The Einstein Cannon model computes and displays the trajectory of cannonballs (particles) shot from a cannon in the vicinity of a black hole.  It was created for the study of Einstein's theory of general relativity and the Schwarzschild metric.  The main window displays a map of space in the vicinity of the black hole using Schwarzschild coordinates and a cannon located a distance r0 from the center black hole's center.  The position and firing angle of the cannon can be adjusted by dragging a marker and the number of cannon balls and their initial speed can be changed using input fields.  The maximum speed of the cannon ball is the speed of light c=1 in accordance with Einstein's theory.  Newton suggested that a cannon ball fired from a high mountain could fall to Earth, orbit the Earth, or fly away depending on how it was fired.  The same is true in general relativity but there are many important differences.  This model demonstrates these differences.

The Einstein Cannon model is a supplemental simulation for the article "When action is not least for orbits in general relativity" by C. G. Gray and Eric Poisson in the American Journal of Physics 79(1), 43-55 (2011) and has been approved by the authors and the American Journal of Physics (AJP) editor.  The simulation was developed using the Easy Java Simulations (EJS) modeling tool and is distributed as a ready-to-run (compiled) Java archive.  Double clicking the ejs_gr_EinsteinCannon.jar file will run the program if Java is installed.

Please note that this resource requires at least version 1.5 of Java.