Double Pendulum

The Falling Smokestack Problem

Have you ever seen a falling smokestack? First, several bricks a broken off from one side at its bottom. Then, the resulting cavity is filled with explosive that is subsequently set off. After that the smokestack tilts a little bit and finally it falls down. If it is short and thick, it falls like a tree -- see fig a). But if it is long and thin, it breaks during its fall. The question is: Which figure, b) or c) shows correctly how the smokestack breaks as it falls?


  1. There is a 3d model of a double pendulum above. Use this model to help you guess the right answer to the falling smokestack question. Describe how you used the model.

  2. Once you know how the smokestack breaks as it falls, a fair a question is, why does it break as it does? Can you explain why the double pendulum (or smokestack) fall in this particular way?

The applet above uses Open Source Physics library developed by Dr. Wolfgang Christian et. al. at Davidson College. It's source code is published here under the GNU GPL licence without any guarantee. For the details, please see the text of the licence.

Written by Slavomir Tuleja, August 2003.