The Free Fall 3D model is  a designed to teach Ejs modeling.  Right click within the simulation to examine this model in the Ejs modeling and authoring tool.  See:
"Modeling Physics with Easy Java Simulations" by Wolfgang Christian and Francisco Esquembre, The Physics Teacher, November 2007, 45 (8), pp. 475-480.
The Easy Java Simulations (EJS) manual can be downloaded from the ComPADRE Open Source Physics collection and from the Ejs website.
This simulation was created by Wolfgang Christian using the Easy Java Simulations (Ejs) modeling tool. You can examine and modify this simulation if you have Ejs installed by right-clicking within a plot and selecting "Open Ejs Model" from the pop-up menu.
Information about Ejs is available at: .

3D Navigation
The model's 3D view has many built in features that can be accessed as the program is running.
Left-button click-dragging on the particle changes its position.
Left-button click-dragging on an empty regions rotates the view.
Left-button shift-click-dragging zooms in and out.
Left-button control-click-dragging translates (pans) the view.
Left-button alt-click-dragging displays a 3D cursor on the scene (if the panel is “Enabled”).
It the ‘x’, ‘y’ or ‘z’ key is pressed during a mouse action, the actions affects only this coordinate.  Note also that these actions are are modified if the 3D view is projected onto a 2D plane.
Right-clicking within a 3D view displays a popup menu as shown below.

[b][color=blue]My input/contributions are
1. Event for ODE Evol Page is not working to my satisfaction but the codes is
[code]if(vz>0) return 1;  // particle is not falling
//if (z>0) return 1;  // if particle z is greater than 0 , do nothing
return z-0.0; // change 0.0 to 0.5 for z =0.5 to action[/code]
[s]note: the if z>0>) return 1; the number 0 cannot be changed to a positive number but works for negative ??[/s]

2. panel on left[/color][/b]

[color=red][b]source code
download the *.jar for using the applet on standalone without internet connection.[/b][/color]