Pressure in Action!

Let's talk about air pressure. What is air pressure? To learn about air pressure, we must first define what pressure is. Pressure is the effect that occurs when a force is applied to a surface. P equals F divided by A. The force of air is caused when particles in the air being pulled toward the center of the Earth by gravity. Since air is made of "stuff," it has mass and weight. Therefore it creates a pressure due to gravity pulling the "stuff" toward the center of the Earth.

Picture a clear plastic tube going from a spot on Earth to 600 miles above sea level. That is where the atmosphere ends. In other words, there is no more "stuff." Now let's fill the tube with eggs. The eggs at the bottom of the tube will have greater pressure on them causing them to break and become more dense as the eggs now fill all the space in the bottom of the tube. The eggs at the top of the tube have less pressure on them because there are fewer eggs above them. With that picture in mind, you should be able to get an idea of air pressure. The farther on Earth's surface you stand, as on Mount Everest, the fewer eggs above you, and the less pressure. The closer to the center of the Earth, as in the Sea of Galilee, the more eggs above you and the greater the pressure.

We can measure the air pressure using different instruments. We have manometers and barometers. The barometers can be mercury barometers or aneroid barometers. An altimeter is bascially an aneroid barometer.

One of the most interesting places in the United States at sea level, is Key West, Florida. The elevation of Kest West is sea level to a whopping 18 feet above sea level at Solaris Hill. Air pressure on a standard day at Key West is measured at 29.92 inches of mercury or 760 milimeters of mercury or 1013.25 milibars.

On top of Mount Everest in the Himalayan Mountains, the altitude is 29,028 feet. That is about five-and-a-half miles high. The air pressure is so low that the people who usually climb Everest usually need to have extra oxygen with them (Whoo, I could use that myself!). Once again, you have a lower pressure at sea level because there are fewer air particles above.

The highest point in the State of Georgia is a mountain peak called Brasstown Bald. The eleveation is 4,784 feet. Remember, you have a lower pressure than sea level because there are fewer air particles above.

Reducing our altitude below sea level, we travel to the Salton Sea in California. The altitude is 228 feet BELOW sea level, and since we are below sea level, we have more particles of air stacked above us, hence greater pressure. More "stuff" means more weight and a greater force.

Finally, we are at Lake Kinneret, the Sea of Galilee in Israel. Lake Kinneret is the lowest freshwater lake on Earth and located in the Great Rift Valley. The elevation of the lake is 696 feet BELOW sea level. Because there is more "stuff" above us, like at the Salton Sea, the pressure is greater.

Now that you know the elevations of these locations, use the air pressure versus altitude chart to determine the approximate air pressure on a standard day for each location.