Science Projects And Inventions

YOU  NEED:

• A paper or plastic cup
• A sheet of paper
• A sharp pencil

A well known experiment can be switched around. The known experiment involves placing a sheet of paper over a glass which is half full of water. Then a palm is placed on top of the sheet of paper. The glass is turned upside down. The palm is removed carefully. You will observe that air pressure keeps the water from spilling out because the sheet is tightly pressed against the rim of the glass. The water pours out of the glass only at your bidding. The take off on this old experiment is a new one. Make a hole near the bottom of a plastic or paper cup. Repeat the Familiar experiment mentioned above over a basin or outdoors. Place your pointer finger on the hole to prevent air from entering above the water, and the paper will cling to the inverted glass.  You  can announce that on the count of three you can make the paper and the water to drop. Just remove your finger from the hole.

HOW DOES IT WORK?

A partial vacuum is created inside as long as the hole at the bottom of the glass remains covered. Outside air pressure keeps the sheet pressed to the rim of the glass. Once the hole is uncovered, the vacuum disappears, allowing outside air pressure to enter the glass and force both the sheet and the water to drop.