The animation shows the discharge of a capacitor. By using the slider you can change the value of the resistor through which the capacitor discharges (100 Ω or 200 Ω). It is best to do this before running the animation.
The current (I) in the discharge at an instant is:
I = - dq/dt
But V = IR and q = CV so dq/dt = d(CV)/dt = C dV/dt
Therefore we have V = -CR dV/dt
Rearranging and integrating gives: