In streamline flow through a horizontal pipe of uniform cross section, Bernoulli's equation predicts that the pressure
- A. rises steadily along the pipe
- B. stays the same along the pipe for an ideal fluid
- C. falls to zero at the outlet
- D. depends on the colour of the pipe
Explanation
With constant area the speed is constant by continuity, and with no height change the potential term is constant too, so the pressure term must also be constant for an ideal fluid. Real fluids do lose pressure along such a pipe because viscosity dissipates energy, which is exactly the effect Bernoulli's equation leaves out. Comparing the ideal prediction with the real behaviour is how the role of viscosity is demonstrated.