* Air: We can feel the wind, but the individual molecules of air are invisible in motion.

* Time: We can perceive the passage of time, but we can't actually see time moving.

* Thoughts: Our thoughts are constantly in motion, but we can't see them.

* The Earth: We don't feel it because we're moving with it, but the Earth is spinning and orbiting the sun.

Let me know if you'd like to try another riddle!