2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/174119We took three lawn tennis balls arbitrarily. One was moderately old, one was old and another was new. Fabricating a conveyor belt set-up we have measured rolling friction coefficients, $μ_{r}$, of the three balls as a function of their angular velocities, $ω_{ball}$. In all the three cases, plotting the results and using linear fits, we have obtained relations of the form $μ_{r}= k_{rol} ω_{ball}$ and have deduced the proportionality constant $k_{rol}$. Moreover, core of a lawn tennis ball is made of vulcanised India-rubber. Using the known values of Young modulus and shear viscosity of vulcanised India-rubbers in the theoretical formula for $k_{rol}$, we estimate $k_{rol}$s for the cores made of vulcanised India-rubbers, assuming Trouton ratio as three. The experimental results for the balls and the semi-theoretical estimates for the cores, of $k_{rol}$, are of the same order of magnitudes.9 pages, 6 figuresClassical Physicstext