[SOLVED] spinning liquid creating a parabolic shape take a container of liquid and spin it... a parcel at any given radius (r) experiences (in the rotating frame) a force outward = mass x angular speed^2 x r and a vertical force of mg. Thus the surface curves such that the tangent to the surface makes an angle to the horizontal given by tan theta = angular speed^2 x r/g. two questions: -I think this is simple and I'm just missing it... how do I prove that the resultant shape is a parabola? -what provides the force we see at work? surface tension? pressure gradient? Basically how do we draw a free body diagram for the parcel of liquid in the Earth frame? Thank you!