Why does the flow increased when you open the valve and it will be reduced when you press on the end of the hose?

When you open the valve, you lower the resistance in the system, allowing more fluid to flow through the hose due to increased pressure and decreased friction. Conversely, pressing on the end of the hose creates a blockage, increasing resistance and reducing the flow rate as the fluid struggles to pass through the constricted area. This change in pressure dynamics illustrates the relationship between flow, resistance, and pressure in fluid systems.