Translation and rotation are aimed at rigid bodies, so the distance between any two points remains the same when the object moves and will not be its mirror image. The motion of a point can always be regarded as translation.

Translation is the movement in which the direction and distance between any two points on the object are constant from one point to another when the object is moving!

Translation can also be defined as: when an object moves, every point on the object is in the same movement.

The latter definition is not very good: different initial positions are regarded as "the same motion situation", but the trajectory has the same shape and size, but it is not necessarily "the same motion situation". For example, a circle rotates around the center of the circle, and the trajectory of each point is the same shape and size.

Rotation is the movement that the distance between each point and the same point (which can be outside the object) is constant when the object moves, which is called rotation around this point, and this point is called the rotation center of the object. So, it doesn't have to be around an axis.

I remember a sentence in my high school book called "both translation and rotation". I want to clarify that "both translation and rotation" is usually "neither rotation nor translation", but it can be regarded as the superposition of the two movements.

When I say "usually", I mean that rotation around one point can be regarded as the result of rotation around another point plus a translation! Especially when the center of rotation is outside the object, it is often considered as "both translation and rotation". At this time, this movement is "rotation, not translation".

There is also a common situation that an object is regarded as rotating around the center of mass (or geometric center), that is to say, the center of rotation is often taken at the center of mass or geometric center of the object. If the center of mass (or geometric center) moves, it is called "translation", regardless of whether it can be regarded as an object moving around another point.

Is Teacher No.24 wrong?