Paper Won't Enter the Bottle
The ball often pops back toward you instead of going in.
Teaching & key ideas
What you do: Place the ball at the mouth and blow straight into the bottle.
What students see: The ball often pops back toward you instead of going in.
Why it works: Air already inside the bottle must escape and pushes back.
Question to ask: Why can't the paper simply move into the bottle?
Lesson flow
Predict → demonstrate → observe → briefly explain → ask: Why can't the paper simply move into the bottle?