Experiment of December 9, 2025:

The time to submit an answer is over. You can now view the solution of the experiment.

Solution video:

Experiment:

Question:

What does Mr. Santa observe?

A) He sees the black stripe shifted upwards.

B) He sees the black stripe move downwards.

C) He sees the black stripe unchanged.

D) The black stripe is no longer visible; it seems to have disappeared.