We are confronted with it every day with the weather forecast; air pressure. The pressure is the pressure a column of air exerts on its surroundings. It is involved in a number of daily activities. For example, air pressure causes ear pain while flying, it allows skaters to skate faster on a highland track than on a lowland track and it is partly responsible for the changeable climate in any country. What is air pressure and how does it work?
Air Pressure In The Atmosphere
Air in the atmosphere is really nothing but a soup of constantly moving molecules. The molecules constantly collide with each other and with the environment. Due to gravity, most of the molecules are close to the Earth’s surface. The earth’s surface is constantly subject to collisions of molecules in the atmosphere.
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For example, there is an average constant number of collisions per unit of time with the earth’s surface. This causes a constant pressure of the atmosphere on the Earth’s surface. This is called air pressure. The pressure (p) is expressed in Pascal (Pa). The unit Pascal is again described as the force (Newton = N) per area (m²). This is exactly what pressure is. In formula form it looks like this:
- p = pressure = pressure (Pa)
- F = Force = force (N)
- A = Area = surface (m²
When a molecule collides, the molecule exerts a force that is provided by the kinetic energy (kinetic energy) contained in the molecule. The total force exerted by molecules per surface area determines the pressure. The number of molecules in the atmosphere, and thus the number of collisions, decreases with height. As a result, the air pressure in the atmosphere decreases with height.
Barometric pressure is a commonly used concept in meteorology. A well-known example is the weather map during the weather report on the television. Isobars make it clear where the high and low-pressure areas are located. An isobar is a line connecting locations on the Earth’s surface of equal air pressure. Here the pressure of air is still expressed in the unit bar or mbar (millibar). The unit bar is easy to convert to Pascal:
- 1 bar = 100,000 Pa
- 1 mbar = 100 Pa
On the weather map, these isobars are shown as lines in which the value of the pressure of air is shown in the bar. For example, low values for the pressure of air are found around a low-pressure area. The average pressure of air at the Earth’s surface worldwide is 1,013 bar.
Skating – Highland And Lowland Tracks
With the 2014 Winter Olympics in Sochi, barometric pressure has become a hot topic again. In skating, the air pressure is so important that a distinction is made between highland tracks and lowland tracks. A highland rink is an official skating rink located at a location far above sea level. The number of molecules in the atmosphere, and therefore the air pressure, decreases with altitude.
The pressure on a highland runway is therefore lower than on a lowland runway. As a result, skaters encounter less resistance during the race on a highland track. The number of molecules per surface is smaller so the skater needs to supply less energy to move air. At the high level of the Winter Olympics, this easily saves a few seconds.