When a container of water is at rest (in an inertial reference frame) the surface of the water is flat (horizontal). However, when the container of water is placed on a rotating platform and spun at a constant angular velocity, the water height forms the shape of a parabola due to the centrifugal force in the rotating (non-inertial) reference frame.
The observation of this effect was instrumental in encouraging Sir Isaac Newton to develop his laws of motion for inertial reference frames.
This is also the way that large parabolic mirrors are constructed today: molten glass is heated to the melting point in a furnace while the glass is rotating a constant angular velocity.
