In this display we have replaced the position variable which we called "p" in the pendulum discussion with the more common "x". In the Duffing Oscillator displays, "x" represents the displacement of the center of the flexing strip. The velocity "V" of the pendulum display is now represented by the symbol x'. The ' symbol added to a variable name means the rate of change of that variable with respect to time, or "derivative" with respect to time. See the Physics 1 - Mechanics program for more on rates of change and derivatives.
In the various views of this display, some information has been added in the bottom border. The equations for the forces acting on the system are summed up and displayed as Total Force. The three terms in the total Force are the applied force, the restoring force and the drag force. The effective mass of the system is hidden in the coefficients of the force terms, the 15, 1 and 1 in this example. The time dependence of the forcing function is cos(*t+) where is the "angular frequency" of the magnet current and is its "phase angle". Angular frequency may be thought of as just a time scale factor so we can adjust forcing function cycle time. Phase angle is just a term to allow us to adjust the forcing functions starting value at time = 0. In this example =1 and =0. The restoring force is proportional to the third power (cube) of displacement, x, and the drag force is proportional to the velocity, x'. Also appearing in the bottom border is the initial state of the system, shown as an ordered pair (x,x') in IC=(0,0).