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'''Air pressure''' is the [[pressure]] we experience due to the [[weight]] of the [[atmosphere]]. The typical air pressure at [[sea level]] is one atmosphere (1 atm, or 760 millimeters of [[mercury]]); as you climb higher, the air pressure decreases. For example, the air pressure on top of [[Mount Everest]] is less than the air pressure on top of [[Denali]].

'''Air pressure''' is the [[pressure]] we experience due to the [[weight]] of the [[atmosphere]]. Since air is a fluid, this pressure takes the form of a force exerted uniformly, in all directions, against everything. The typical air pressure at [[sea level]] is one atmosphere (1 atm, 760 millimeters of [[mercury]], or 14.7 pounds per square inch).  Since the pressure is the result of all of the air above the observer, as one climbs higher, the fraction of the atmosphere that is above one decreases, so the air pressure decreases. For example, the air pressure on top of [[Mount Everest]] is less than the air pressure on top of [[Denali]], and 67% less than at sea level.

Air pressure is used by modern industry, in the form of pneumatic controls. Hydraulic controls are similar to pneumatic ones, but use fluid pressure instead of air pressure, and are more precise due to the less compressible quality of the fluids used.

Air pressure is used by modern industry, in the form of pneumatic controls. Hydraulic controls are similar to pneumatic ones, but use fluid pressure instead of air pressure, and are more precise due to the effectively incompressible quality of the fluids used.

A simple science experiment demonstrates the power of air pressure. Ask your parents for a few tablespoons of [[lemon]] juice or [[vinegar]], a few tablespoons of baking soda, and an empty milk jug or wine bottle (preferably with the cork still in). Pour the ingredients into the jug and quickly cap it. You will see the cap start to loosen, or the cork fly out, when the chemical reaction inside the container generates enough [[carbon dioxide]] to raise the air pressure inside the bottle above the air pressure outside. This is the same principle that airlines use to pressurize the inside of an [[airplane]]'s cabin. For an extra kick, ask your parents for a chunk of [[dry ice]] to put inside the milk jug. Dry ice, being made of [[solid]] carbon dioxide, greatly increases the air pressure when it "melts" into [[gas]]. Put the ice in the milk jug, quickly screw on the cap, and place the jug in a warm location to melt the dry ice. (The inside of an oven will do just fine... but be careful not to turn on the oven!)

There are a number of incredibly simple ways to demonstrate the pressure of air or other gases. One is to blow up a balloon. The pressure inside the balloon is ''greater'' than the outside air pressure, so it exerts an ''outward'' force, making the balloon expand. Other experiments, some safe and others less so, can involve mixing baking soda with a mild acid such as [[lemon]] juice or [[vinegar]]. But the simplest experiment, often done as a prank, is to shake a bottle or can of carbonated beverage. This causes the carbon dioxide to go out of solution.

==Biblical view==

==Biblical literalist view==

The [[Bible]] teaches us that before the [[Flood]], there was a "firmament", or vapor canopy, separating the waters of the [[heaven]]s from the waters of the [[earth]]. Because all that water was pressing down on the Earth's atmosphere, the air pressure in Biblical times would have been several times greater than it is today. Some [[creation scientist]]s credit the longevity of the [[patriarch]]s to the greatly increased air pressure — much as an [[astronaut]] living in a pressurized [[space station]] ages more slowly than his twin at home.

Some Biblical literalists believe that {{cquote|... before the [[Flood]], there was a "firmament", or vapor canopy, separating the waters of the [[heaven]]s from the waters of the [[earth]]. Because all that water was pressing down on the Earth's atmosphere, the air pressure in Biblical times would have been several times greater than it is today. Some [[creation scientist]]s credit the longevity of the [[patriarch]]s to the greatly increased air pressure — much as an [[astronaut]] living in a pressurized [[space station]] ages more slowly than his twin at home.}}  There are a few problems with this: There is no scientifically plausible mechanism that would cause the much denser water to lie above the air. There is no evidence suggesting that greater air pressure increases longevity. The pressure inside a spacecraft is not higher than normal. Also, the phrase "ages more slowly than his twin at home" suggests a confusion with the "[[Theory_of_relativity#The_Twin_Paradox|Twin Paradox]]" of relativity. The relativistic age difference is about 10 milliseconds per month.

[[Category:Physics]]

[[Category:Physics]]

[[Category:Meteorology]]

[[Category:Meteorology]]