Suction Cups Fight Back
They are surprisingly hard to separate.
Teaching & key ideas
What you do: Press them together, then try to pull apart.
What students see: They are surprisingly hard to separate.
Why it works: Removing air lowers pressure inside; outside atmospheric pressure pushes them together.
Question to ask: What force is squeezing them together?
Lesson flow
Predict → demonstrate → observe → briefly explain → ask: What force is squeezing them together?