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
Komar mass knowledge of the components of formula_37, we can see that K = formula_3. If we chose our spatial coordinates so that we have a locally Minkowskian metric formula_39 we know that With these coordinate choices, we can write our Komar integral as While we can't choose a coordinate system to make a curved space-time globally Minkowskian, the above formula provides some insight into the meaning of the Komar mass formula. Essentially, both energy and pressure contribute to the Komar mass. Furthermore, the contribution of local energy and mass to the system mass is multiplied by the local "red shift" factor