Our model scenario is shown in the image below. It consists of two springs connected end-to-end, with one end of the joined springs attached to the ceiling and the other end attached to a hanging mass. The top spring (modeling the stretchy bond) has a spring constant of 3k, and the bottom spring (modeling the molecule) has a spring constant of k. The hanging mass (representing the AFM tip that applies the force to the molecule) is m. The springs themselves do not have any mass. The whole system is at rest, and the gravitational field is the usual g = 9.8 N/kg. m 3k 32 K