How can the liquid rise upwards along the walls of the tank?.?

Question

When a liquid is spung within a cylindrical vessel,the level of the liquid does not remain horizontal, but it rises up along sides of the walls of the cylinder. For spinning we give only a horizontal angular force to the liquid. But how can the liquid rise up like that without any vertical force applied or generated?.

Answer 1

It's the same reason as why water spreads out when only under the vertical gravitational force, namely that this is the natural equilibrium shape of minimum potential energy. The liquid assumes a level consistent with the local acceleration, which is the sum of gravity and radial acceleration given by w^2*r, where w is the rotational rate in rad/sec and r is the radius. The resulting surface is a paraboloid, and it is perpendicular to the acceleration at all points.