There are two types of resistance in one system: linear and local.

Linear resistances appear when there is internal friction between particles or friction of the fluid against the surface of the pipe or channel. They are called frictional resistances or linear resistances. When the motion of fluids deforms or changes its direction or velocity then some loss of energy that is called local, occurs. This local loss appears most often when the fluid is conveyed by means of air pipelines. Forced air heating.

Linear resistances can be found where there is a straight section in the distributing system. When the size of the pipe increases, the relative surface of friction against the pipe walls becomes smaller. When length increases, losses grow linearly.

It was also proved that reserving the fluid density depends on the wall roughness of the pipes, in which the fluid flows.