press the flag to make it draw a bunch of field lines. I couldn't be bothered to figure out how to determine where to draw lines and how many so it just draws a bunch of em around each object. press space to clear all lines click to draw a field line that goes through the position of your mouse cursor. edit the values of the x, y, and Q list to change the objects. x and y are for position, Q is for electrical charge. also this doesn't draw arrows on the field lines. Nor does it draw non-charged objects. also it will probably hang if you click on a position with Fel = 0. It works fine when it encounters such a position while drawing though, just not if it starts drawing on one.
basically it just calculates the force vector at a given point, then draws a tiny line segment on that point in the direction of the vector and repeats that process until it either hits an object or hits the edge of the screen. For the lines where you click it will do one pass in the positive direction and one in the negative direction.
