Backward Reaction Force in a Firehose

Excerpt

Because the ejected water jet in a firehose resembles the ejected gases that propel rockets, many people believe that the ejected water jet produces a backward reaction force on the firehose, a force that must be counteracted by firefighters. In a previous experimental work published in this journal [1] we showed that the reaction force produced at the nozzle does not exist and that the force counteracted by firefighters exists but is a consequence of the interaction of water with the inner walls of a bent hose. In a recent paper in this journal entitled Firefighter Nozzle Reaction, Selena K. Chin, Peter B. Sunderland, and Grunde Jomaas [2], concluded that the water jet momentum ejected from a firehose is produced at the nozzle and that the backward nozzle reaction in a firehose is always equal to the jet momentum flow rate. Although this backward force on the firefighters apparently agrees in magnitude and direction with firefighting experience, it contradicts the experiment reported in our previous work [1]. Here, we argue that Chin et al. results are the consequence of using an equation for the tension of the hose that is difficult to reconcile with a conceptual understanding of the force on the nozzle and with calculations found in two Fluid Mechanics textbooks cited in their paper [3, 4]. …