Mouse Button Usage

-solar system simulator-

This applet simulates the movement of gravitationally interacting
particles. The initial configuration resembles an approximation  
of a solar system consisting of a sun and 3 planets.             
There are two operating modes: simulation and editing            
During simulation the particles are interacting and flying around
according to Newton's laws of motion.                            
A mouse click stops the simulation and switches the applet to    
editing mode. Here the user can add or remove particles as well  
as change their parameters: position, velocity and mass.         
This is all done with the mouse by clicking and dragging.        
(In order to change the mass of a particle the mouse has to have 
a middle mouse button.)                                          
A button labeled "Resume" switches back to simulation mode.      

Everything that leaves the screen is removed and thus stops      
interacting. So in order to remove a particle you'll just need   
to drag it outside the screen.                                   

The mass of a particle is represented by the size (radius) of    
it's circle on the screen.                                       
Beware, the mass scales cubic with the radius. ( m~r^3 )         
The velocities are shown in editing mode by lines starting at the
center of every particle. The line length is the approximate     
distance travelled by the particle in one second.                

note on speed and error:                                         
This applet is designed to work in real time always. It follows  
that simulation precision decreases when more particles are      
present. If particles come too close to each other computational 
errors become big and yield unrealistic behaviour.               
(particles fly apart at huge speed)                              

                                     - J.E. , March 2010