Ace Your Chemistry Science Project by Robert Gardner

Author:Robert Gardner [, ]
Language: eng
Format: epub
ISBN: 978-1-4645-0501-0
Publisher: Enslow Publishers, Inc.
Published: 2010-03-14T16:00:00+00:00

AIR PRESSURE EFFECTS EXPLAINED

Air pressure can support a column of mercury 76 cm (30 in) high and a column of water 10 m (34 ft) tall, so it is not surprising that it can support a column of water in a bottle as it did in “The Amazing Upside-Down Bottle of Water.” When the water in the drinking-straw pipette (in “A Drinking-Straw Pipette”) starts to fall out of the straw, it slightly lengthens the air column below your finger. Because the volume of air above the water in the straw has grown slightly larger without any new air entering the straw, that air now exerts less pressure than the air below the water in the straw. Because the air pressure above the column of water in the straw is less than the air pressure around it, the water stays in the straw pipette. As soon as you remove your finger, air enters the top of the straw. This makes the air pressure above the water the same as the air pressure beneath it. The water’s weight then causes it to fall. The same explanation applies to “Two Ways to Prevent a Can from Leaking.” As water leaks from the covered can, the volume of air trapped above the water increases. This expansion reduces the air pressure in the can. When the sum of the pressures exerted by the air above the liquid and the liquid itself equals the air pressure outside the can, the water stops flowing.

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