Suction Cups Fight Back

1. Suction Cups Fight Back Materials: 2 large suction cups or Magdeburg-style hemispheres What you do: Press them together, then try to pull apart. What students see: They are surprisingly hard to separate. Question: What force is squeezing them together? 2. Crushing Can by Air Pressure Materials: Empty soda can; small hot-water amount; tongs; ice-water tray What you do: Heat a little water in can beforehand, invert into ice water. What students see: Can suddenly collapses. Question: Is the water pulling the can inward? 3. Cloud in a Bottle Materials: Clear plastic bottle; warm water; pressure pump/adapter What you do: Pressurize bottle, then release pressure quickly. What students see: A cloud suddenly forms. Question: Where was the cloud before we saw it?

Predict → observe three demonstrations → compare what changed → choose independent activity station → cleanup/share. Guiding questions: Question: What force is squeezing them together? Question: Is the water pulling the can inward? Question: Where was the cloud before we saw it?