According to the time-averaged expression for an alternating electric field, the normalized electromagnetic pressure is proportional to the square of the voltage intensity and inversely proportional to the square of the voltage repetition frequency. Moreover, the plasma propagation velocity is either directly proportional, inversely proportional, or nonproportional to the normalized electromagnetic pressure at all neutral gas flow rates. Because the plasma current is only directly proportional to the normalized electromagnetic pressure at all neutral gas flow rates, the dependence of the plasma density on the electromagnetic pressure changes to obtain a balance of dependence. In the momentum transfer equation, plasma density does not originally depend on electromagnetic pressure, but the dynamic pressure associated with the neutral gas flow also exerts a force on the plasma through collisions. Therefore, when the ionization generation of plasma by collisions between the plasma and neutral particles is dominant over recombination by collisions, the plasma density is square proportional or directly proportional to the electromagnetic pressure.