In physics, the concept of absolute rotation—rotation independent of any external reference—is a topic of debate about relativity, cosmology, and the nature of physical laws.
Figure 1: The interface of two immiscible liquids of different density (a denser colorless liquid and a lighter orange-colored liquid) rotating around a vertical axis is an upward-opening circular paraboloid.
Rotation or rotational motion is the circular movement of an object around a central line, known as axis of rotation. A plane figure can rotate in either a clockwise or counterclockwise sense around a perpendicular axis intersecting anywhere inside or outside the figure at a center of rotation. A solid figure has an infinite number of possible axes and angles of rotation, including chaotic rotation, in contrast to rotation around a fixed axis.
Star trails caused by the Earth's rotation during the camera's long exposure time