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Learning Lesson: Measure the Pressure - The "Wet" Barometer

OBJECTIVE | Make your own barometer. |
OVERVIEW | Using simple items the student will make a device for indicating air pressurechanges, called a barometer. |
TOTAL TIME | Construction time 5 minutes.
Observation time 10 days. |
SUPPLIES | Glass or beaker with straight sides
Plastic ruler
Tape
One foot of clear plastictubing
Molding clay or chewing gum
Water
Food coloring |
PRINTED/AV MATERIAL | None |
TEACHER PREPARATION | None |
SAFETY FOCUS | Thunderstorm safety |

Background
The amount of air over us isconstantly changing. As a result, the weight of that air, called pressure, is constantly changing. These changes in air pressure are indications of changes in our weather. We measure this changeusing a device called barometer (bar-meter or measurer).

This first barometer was created by Evangelista Torricelli in 1643. Torricelli was actually trying to discover the reason that water would riseno more than 33 feet up a tube though the use of a suction pump. He had first built a water barometer, but it required a glass tube 60 feet long. Aware that mercury was 14 times heavier than water, heconstructed a tube only 35 inches long. Filing the tube with mercury and inverting the tube into a bowl of mercury caused mercury in the tube to drop to a level around 30 inches and creating a vacuumat the top of the tube.

The top of the mercury column was observed to fluctuate by a few percent, due mainly to what we now know to be fluctuations in atmospheric pressure. This is because as thecolumn of air directly above the barometer pushes on a dish containing mercury, it is forced up a tube. The stronger the downward push, the higher the pressure and therefore the higher the mercuryrises in the tube. This is where the unit "Inches of Mercury" comes from.
Procedure
1. Place the ruler in the glass and tape it to one side. (Make sure the numbers are visible.)
2. Tape the...
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