What is measured by the axis of rotation?

The axis of rotation refers to an imaginary line around which an object rotates. This concept is fundamental in understanding rotational motion, as it defines the central line that serves as the pivot point for that motion. When an object spins or rotates, every point in the object moves around this axis in a circular path. For example, in a spinning top, the axis is the line that passes through its tip around which it rotates.

The other options, while related to motion, do not accurately define the concept of the axis of rotation. The direction of force application relates to how forces affect an object's movement, the distance moved by an object measures linear displacement, and the speed at which an object rotates pertains to the rate of rotational movement rather than the central line itself. Thus, recognizing that the axis of rotation is about the central line around which motion occurs provides a clear understanding of its significance in physics and biomechanics.