At observation stations around the world the air pressure reading, regardless of the observation station elevation, is converted to a value that would be observed if that instrument were located at sea level.

The common denominator we use is the sea-level elevation. Therefore, to give meaning to the pressure values observed at each station, we convert the station air pressures reading to a value with a common denominator. In fact, while the atmosphere extends more than 15 miles (24 km) up, one half of the air molecules in the atmosphere are contained within the first 18,000 feet (5.6 km).īecause of this decrease in pressure with height, it makes it very hard to compare the air pressure at ground level from one location to another, especially when the elevations of each site differ. Therefore, the air pressure is the same in the space station as the earth's surface (14.7 pounds per square inch).īack on Earth, as elevation increases, the number of molecules decreases and the density of air therefore is less, meaning a decrease in air pressure. In the International Space Station, the density of the air is maintained so that it is similar to the density at the earth's surface. In the atmosphere, air pressure can be exerted in all directions. Since molecules move in all directions, they can even exert air pressure upwards as they smash into object from underneath. The molecules therefore move with increased velocity striking the container's boundary with greater force and is observed as an increase in pressure. Adding heat to any particular container can transfer energy to air molecules. The second way of increasing (or decreasing) is by the addition (or subtraction) of heat. The increased number of collisions forces the tire's pressure increase to expand in size. By adding air, the number of molecules increase as well the total number of the collisions with the tire's inner boundary.

A larger number of molecules in any particular container will increase the number of collisions with the container's boundary which is observed as an increase in pressure.Ī good example of this is adding (or subtracting) air in an automobile tire. First, simply adding molecules to any particular container will increase the pressure. However, when we sum the total forces from the large number of molecules that strike a surface each moment, then the total observed pressure can be considerable.Īir pressure can be increased (or decreased) one of two ways. Despite their tiny size, when they strike a surface they exert a force on that surface in what we observe as pressure.Įach molecule is too small to feel and only exerts a tiny bit of force. The atoms and molecules that make up the various layers in the atmosphere are constantly moving in random directions. Air Pressure The number of molecules in the

Put something in the air