Viscosity, Poiseuille Flow and the Reynolds Number · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Sticky flow, narrow pipes, rough flow

Science · Forces & Motion · ages 20-21
Name ______________________   Date ____________

  1. Which quantities combine into the Reynolds number?

    • Density, speed, length, and viscosity
    • Pressure, volume, and temperature
    • Mass, charge, and spring constant

  2. At fixed pressure difference, halving a pipe radius cuts the flow rate by what factor?

    • 2
    • 4
    • 16

  3. In steady pipe flow the fluid moves fastest right at the walls.

    Circle one:   True   False

  4. The Reynolds number in a pipe sits far above the threshold. What should you expect?

    • Smooth laminar flow with low loss
    • Eddies, mixing, extra loss, and noise
    • The flow to stop entirely

  5. A pipe carries 3 units of flow. Its radius is doubled at the same pressure difference. What is the new flow rate?

    Answer: ______________

  6. In which situation may the Bernoulli equation be applied?

    • Steady laminar flow with negligible viscosity
    • Flow through a thin long sticky pipe
    • Fully turbulent flow with large losses

  7. Density 1000, speed 1, length 0.01, viscosity 0.01. Multiply the first three and divide by the last. What is the Reynolds number?

    Answer: ______________

  8. A student applies Bernoulli to honey creeping through a thin long tube. Why is that wrong?

    • Honey is too dense to have pressure
    • Viscous shear losses dominate, so energy is not conserved
    • Bernoulli only works for gases
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Answer key

For grown-ups. Fold this page away before handing over the rest.

Sticky flow, narrow pipes, rough flow W1-mt_-1sWgkRtMs-s1

  1. Density, speed, length, and viscosity · Those four combine into one unit free number.
  2. 16 · One half to the fourth power is one sixteenth.
  3. False · The profile is parabolic: fastest in the middle, still at the walls.
  4. Eddies, mixing, extra loss, and noise · Past the threshold, disturbances grow faster than they damp.
  5. 48 · Two to the fourth is 16, and 3 times 16 is 48.
  6. Steady laminar flow with negligible viscosity · Bernoulli needs the energy budget conserved along a streamline.
  7. 1000 · 1000 times 1 times 0.01 is 10, over 0.01 is 1000.
  8. Viscous shear losses dominate, so energy is not conserved · Sticky losses eat the budget Bernoulli assumes stays intact.
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