Are rotational motion and circular motion different or the same? If different then when can we say that a body is in circular motion, and when it's in rotational motion? I find several answers where it is stated that in circular motion, the axis of rotation is inside the body, while the axis of rotation in the other case, may be outside. Why is the axis outside in the case of rotational motion?
[Physics] Difference between circular motion and rotational motion
orbital-motionrotational-kinematicsterminology
Best Answer
Maybe a better distinction to make would be between rotational motion and orbital motion. Even in that more generalized case (orbital could be something other than circular), the properties used to describe and analyze the motions are the same: axis of motion, angular momentum, moment of inertia, kinetic energy, torque, etc.
There is not a bold line of difference between the two, but generally, rotational motion refers to objects which are extended (not points) and spin about an axis which either within the material of the object or is not farther from the center of mass than the farthest dimension of the object.
Orbital (or "circular") refers to the motion of an object, which may or may not be spinning around an internal axis, around some point far from its center of mass and either repeats a path or nearly repeats a path (e.g., Mercury). More generally, the path doesn't even need to repeat because there are open orbital paths which astronomical objects routinely take.
One could say that rotational motion of a solid object is the orbital motion of thousands of particles, all moving about the same axis with the same angular frequency.
Don't get concerned about the distinction between rotational and orbital; it's not hard and fast. But you should be careful about using circular because that is very specific.