<P> If a liquid is contained in a cylindrical vessel and is rotating around a vertical axis coinciding with the axis of the cylinder , the free surface will assume a parabolic surface of revolution known as a paraboloid . The free surface at each point is at a right angle to the force acting at it , which is the resultant of the force of gravity and the centrifugal force from the motion of each point in a circle . Since the main mirror in a telescope must be parabolic , this principle is used to create liquid mirror telescopes . </P>
<P> If a liquid is contained in a cylindrical vessel and is rotating around a vertical axis coinciding with the axis of the cylinder , the free surface will assume a parabolic surface of revolution known as a paraboloid . The free surface at each point is at a right angle to the force acting at it , which is the resultant of the force of gravity and the centrifugal force from the motion of each point in a circle . Since the main mirror in a telescope must be parabolic , this principle is used to create liquid mirror telescopes . </P>
the free surface of a rotating fluid is
the free surface of a rotating fluid is
a paraboloid
a paraboloid