There are no minus numbers on the kelvin scale. The kelvin scale is a direct measure of the avg KE of the particles of a substance. 9.3 Gas pressure is a result of the collisions of gas particles on an object. Air exerts pressure because gravity holds air molecules in the earth's atmosphere. Atmospheric pressure results from the collisions of air molecules with objects.
Atmospheric pressure decreases as elevation increases.
Barometers measure atmospheric pressure. The particles of liquids are also in constant motion. They are free to slide past one another. Gases and liquids are both called fluids because they flow. The particles of a liquid are held together by weak attractive forces.