EField allows the creation of point charges as well as geometric
shapes using the add object method:
The first argument is the name of the object to be added, and
the second is a comma-delimited list of parameters. A circle can be added
to either applet using the following JavaScript statement:
id=document.physletname.addObject("circle", "x=0,y=-1.0,r=10");.
The addObject method is very forgiving
since not all parameters need to be specified. Default values are overridden
only if the parameter appears in the list. Incorrect and unsupported parameters
do not affect the applet and are ignored.
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Name
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Attributes
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arrow
Arrows are often animation slaves of other objects. They can
represent almost any vector since the h and v components can be functions
of the variables.
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x- double x position of
the base in world units
y- double y position of the base in world units.
h- string horizontal component as a function of t, x, y, vx, vy,
ax, and ay.
v- string vertical component as a function of t, x, y, vx, vy, ax,
and ay.
s- int the size of the head in pixels
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box
a box is a hollow rectangle.
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x- double x position
of the center in world units
y- double y position of the center in world units
h- int height in pixels
w- int width in pixels
m-double the mass
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caption
text that is centered near the top of the screen.
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x- double x position
of the center in world units
y- double y position of the center in world units.
text- string text of the caption
calc- string A function of t to be evaluated at every time step.
The value of the function is displayed to the right of the text.
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charge
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x- double x position
of the center in world units
y- double y position of the center in world units.
q- double object's charge.
r- int radius in pixels
m-double the mass
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circle
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x- double x position
of the center in world units
y- double y position of the center in world units.
r- int radius in pixels
m-double the mass
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connectorline
a straight line connection two objects.
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id1- int first object
identifier.
id2- int second object identifier.
See also: addConnectorSpring(int,int) in the online documentation.
This method is easier to use if the ids are stored as integers.
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connectorspring
a spring connection two objects.
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id1- int first object
identifier.
id2- int second object identifier.
See also: addConnectorLine(int,int) in the online documentation. This
method is easier to use if the ids are stored as integers.
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cursor
a circle with cross hairs.
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x- double x position
of the center in world units
y- double y position of the center in world units
r- int radius in pixels
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image
a gif image. The coordinates are the coordinates of the upper
left hand corner.
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x- double x position
of the left side in world units
y- double y position of the top in world units
file- string name of the gif file. The image should be in located
in the same directory as the jar file for the applet.
m-double the mass
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line
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x- double x position
of the base in world units
y- double y position of the base in world units.
h- string horizontal component as a function of t, x, y, vx, vy,
ax, and ay.
v- string vertical component as a function of t, x, y, vx, vy, ax,
and ay.
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rectangle
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x- double x position
of the center in world units
y- double y position of the center in world units.
h- int height in pixels.
w- int width in pixels.
m-double the mass
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relshape
draws an arbitrary shape by connect-the-dots. The shape is specified
by passing the relative pixel positions of the dots starting at x and y.
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x- double x position
of the center in world units
y- double y position of the center in world units.
n- int number of vertices in the polygon.
hStr- string A comma separated list of the x postions of the relative
vertices in pixel units.
vStr- string A comma separated list of the y postions of the relative
vertices in pixel units.
m-double the mass
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shell
a circle with a hollow center
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x- double x position
of the center in world units
y- double y position of the center in world units
r- int radius in pixels
m-double the mass
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testcharge
a charge that is free to move under the action of fixed charges and
an external potential.
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x- double x position
of the center in world units
y- double y position of the center in world units
vx- double x velocity in world units
vy- double y velocity in world units
q- double object's charge
r- int radius in pixels
m-double the mass
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text
a fixed text string followed by an optional calculation.
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x- double x position
of the left side of the text in world units
y- double y position of the top of the text in world units
text- string static text.
calc- string A function of t, x, y, vx, vy, ax, and ay that is evaluated
at every time step. The value of the function is displayed to the
right of the static text.]
Note: Use the setFormat method to change the decimal format used to output the calculation.
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