Hoses and nozzles come in different sizes. In order for them to be effective, nozzle pressure must be carefully determined. If the water has to travel up an incline, this will increase the amount of pressure required to deliver it to the fire. Finally, as the water travels through the hose, it will lose some of its energy to friction. Depending on the hose and nozzle size, the firefighter must further calculate how much energy will be sacrificed due to friction.
Firefighters use friction loss charts in their calculations.
Make a wrong calculation, and you risk letting the fire get out of control. In groups of four or five, demonstrate the concepts of pressure and friction by completing the following activities. Three of the group members should each place a thumb over each of the three holes, while a fourth fills the bottle with water. Ensure that the three people who are blocking the holes have graduated cylinders. At the given signal, the three will simultaneously take their thumbs away from the holes and catch the draining water with their graduated cylinder.