Using a few items from around the house you can prove air pressure exerts a force in all directions. According to "Science Guy" Jason Lindsey with Hooked on Science, you can use this scientific knowledge to play a fun science trick on the family.
* Transparent cup
* Index card
STEP 1: Fill the transparent cup with water.
STEP 2: Place the index card over the mouth of the transparent cup.
STEP 3: Hold the index card in place, slowly turn the transparent cup upside down, and then remove your hand from the index card. What happens?
The index card stays in place because air pressure is pushing up against the index card. The pressure pushing up is more than the weight of the water pushing down from the inside of the transparent cup, therefore the index card stays in place.
Jason Lindsey is a Science Outreach Educator with Hooked on Science. Check out his website "Hooked On Science" at hookedonscience.org for webcasts and experiments that might get you hooked on science. Send him your science questions at email@example.com. More science experiments can be found at www.semissourian.com.