In fluid mechanics, which property best describes a fluid's resistance to flow (internal friction) and distinguishes real fluids from ideal (inviscid) fluids?

• A. Pressure
• B. Density
• C. Viscosity
• D. Surface tension

Answer: (C)

Verified step by step guidance

1. Understand that the problem is asking for the property of a fluid that quantifies its resistance to flow or internal friction.
2. Recall that ideal fluids are considered inviscid, meaning they have no viscosity and thus no internal resistance to flow.
3. Identify that viscosity is the physical property that measures a fluid's internal friction, which causes resistance when layers of fluid move relative to each other.
4. Recognize that pressure and density are important fluid properties but do not describe internal friction or resistance to flow.
5. Conclude that viscosity is the key property that distinguishes real fluids (which have viscosity) from ideal fluids (which do not).