1. The flow of water: Water is a fluid and has fluidity. When water is subjected to pressure, it flows from an area of high pressure to an area of low pressure. In a fire hose, a certain amount of pressure is usually applied at the water source to allow the water to flow to the fire scene.

2. Pressure transmission: The water pressure in the fire hose is provided through the water source. The water source can be a fire pump, fire hydrant or water tank, etc. The pressure provided by the water source pushes the water into the hose and maintains a certain flow rate and pressure.

3. Nozzle principle: The design of the nozzle at the end of the fire hose helps to spray water to the fire scene in the form of spray or atomization. Nozzles usually have specific shapes and hole sizes to control the direction and intensity of water flow. By adjusting the nozzle angle and water flow rate, it can be adapted to different types of fire situations.