“Air Versus Water,” Friend, Jan. 1991, 5
To see that air pressure can be stronger than water pressure, you will need: a paper cup, paper, and water. (This experiment should be done over a sink or outdoors.)
Fill the cup 3/4 full of water.
Place the paper over the cup, and press it in place with your hand for 30 seconds.
Still holding the paper in place, slowly turn the cup upside down. Lower your hand from the paper. Because it is stronger than the weight (pressure) of the water, the air pressure under the cup will hold up the paper and the water in the cup.