is the rotational direction, i.e. direction parallel to the surface is the tangential velocity, i.e. velocity parallel to the surface is the planar direction, i.e. direction normal to the surface is the normal velocity, i.e. velocity normal to the surface is the radius.
is the rotational direction ie direction parallel to the surface is the tangential velocity ie velocity parallel to the surface is the planar direction ie direction normal to the surface is the normal velocity ie velocity normal to the surface is the radius