Water flow, pressure, distance, angle, surface, and contaminant all conspire to make each new job a unique challenge, one that doesn't answer to a single equation, benchmark, or rule of thumb. So it can only help to have a little more knowledge about the physics of pressure washing, especially as the business gets more competitive. Force a volume of water through a confined space under high pressure, and a stream of water will emerge to strike whatever surface lies in front of it. Crank up the pressure a bit, and it'll strip the grime stuck to a brick wall. If, that is, the operator doesn't know what's going on.
Pressure washing uses just a few physics concepts.
The machine is only a glorified garden hose, and the same rules apply to both devices. Impact force is the figure obtained by calculating the amount of water being thrown at a surface with regard to the pressure at which it is being moved. This figure enables you to compare the power of machines with different pressure and flow rates. Therefore, unless you know what you want to accomplish with your pressure washer, and how those variables interact, numbers like impact force, gpm, psi, etc., will be useless. But move off to a nice angle, and that paint begins to peel right off, even though the theoretical cleaning energy striking the surface is greatly reduced.