SESKStuff Everyone Should Know
SESK: Stuff Everyone Should Know · sesk.info/eng-continuity-narrow-pipe

In steady incompressible flow, what happens to speed where a pipe narrows?

The fluid speeds up.

Start playing free

  1. It speeds up ✔
  2. It slows down
  3. It must stop

Why: The same volume must pass each cross-section per second. Since A1v1 = A2v2, a smaller area requires a larger average speed.

Huh, didn't know that: For compressible gas flow, density changes must be included in mass continuity.

The dad joke
The pipe went on a diet and the fluid picked up the pace.
Like this card?
Play the game

References

Answer: It speeds up. The same volume must pass each cross-section per second. Since A1v1 = A2v2, a smaller area requires a larger average speed.

  1. OpenStax University Physics Volume 1, Fluid Dynamics openstax.org/books/university-physics-volume-1/pages/14-5-fluid-dynamics
    because the cross-sectional area of the pipe decreases, the velocity must necessarily increase
    Checked 2026-10-10.

Think this answer is wrong? Tap "Challenge this answer" on the card in the game and tell us why.

Test yourself in the game

EngineeringA 12-tooth motor gear drives a 36-tooth wheel gear. Ideally, what happens to the output torque?EngineeringFor flow in a smooth tube, which Reynolds number is clearly in the turbulent range?EngineeringHow many base units does the International System of Units (SI) have?

That's stuff everyone should know.