A particle on top of a smooth sphere is given an initial horizontal velocity. At what point does it lose contact with the surface of the sphere? In this video I solve this classic dynamics problem. Follow-up video (including rotation and moment of inertia) here: About me: I studied Physics at the University of Cambridge, then stayed on to get a PhD in Astronomy. During my PhD, I also spent four years teaching Physics undergraduates at the university. My website: #physics #maths #math #mechanics #dynamics #forces #resolving #particle #smooth #sphere #motion #circularmotion