Final answer:
Viscosity defines a fluid's internal resistance to flow, influencing the flow and pressure in systems like tubes or blood vessels. Poiseuille's law shows that very small changes in tube radius greatly affect flow, as radius has a fourth-power relationship. As viscosity increases, fluids flow slower, pressure drops occur, and viscous drag on moving objects increases.
Step-by-step explanation:
Viscosity is a measure of a fluid's resistance to flow. It describes the internal friction that occurs as different layers of a fluid move past one another. A fluid with high viscosity, like syrup, flows slowly, while a fluid with low viscosity, like water or juice, flows freely and quickly. Viscosity is expressed in units of poise (mPa.s), with higher values indicating a more viscous fluid. When contemplating fluid flow, Poiseuille's law is central in calculating flow and resistance in tubular systems like blood vessels. According to Poiseuille's law, flow is proportional to the pressure difference between two points and the fourth power of the radius of the tube, and inversely proportional to the fluid's viscosity and the length of the tube. This means that even a slight change in the radius can have a significant effect on flow due to its fourth-power relation. Pressure drops occur due to resistance, which increases as viscosity increases. Laminar flow is a flow regime characterized by smooth streaming fluid layers, which can be disrupted by high viscosity, leading to increased viscous drag on objects moving through the fluid. This relationship can be illustrated looking at the different flow profiles for viscous versus frictionless flow, where a viscous fluid will have the greatest speed at its center, declining towards the edges due to drag.