Download ModelDownload SourceembedFeedback


Intro Page

Coulomb Pendulum Model

Two charges hanging from wires, repel each other. The simulation shows the motion and reports angle (from the vertical) for each charge. You can change the charge (in μC), initial position and damp the motion (set velocity equal to zero) of the charges. Users can examine the model if Ejs is installed. 


  1. For the same initial charge on each, push the v=0 button until the charges balance. What is the angle?
  2. If you increase the value of one charge, what difference do you expect in the angles where they will balance? Will it still be symmetric? Explain and then try it. 
  3. The charge is given in μC and the support string for each is 1m in length. Determine the mass of each (they have the same mass). 


  • Giancoli, Physics for Scientists and Engineers, 4th edition, Chapter 21 (2008).


The Coulomb Pendulum Model was created by Anne Cox and converted to JavaScript by Fremont Teng and Loo Kan Wee using the Easy Java Simulations (EJS) authoring and modeling tool.

You can examine and modify a compiled EJS model if you run the program by double clicking on the model's jar file.  Right-click within the running program and select "Open EJS Model" from the pop-up menu to copy the model's XML description into EJS.  You must, of course, have EJS installed on your computer. 

Information about EJS is available at: <> and in the OSP ComPADRE collection <>.

Joomla! Debug Console


For Teachers


Software Requirements


Android iOS Windows MacOS
with best with Chrome Chrome Chrome Chrome
support fullscreen? Yes. Chrome/Opera No. Firefox/ Sumsung Internet Not yet Yes Yes
cannot work on some mobile browser that don't understand JavaScript such as..... cannot work on Internet Explorer 9 and below


Joomla! Debug Console