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NEWTON(6D)							    NEWTON(6D)

NAME    [Toc]    [Back]

     newton - a	physical modeling demo

SYNOPSIS    [Toc]    [Back]

     newton [-f	model_catalog] [-D]

DESCRIPTION    [Toc]    [Back]

     Newton is a real-time simulation of an elastic body.  Command-line
     arguments will be discussed below,	after a	general	explanation of the

     The body is made up of a number of	atoms and springs.  Atoms are points
     of	mass for which the forces of gravity apply.  Between some pairs	of
     atoms, there are springs, which supply additional forces if their current
     length is different from their initial length.  The specific spring
     equation used is not linear, but behaves close to linear in a narrow
     vicinity of the initial spring length.

     The main window of	Newton shows a cubic room that contains	the elastic
     model at its center.  To drop the model, press and	release	the left mouse
     button.  Between the time you press the left mouse	button and the time
     you release it, you get a chance to reorient the model any	way you	want -
     just move the mouse around	and the	model will turn	in that	direction.
     Independently, you	may wish to rotate the room.  This can be achieved by
     pressing the middle mouse button and moving the mouse around.  To stop
     reorienting the room, let go of the middle	mouse button.

     Whenever you want to re-drop the model, hit the left mouse	button.	 As
     before, you get a chance to reorient the model prior to dropping it (you
     drop it by	releasing the left mouse button).

     MENUS    [Toc]    [Back]

     As	usual with the GL demo programs, the right mouse button	is the menu
     button.  Several menu selections are available:

     models	  There	are a number of	different models to select from, and a
		  different shape can be selected via the model	catalog	menu.

     physics	  The simulation is controlled by several physical parameters,
		  and they can all be changed by the user.  For	example, if
		  the user wants to increase the gravity (essentially, make
		  the model heavier), all she has to do	is select ``gravity''
		  in the ``physics'' submenu, and a gravity slider will	pop
		  up.  See the section on sliders below	to find	out what
		  physical parameters are available, and how to	use the

     model display
		  The model can	be displayed in	several	fashions:

									Page 1

NEWTON(6D)							    NEWTON(6D)

		  smooth surfaces
				Display	the model as a single surface, using
				the lighting model to obscure the corners of
				the body;

		  flat surfaces	The normal display mode	for most models.
				Every surface is lit independently;

		  springs	Display	the internal connections between the
				``atoms'' of the model;

		  Bermuda	This is	a weird	display	mode using the color
				map, try it!

		  NOTE:	Only one of the	above four is possible at any given
		  time,	so if you are tired of the Bermuda display mode, the
		  way to return	to a more normal display mode is to simply
		  select flat surfaces,	smooth surfaces, or springs from this

		  toggle translucency
				The model can be made either opaque or
				transparent.  Consecutive selections of	this
				menu item toggle between these two

		  toggle surfaces+springs
				It is sometimes	helpful	to see both the
				surfaces and the springs of the	model at the
				same time.  If you have	selected either	flat
				or smooth surfaces, and	you want to
				superimpose the	springs, click this menu item.
				Clicking it again cancels the springs.	This
				is particularly	useful if the model is made
				transparent, using the previous	menu item.

     room display This controls	the way	the room itself	is drawn.  Selections
		  are either lighted walls w/ shadows, which means the walls
		  are lit (just	like the model itself,)	and the	model casts
		  shadows on them; lighted walls w/o shadows, which is faster
		  (since there are less	polygons that need to be drawn); and
		  pinball walls	, which	are non-lit walls, but rather walls
		  that light up	whenever the model hits	them (the color
		  represents the amount	of displacement).

     spin mode on/off
		  As with many GL demos, there is a mode in which things
		  happen ``by themselves'' without user	intervention.  Turning
		  spin mode on causes the room to continually follow the
		  mouse, rotating in the mouse direction with a	velocity
		  proportional to the distance from the	mouse position to the
		  center of the	screen (not the	model window).

									Page 2

NEWTON(6D)							    NEWTON(6D)

		  Quit Newton. Other ways of quitting include hitting the
		  ESCAPE key, and selecting quit from the menu bar.

     SLIDERS    [Toc]    [Back]

     A slider is a means of changing the value of some physical	parameter of
     the system.  If the slider	you need is not	open already, you can open it
     from the physics menu, as explained above.	 A slider is essentially a
     window that shows the lowest, highest, and	current	values of the
     corresponding physical parameter:	the precise values appear in the lower
     left, lower right,	and lower middle of the	slider window.	A visual
     interpretation appears above the numbers as a rectangle that is
     partitioned into a	green and yellow sections, which correspond to the
     portion of	the range below	and above the current value, respectively.

     Moving to any point within	the graphic representation of the slider and
     clicking the left mouse button will make the value	corresponding to that
     point become the current value of the slider.  You	can also slide the
     value by using the	middle mouse button in a manner	analogous to rotating
     the room (see above).  The	right mouse button brings up the slider	menu,
     which enables you to reset	the slider to its default value, or close the
     slider window altogether.	Once closed, a slider window can be reopened
     from the physics menu.

     Available sliders are:

     Gravity	    The	magnitude of the gravity vector.  It always points
		    down (in screen space).

     Spring Constant    [Toc]    [Back]
		    The	spring constant	of the stiffest	spring in the model.

     Wall Stiffness The	walls of the room are like trampolines,	and that is
		    why	the model bounces off of them.	This parameter
		    controls the stiffness of those trampolines.  The higher
		    the	value, the harder the walls kick back.	The lower the
		    value, the soggier the walls.  The latter results in the
		    model ``sinking'' into the walls.

     Wall Friction  When the model hits	a wall,	it typically loses some	energy
		    due	to wall	friction.  This	parameter controls which
		    fraction of	the energy is lost.  The higher	the friction,
		    the	more energy gets lost.	Note that with high friction
		    the	model often ``prefers''	``jumping'' along a wall to
		    ``sliding''	along it.

     Air Dampening  This parameter controls how	much energy the	model loses
		    simply by moving through the air that's inside the room.
		    When this value is high, it	is as if the model is
		    surrounded by a viscos material (such as honey) rather
		    than air.  When this value is zero,	the model experiences

									Page 3

NEWTON(6D)							    NEWTON(6D)

		    no air resistance whatsoever.

     Display Step   If you think of what you see on the	screen as a movie,
		    this parameter controls which frames actually get drawn.
		    When the display step is 5,	for example, only every	fifth
		    frame (roughly) of the movie gets displayed.  When the
		    value is high, the animation is usually faster and
		    jumpier.  When the value is	low, the movie is more smooth,
		    but	has a feeling of slow motion.

     COMMAND LINE ARGUMENTS    [Toc]    [Back]

     The -D (demo-mode)	option causes all the sliders to be opened (as well as
     the main window) in pre-defined positions on the screen.  Specifiying
     ``-f model_catalog'' causes the program to	use an alternative list	of
     model shapes instead of the default ones.	The serious user may
     experiment	with new model shapes once she managed to decipher the obscure
     format of a model description file...

     A model catalog is	a list of model	description file names.	 If a name is
     not fully-qualified, it is	considered relative to the directory
     containing	the model catalog file.

     If	the model_catalog is `-', it is	taken to be the	standard input.	 For
     example, to have Newton run on all	the ``*.j'' files in the current
     working directory,	you might use

	  echo	 *.j   |   newton   -f	 -

     HELPFUL HINTS    [Toc]    [Back]

     There are many fun	things to do with this program.	 However, remember
     that certain combinations of physical parameters may cause	the model to
     break - very much as in real life.	 When the model	breaks,	there is no
     need for panic: simply hit	the left mouse button and you get a fresh
     model that	you can	break again ...

     You can kick the model by tilting the room	so the lowest point is a
     corner.  Let the model come to a rest at that corner, and then rotate the
     room around a horizontal axis - simply drag the mouse either up or	down
     rapidly with the middle mouse button pressed.  The	decision whether to go
     up	or down	depends	on the position	of the low corner: if it is more to
     the front (facing you) - go up, if	it is facing away from you - go	down.
     Kicking normally introduces gobs of energy	into the system, and some
     models do not handle that very well.  You may want	to decrease wall
     stiffness or increase spring constant before kicking.

     Another fun thing is to see soggy walls:  just push wall stiffness	to a
     very low value, and then drop the model.  This is particularly visible if
     you align the room	so that	the bottom wall	is almost flat,	but still
     faces you a little	(if a wall faces away from you - it automatically
     becomes transparent) prior	to dropping the	model.	When the model comes

									Page 4

NEWTON(6D)							    NEWTON(6D)

     to	a rest,	you may	kick up	the wall stiffnes (select the default wall
     stiffness from the	slider menu), and the model will soar to the sky as
     fast as gravity and the air dampening enable.

     Once you have mastered the	user interface to this program,	try to get the
     chain model to hang in free space by its two endpoints.  In other words,
     get the room aligned so that there	is an edge of the cube at the bottom,
     and the two walls incident	on that	edge form a V-shaped corner.  Then
     drop the model.  Wall friction and	stiffness may help you overcome
     inacuracies in the	room alignment.	 Once the model	hangs there, you can
     gradually lower and raise the spring constant, lower and raise gravity,
     or	kick the wall stiffness	- all of which will show amusing effects on
     the chain.

     These are but a few of the	possible experiments that can be carried out
     using this	simulation.

FILES    [Toc]    [Back]

     /usr/demos/General_Demos/newton/data	  the default list of model
     /usr/demos/General_Demos/newton/data/*.j	  model	description files

DIAGNOSITICS    [Toc]    [Back]

     Self explanatory.	Messages that appear on	the terminal from which	Newton
     was invoked indicate a problem Newton is experiencing in performing the
     simulation.  Typically, this indicates an incorrect setup of either the
     Newton program or the catalog or description files.

BUGS    [Toc]    [Back]

     The bending of the	walls is approximated by a crude pyramid.  The sheet
     model particularly	suffers	from that, so you have to have relatively
     stiff walls to get	a decent performance out of the	sheet.

AUTHOR    [Toc]    [Back]

     Yossi Friedman, June-August 1988.	The idea is derived from the original
     ``Jello'' by Thant	Tessman.

									PPPPaaaaggggeeee 5555
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