In order to see the relationship of the electrostatic repelling force to the distance between the two balls, you will want to plot the x displacement of the hanging ball (proportional to the force for small angles!) relative to the distance between them.

To calculate the distance between two points on every frame, you will need to create a "distance" series.

• Choose Create->Distance

Edit Distance Dialog

• Select the two balls in the "Available Points" list and "Add >> " them to the "Ends of Distance" list.
• Click "OK".

This creates a series of data that displays the magnitude of the distance between the two points.