<I>Comment on</I>: Curling rock dynamics - The motion of a curling rock: inertial vs. noninertial reference frames

Abstract

We examine the approach used and the results presented in a recent publication (Can. J. Phys. 76, 295 (1998)) in which (i) a noninertial reference frame is used to examine the motion of a curling rock, and (ii) the lateral motion of a curling rock is attributed to left-right asymmetry in the force acting on the rock. We point out the important differences between describing the motion in an inertial frame as opposed to a noninertial frame. We show that a force exhibiting left-right asymmetry in an inertial frame cannot explain the lateral motion of a curling rock. We also examine, as was apparently done in the recent publication, an effective force that has left-right asymmetry in a noninertial, rotating frame. We show that such a force is not left-right asymmetric in an inertial frame, and that any lateral motion of a curling rock attributed to the effective force in the noninertial frame is actually due to a real force, in an inertial frame, which has a net nonzero component transverse to the velocity of the center of mass. We inquire as to the physical basis for the transverse component of this real force. We also examine the motion of a rotating cylinder sliding over a smooth surface for which there is no melting: we show that the motion is easily analyzed in an inertial frame and that there is little to be gained by considering a rotating frame. We relate the results for this simple case to the more involved problem of the motion of a curling rock: we find that the motion of curling rocks is best studied in inertial frames. Perhaps most importantly, we show that the approach taken and the results presented in the recent publication lead to predicted motionsof curling rocks that are in disagreement with observed motionsof real curling rocks.