A correction for spring mass in the ubiquitous centripetal force experiment of freshman physics Available to Purchase

A widely deployed experiment in freshman physics tests the hypothesis that the magnitude of the central force that accomplishes uniform circular motion is mv²/r (equivalently mrω²). This is accomplished by using a spring rotating about one end as the central force applied to a vertically hanging bob of known mass, tracking a circle of measured radius, at a speed deduced by counting revolutions over time. The spring force is independently measured by determining the gravitational force that produces the same degree of extension of the spring. Because the inertia of the spring is unimportant to the latter measurement, but does matter in the dynamical phase of the experiment, an error is introduced. Students have always been admonished to neglect the effects of the mass of the spring; however, typical parameters used in this experiment imply an error greater than 1%, which exceeds the probable error of which the experiment is capable.