The most basic atmospheric element is air pressure. Pressure itself is a measure of the force per unit area. The concept of force is usually best understood by considering Newton's second law, which states that the acceleration of a body is directly proportional to the force exerted on that body and inversely proportional to its mass. In other words, force (F) is equal to the product of mass (M) and acceleration (a).

Using International System (SI) units of measure, M is given in kilograms (kg) and acceleration in units of meters per second per second (m/s2, also expressed as m s-2). Given F = Ma, then force is described in units of kg m s-2, which is a newton. A newton (N) is equal to the ...