Question

How many spheres are rotating in the space shown below?

Hint:

When dealing with structure-from-motion animations, focus on the center and the boundaries of the motion fields. This helps distinguish overlapping structures rotating at different speeds.

Answer 1

Correct Answer: 2

Step 1: Read the motion.
Using the kinetic-depth effect, dots on one sphere share a common rotation axis and angular speed.
Step 2: Count the groups.
Cluster the dots into independent rotating sets; each set is one sphere.
\[ \boxed{\text{Number of independent rotating groups}} \]