You can click on the "Add Mass" button, click the mouse out in the white area and get some fine little round objects; try two or three to start. Then click on "Add Stiff Spring"; click and drag from one object to then next to get springs attached. Then click on "Pull Mass". Now you can drag each object to stretch the springs; don't stretch too much for starters. Now click on "Start" and watch the springs push and pull the masses around.

After you become bored you can "Stop" and "Clear" to get begin a fresh assembly. You can add softer springs with the "Add Soft Spring" button. (The stiff springs have a spring constant 10 times the spring constant of the soft springs.)

If you place a number of objects in a line and connect them by springs and pull, once you start you notice that they gradually move to a clump. This happens because the line of a given spring can easily pivot about the point where the spring is connected to the object. You can see some of the effects which occur when springs are in a line by clicking the "change to 1D" button. Now when you place the objects and springs, they will be placed in a one dimensional line; their subsequent motion is confined to that line.

Some of you will immediately recognize that with two sorts of springs you can build two seperate spring oscillators (of stiff springs) weakly coupled by a soft spring in one dimension. Excite one oscillator and after a while the energy will be transfered to the other oscillator.

You can return to two dimensional motion by clicking the "change to 2D" button.

This applet is written in JAVA. I got the idea from a masses and springs applet written by Dennis C Rapaport, Department of Physics, Bar-Ilan University, Ramat-Gan, Israel. I wrote my own version.