Final answer:
In the context of firefighting, using lower nozzle pressures while increasing GPM allows firefighters to manage hand lines more easily, as it reduces the physical strain and aids in precision. The figures illustrate that nozzle pressure decreases due to gravitational effects and the conversion of potential to kinetic energy, yet the kinetic energy allows the water to exert a strong force on a fire.
Step-by-step explanation:
When managing large spray streams from fire hoses, hand lines can be more easily managed by adjusting the nozzle pressure. In firefighting, effective control of the hand lines is essential for directing the water stream towards the fire. To make this task more manageable, firefighters may use nozzles that operate at lower nozzle pressures while delivering a higher volume of water, measured in gallons per minute (GPM). Utilizing lower pressure allows for less strain on firefighters handling the hose and makes it easier to direct the stream, while increased GPM ensures that sufficient water is delivered to extinguish the fire.
In relation to the provided figures, one can understand that pressure in the nozzle of a fire hose is less than at ground level for two main reasons. Firstly, water has to travel uphill, which causes a pressure drop due to gravitational effects. Secondly, as the speed of water increases within the nozzle, there is a conversion of potential energy to kinetic energy, resulting in a pressure decrease. However, despite this reduced pressure at the nozzle, the flowing water can exert a significant force on a fire due to its kinetic energy. Once the water exits the nozzle and enters the air, its pressure equalizes with atmospheric pressure.