Modeling molecular motors, the two-state model. Interaction potentials as a function of space; (A) The particle is trapped in the minimum of interaction potential (1). When the particle is in the excited state, it undergoes a non-restricted Brownian motion and it diffuses (B); the distribution of positions is shown. When the ground state is applied again (C), more particles go to the left (3) than to the right (2). UG: interaction potential of the ground state; UE: interaction potential of the excited state.