Suction Cups Fight Back

They are surprisingly hard to separate. Ask students to predict what will happen. Press them together, then try to pull apart. Key idea: Removing air lowers pressure inside; outside atmospheric pressure pushes them together. Ask: What force is squeezing them together? Safety and cleanup: Use handles; no sudden release near faces. https://www.physics.purdue.edu/demos/display_page.php?item=2A-01