Drag equation by experiment. Of particular importance is the formula_8 dependence on flow velocity, meaning that fluid drag increases with the square of flow velocity. When flow velocity is doubled, for example, not only does the fluid strike with twice the flow velocity, but twice the mass of fluid strikes per second. Therefore, the change of momentum per second is multiplied by four. Force is equivalent to the change of momentum divided by time. This is in contrast with solid-on-solid friction, which generally has very little flow velocity dependence. The drag force can also be specified as, formula_9 where, "P" is pressure
Thermal velocity Boltzmann constant, formula_2 is the temperature, and formula_3 is the mass of a particle, then we can write the different thermal velocities: If formula_4 is defined as the root mean square of the velocity in any one dimension (i.e. any single direction), then If formula_4 is defined as the mean of the magnitude of the velocity in any one dimension (i.e. any single direction), then If formula_4 is defined as the most probable speed, then If formula_4 is defined as the root mean square of the total velocity (in three dimensions), then If formula_4 is defined as the mean of