Roll-Back Can
It slows, stops, and rolls back by itself.
Teaching & key ideas
What you do: Roll it away across the floor/table and let go.
What students see: It slows, stops, and rolls back by itself.
Why it works: A hidden weight twists a rubber band, storing energy that later unwinds.
Question to ask: Where did the can get the energy to come back?
Lesson flow
Predict → demonstrate → observe → briefly explain → ask: Where did the can get the energy to come back?