The Double Pendulum With Elastic Rods Model shows two massless rods each with a different length. At the end of each rod is mass, m1; and m2. The user can vary the lengths of the rods and values of the masses within the simulation. A velocity dependent resistance can also be added by adjusting a drag variable in the simulation.  In this simulation, the rods are modeled as very stiff springs. If the rod gets longer or shorter than its rest length, a very strong force drives it back to its rest length. The spring constant for each rod is 1.0E+7 N/m. In a sense, this is what happens in a real double pendulum. A real physical rod pulls or pushes back to its rest length under tension or compression. There is also a drag force that is linearly dependent on the velocity vector. The drag constant determines the strength of the drag force. Initially the drag is set to zero.

The Double Pendulum With Elastic Rods Model was developed using the Easy Java Simulations (EJS) modeling tool.  It is distributed as a ready-to-run (compiled) Java archive.   Double clicking the jar file will run the program if Java is installed.  You can modify this simulation if you have EJS installed by right-clicking within the map and selecting "Open Ejs Model" from the pop-up menu item.

Please note that this resource requires at least version 1.6 of Java (JRE).