changes:
made sliders and fields conform to my design preference
redo for SI units for closer to sg syllabus instead of arbitrary units originally made
22May2011
add earth picture
add panel of x,y,vx,vy,ax,ay for calculating values to coincident with Earth data
add trace instead of the older trail that can display older data
rotate newton's diagram by 5 degree to coincident with x=0, instead of the older 0.1*R
add time
change to acceleration instead of force
24 May 2011
add multiple representation of versus time and distance from center of earth    
add menu for circular motion R,2R,3R and escape velocity at theta 0,45,90
26 May 2011
minor changes on menu list name R_earth instead of 6.38E06 as suggested by leongster
made theta = blank
add check box on the bottom panel for quick access as suggested by leongster.
07 june2011
added reference frame space and earth for earth to rotate if frame is space
added a few geostationary orbits and non-geostationary
remove newton mountain and replace with a rectangle


to do
newton mountain gif to make background transparent


challenge:
[s]some problem detecting the boundary of earth[/s] solved

double hitEarth (double x, double y) {
 if (!pass) {
   return x*x+y*y-R*R;}
 else {
   return 0;}
}