The surface of Venus has been mapped with imaging radars aboard orbiting spacecraft. The radio signals used by these radar systems are able to penetrate the thick atmosphere, and the images produced by these instruments have given us spectacular views of the surface of Venus. The force of gravity tends to pull the molecules and particles toward the center of the body. The weight of the atmosphere pushing down on itself and on the surface of the planet creates atmospheric pressure. Balance inflated balloons on a dowel and observe what happens when the air is released from one of the balloons.
Pressure is equal to the force acting on an object divided by the area upon which it is acting.
The pressure exerted by an air mass therefore depends on the mass of the air and on the area below the mass. For a given air column, if the density of the air increases then the pressure exerted on the surface by the air column also increases. That is, of course, because the higher density means that the air column has greater mass and exerts a greater force on the area below it. Pressure is generally measured in units of Pascals . Atmospheric scientists, however, like to express pressure in units of bars .