendulum because it does not use a TransformMorph, but then, the transform of the embedded bob goes wild (try it).

The latter behavior looks like a bug, while the former is probably supposed to behave like this. We would have to introduce a "global" or "absolute" position to make this work.

-- Bert

--

I agree. I'm not interested in a frame by frame animation, because it wouldn't simulate the reality of a pendulum. I do want to avoid the trig but I'm not sure I see how I'd "weigh" the forces of gravity at different angles...hope I can figure it out. Phil

On Tuesday, April 15, 2003, at 07:02 PM, Alan Kay wrote:

What's the model behind the "movin' pictures"?

The simple frame by frame animation has a very weak and almost nonexistent model.

But, as you've seen from our demos and the DVD documentary, even 5th graders can figure out the two line script that represents an excellent 2nd order differential equation of the (almost) constant accelleration of gravity near the surface of the earth. This is what drives a real pendulum.

Now you just have to "see" how the downwards and sideways forces change with the position of the pendulum and you can easily make a real model of it.

Enclosed is a project that has noticed that the rotational force is proportional to the sine of the angle of the pendulum. But, there is a nice way to bypass trig completely by directly "weighing" the forces exerted by gravity at different angles ... heh heh ...

Cheers,

Alan

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At 3:23 PM -0400 4/15/03, Brucestro@aol.com wrote:

Andreas/Phil,

Wouldn't another possilble approach be to create a series of pictures showing all the possible positions of the pendulum and then control it as one would control a cartoon/movie?? (Phil - There are examples of this technique at squeakland.org under the eToys link.)? Another option that comes to mind is to stack each of these pictures on top of each other and move them front to back as required.? Andreas, I'm new to Squeak -- would these ideas work, or am I on the wrong track?

Thanks, Bruce Strothenke Teachers College Columbia University

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