In physics, circular motion is a motion of an object along the circumference of a circle and is rotation along a circular path or a circular orbit. It can be uniform, that is, with constant angular rate of rotation (and thus constant speed), or non-uniform, that is, with a changing rate of rotation. The rotation around a fixed axis of a three-dimensional body involves circular motion of its parts. The equations describing circular motion of an object do not take size or geometry into account, rather, the motion of a point mass in a plane is assumed. In practice, the center of mass of a body can be considered to undergo circular motion.