Cup, Card and Water Trick

Thu, Jan 5, 2012

Materials: Index card, plastic cup, water

Activity: Fill a plastic cup one-half full of water. Put an index card on top of the cup. While holding the card tightly against the mouth of the cup, turn the cup upside down. Gently let go of the card. The water stays in the cup! The air pressure pushing up on the index card is greater than the pressure inside the cup.

Research Questions: What happens if you tip the cup? What happens if you use more or less water? What happens if you poke a hole in the bottom of the cup, and keep the hole covered until you have flipped the cup over? What happens if you poke a hole in the index card, and keep the hole covered until you have flipped the cup over? How does the size and shape of the cup affect the result?

Resources:

Index Card, Cup and Water Trick

Air has Weight

Tags: Liquid Air Pressure 2012