Fig 3. Shear stresses along the walls during one period on the RPM.

Both frames rotate with constant and equal velocity; the flask is placed at the center of rotation. The rotational velocity is 60 deg/s. The time interval between the illustrations is 1 second (top left: 0 s; top middle: 1 s; top right: 2 s; bottom left: 3 s; bottom middle: 4 s; bottom right: 5 s).