Cup and Card

Objectives

• Explain how air pressure works

Materials

• Cup or Jar (with ring lid)

• Square or circle of hard thin plastic (a yogurt tub lid, for example) or cue card (thick paper)

• Jug of water

• Square of window screen or mesh (for Part 2)

Key Questions

• How does the water stay in the jar?
• Part 2: What direction does the air move when you tap the jar? Why?

What To Do

Part 1:

1. Pour water into the cup
2. Hold a piece of plastic over the mouth of the jar
3. Quickly flip the cup over so the cup is upside down
4. Remove your hand from under the plastic!

Part 2:

1. Cover the mouth of the jar with a piece of screen and use the ring lid to keep it taught and in place
2. Repeat steps 2 and 3 above
3. Remove your hand from under the plastic.
4. Without wiggling or tipping the jar, remove the plastic entirely!
5. Holding the jar over the jug of water, tap the jar to observe what happens.