Atkinson friction factor is a measure of the resistance to airflow of a duct.
It is widely used in the mine ventilation industry but is rarely referred to outside of it.
Atkinson friction factor is represented by the symbol
It is related to the more widespread Fanning friction factor by
is the density of air in the shaft or roadway under consideration and
It was introduced by John J Atkinson in an early mathematical treatment of mine ventilation (1862) and has been known under his name ever since.