Comment on ‘Sliding down over a horizontally moving semi-sphere’

Abstract In a recent paper (2022 Eur. J. Phys. 43 035 004) Lineros considers a block (not necessarily initially at rest) which slides down from the top of a frictionless horizontal movable semi-sphere. The author studies the angle at which the block loses contact with the sphere and derives a cubic equation which determines that angle. In this comment, a considerably more elementary derivation of that result is presented.