# How can I calculate magnetic field strength of a variable gap magnet?

I am currently doing an experiment where an aluminium pendulum is passed through a variable gap magnet (creating eddy currents). The variable I am changing is distance between the two grade N35 neodymium magnets. My hypothesis I am trying to prove is "If the distance between the magnets increases, then the magnetic field strength decreases in an inverse square relationship, thus causing less electromagnetic braking to occur on the pendulum"

I was wondering how to go about calculating the magnetic field strength of such a variable gap magnet. Currently, I have found the following equations to relate force to magnetic field. https://gyazo.com/1b4ec590440532b25dd60fbcd7e02eb2 https://gyazo.com/4eecc4baba1428082433b3cc43e2f55b

However, I am confused as to what qm1 and qm2 relate to, and am also not sure how the second equation is used in terms of the velocity value, as in this context the velocity value is constantly changing for the pendulum as it is swinging through and creating a harmonic motion.

I have done the trials/data already and have calculated the damping coefficients through the desmos, if they happen to be needed. Thank you so much for any help!