Physics Kinetic Theory

Through isotropy, we can say it enables equal distribution of velocity components in all directions. This allows us to replace directional velocity terms with a fraction of the total velocity squared. That basically simplifies the pressure formula to involve only rms speed.

This is because pressure is a result of how momentum transfers during collisions. We also know that momentum depends on velocity. The derivation shows that pressure is proportional to the average of squared velocities. That we know from the root-mean-square (rms) speed.

Surprisingly, the viscosity of a dilute gas behaves exactly opposite to what you might expect for liquids. Liquid viscosity generally decreases as temperature is lowered. The viscosity of a dilute gas increases as and when you raise its temperature. This counter-intuitive behaviour was clearly established experimentally and is explained by the kinetic theory.

It's because gas molecules constantly move around at super high speeds. They randomly bump into each other constantly. Gravity does pull on them. The pulling effect is not much, however. When we consider the distance from the floor to the ceiling, gravity's pull is overcome by the molecular kinetic energy. So they just spread out and move from one place to another. They can't settle down.