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Remaining Work
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When you select earth or space, there is a part of the right side that stays dark blue.
If you widen the window in any background, the right part stays blue too.

6.  Is it possible to give the skater any velocity when he's in space?  I
thought there used to be a way but I can't figure it out.
Draggable jet pack, to apply velocity.

Can we put up a button on the screen when the skater has exited the screen: "Return Skater"?

Optional to overlay a position-grid on the real space (to correlate with graph).
    Like moving man, force1d or ramps, disabled by default.

Put coefficient of friction in an advanced button.

Zoomable Energy vs Position graphs.

Bug: Setting record, then live, then record resets to last record state.

Add clipping to energy vs position plot (so data doesn't fall outside the data area).

[internal] Figure out the meaning of the magic grab number in EnergyConservationModel

Maybe "Live" should be changed to "Go" instead of "Play"

Bug: clear button erroneously shows 'this simulation is paused' when it is not.

Bug: The measuring tape's initial readout is incorrect.

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Low Priority
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User-selectable skater/vehicle graphics.
Crashing skater?

add spanish

Add game-ish modes to sk8r application
	. 2-skater mode
	. Grab the apple?
	. Jump the buses?

Bug: When user drags track that skater is resting on, the skater doesn't move with it.
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One solution (which I think would be nice) ... would be to have the
optional grid on the play area and then the show the same grid on the
energy vs position graphs... so if the grid spacing were every meter
then there would be a faint grid in the background of the plot as
well as the background of the play area that was every meter.  This
way they don't have to be the same "scale" but you can still make the
connection.  The ruler and the graph match so it seems like it
wouldn't be that hard program wise???

Another bug ...
The sim was running in the background for the last hour or so, and
now when I bring it to the foreground I can't get it to redraw it's
screen .. it's all white until I mouse over sections, but even then
it's erratic whether it will redraw or not.
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I can't remember the idea exactly, but looking at the sim again, I do
think it would be a good option... not a default.  It will allow you
to make nice tracks ... e.g. if I start the guy at this line then he
will only rise to that same line or he will get over the hill as long
as the hill is below that line... it gives you reference heights ...
I would make them some nice increments.. like every 1 or 2 meters,
and make them pretty dim.

In my brief play I found a bug ... in the attached screen shot the
skater doesn't fall off the track even though he gets completely off the edge.
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Bug: The dragging constraints are not skater-centric; after dragging against a constraint,
the mouse is no longer directly over the skater.