In this lab, you can investigate the force exerted by one charged particle on another, and how that force varies with the distance between the particles (which can be varied). The graph shows the force exerted on the movable charge, which is the one on the right. A force to the right on the movable charge is shown as positive on the graph; a force to the left on the movable charge is shown as negative.

Using the buttons, you can plot the force vs. various functions of the distance.

What does it mean when the graph is a straight line?