What phenomenon occurs when the speed of water stream increases causing the entire stream to be agitated by resistance?

The phenomenon referred to in the question is critical velocity. This term describes the point at which the flow of a fluid, such as water, becomes turbulent due to increased speed. When the speed of the water stream reaches critical velocity, the flow can no longer remain smooth or laminar and begins to exhibit agitation. This agitation is caused by the turbulence, which arises from the fluid's resistance to flow changes in speed and direction.

In understanding fluid dynamics, critical velocity is crucial, as exceeding this limit means that the characteristics of flow will change significantly, potentially leading to challenges in systems designed to handle smooth, laminar flow.

Other terms mentioned, such as pressure resistance limit, water hammer, and cavitation, refer to different phenomena. Pressure resistance limit concerns the maximum pressure a system can tolerate before failure, water hammer describes a shock wave that occurs when fluid flowing in pipes is suddenly stopped, and cavitation refers to the formation of vapor bubbles in a liquid due to pressure reduction, not a change in speed itself. Each term represents distinct concepts within fluid mechanics.