Answer: decreases.
- A increases
- B decreases
- C remains unchanged
- D first rises then falls
Correct answer: B. decreases
Explanation: Increased molecular motion weakens cohesive forces, so surface tension falls with rising temperature.
Since the same volume of fluid must pass every cross-section per second (continuity), the fluid speeds up where the pipe narrows; Bernoulli's equation then says this faster-moving fluid has lower pressure - the principle behind a venturi meter and an aircraft wing's lift.
Concept context
Pressure, buoyancy, Bernoulli equation, viscosity, and surface tension.