Arrow Reverses Through Water
Arrow appears to reverse direction.
Teaching & key ideas
What you do: View arrow through empty then water-filled cylinder.
What students see: Arrow appears to reverse direction.
Why it works: The curved water-filled container acts like a cylindrical lens; rays cross.
Question to ask: Did the arrow turn around?
Lesson flow
Predict → demonstrate → observe → briefly explain → ask: Did the arrow turn around?