Air Pressure

The Basics of Air Pressure

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Air pressure, atmospheric pressure, or barometric pressure, is the pressure exerted over a surface by the weight of an air mass (and its molecules) above it. 

More: How high in the sky does air go?

How Heavy Is Air?

Air pressure is a difficult concept. How can something invisible ? Yet and still, air has mass because it is made up of a mixture of gases that have mass. Add up the weight of all these gases that compose dry air (Oxygen, Nitrogen, Carbon dioxide, Hydrogen, and others) and you get the weight of an air molecule.

 

The weight of dry air is has a molecular mass of is 28.97 units. While that isn't very much, when you think that a typical air mass is made up of -- air molecules, you can begin to see how .

So what's the connection between molecules and air pressure? If the number of air molecules above an area increases, there are more molecules to exert pressure on that area and its total atmospheric pressure increases. This is what we call "high pressure." Likewise, if there are less . -- also known as "low pressure."

Air pressure isn't uniform across the Earth. It ranges from 980 to 1050 millibars .

High Pressure

As of 2016, the highest pressure ever recorded on Earth is

Low Pressure

Lowest pressure in low pressure systems, hurricanes, .

As a general rule of thumb, lows have a pressure of around 1000 millibars (29.54 inches of mercury).

As of 2016, the lowest pressure ever recorded on Earth is 870 mb (25.69 inHg) in the eye of Typhoon Tip over the Pacific Ocean on October 12, 1979.

Air Pressure Basics

There are 5 basics about air pressure

  • It moves from high to low
  • how related to temperature?
  • how related to density?
  • Air pressure is measured with a weather instrument known as a barometer. (This is why it's also sometimes called "barometric pressure.")
  • It decreases as you travel up in . why?

     

    Atmospheric pressure is basically the weight of air in the atmosphere above the reservoir, so the level of mercury continues to change until the weight of mercury in the glass tube is exactly equal to the weight of air above the reservoir. Once the two have stopped moving and are balanced, the pressure is recorded by "reading" the value at the mercury's height in the vertical column.

    If the weight of mercury is less than the atmospheric pressure, the mercury level in the glass tube rises (high pressure). In areas of high pressure, air is sinking toward the surface of the earth more quickly than it can flow out to surrounding areas. Since the number of air molecules above the surface increases, there are more molecules to exert a force on that surface. With an increased weight of air above the reservoir, the mercury level rises to a higher level. If the weight of mercury is more than the atmospheric pressure, the mercury level falls (low pressure). In areas of low pressure, air is rising away from the surface of the earth more quickly than it can be replaced by air flowing in from surrounding areas. Since the number of air molecules above the area decreases, there are less molecules to exert a force on that surface. With a reduced weight of air above the reservoir, the mercury level drops to a lower level.

    Atmospheric pressure is basically the weight of air in the atmosphere above the reservoir, so the level of mercury continues to change until the weight of mercury in the glass tube is exactly equal to the weight of air above the reservoir. Once the two have stopped moving and are balanced, the pressure is recorded by "reading" the value at the mercury's height in the vertical column. If the weight of mercury is less than the atmospheric pressure, the mercury level in the glass tube rises (high pressure). In areas of high pressure, air is sinking toward the surface of the earth more quickly than it can flow out to surrounding areas. Since the number of air molecules above the surface increases, there are more molecules to exert a force on that surface. With an increased weight of air above the reservoir, the mercury level rises to a higher level.

    If the weight of mercury is more than the atmospheric pressure, the mercury level falls (low pressure). In areas of low pressure, air is rising away from the surface of the earth more quickly than it can be replaced by air flowing in from surrounding areas. Since the number of air molecules above the area decreases, there are less molecules to exert a force on that surface. With a reduced weight of air above the reservoir, the mercury level drops to a lower level. Atmospheric pressure is basically the weight of air in the atmosphere above the reservoir, so the level of mercury continues to change until the weight of mercury in the glass tube is exactly equal to the weight of air above the reservoir. Once the two have stopped moving and are balanced, the pressure is recorded by "reading" the value at the mercury's height in the vertical column. If the weight of mercury is less than the atmospheric pressure, the mercury level in the glass tube rises (high pressure). In areas of high pressure, air is sinking toward the surface of the earth more quickly than it can flow out to surrounding areas. Since the number of air molecules above the surface increases, there are more molecules to exert a force on that surface. With an increased weight of air above the reservoir, the mercury level rises to a higher level.

    Since the number of air molecules above the area decreases, there are less molecules to exert a force on that surface. With a reduced weight of air above the reservoir, the mercury level drops to a lower level.

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    Means, Tiffany. "Air Pressure." ThoughtCo, Jan. 1, 2017, thoughtco.com/air-pressure-basics-4019644. Means, Tiffany. (2017, January 1). Air Pressure. Retrieved from https://www.thoughtco.com/air-pressure-basics-4019644 Means, Tiffany. "Air Pressure." ThoughtCo. https://www.thoughtco.com/air-pressure-basics-4019644 (accessed September 21, 2017).