Air Pressure - Index Card

INTRODUCTION

Air is all around us and it exerts pressure in all directions. This experiment will show the exertion of air pressure on the index card.

MATERIALS

• Small, transparent plastic cup
• 4" x 6" index card
• Water

WHAT TO DO

1. Fill a cup ½ - ¾ full with water.
2. Wet the lip of the glass with water and place the index card on top of the cup.
3. While holding the index card in place with one hand, use the other hand to flip the cup upside down.
4. Continue to hold the cup upside down and remove your hand from the index card. What happens?
5. To flip the cup right side up, hold the index card to the cup and quickly flip the cup.

QUESTIONS

1. When the cup is upside down what is pushing on the card? What is pushing on the card from above? From below?
2. Explain why the index card does not fall off.

SUMMARY

The pressure applied to the index card by the water is less than the pressure applied by the air. In other words, the air is pushing up on the card more than the water is pushing down on it. Therefore, the air pressure is holding the paper snug against the cup.

SOURCE

"Science Is." Susan V. Bosak, Scholastic Press, 1991. ISBN 0-590-74070-9

© S. Olesik, WOW Project, Ohio State University, 1999.