1. The problem statement, all variables and given/known data A box of mass m is set on a merry-go-round of radius r with a linear speed v. The friction coefficient between surfaces is μ. 2. Relevant equations ac = v²/r 3. The attempt at a solution I imagined this problem because I'm trying to understand more deeply circular motions. I have many ideas (more questions maybe, tell me cause I'm probably wrong) such as : the merry-go-round is trying to set the box in motion, so the friction force is pushing the box in the opposite direction. The problem is I don't understand the action of centripetal acceleration in this case even if I place myself in the turning frame. I know the circular motion is a state that requires an acceleration perpendicular to the speed in order to make only change its direction but I don't really understand what's going on here.