Field notebook

A dry fountain is not yet a diagnosis. Record a state, choose a boundary, measure a quantity that can discriminate between hypotheses, and calculate what the model predicts.

Observation becomes a control volume

Record basin level, visible water path, nozzle count and diameter, pipe access points, sound, vibration, and whether the pump is authorized to be observed operating. The control volume should say what crosses it: water mass, pressure work, and momentum. Do not open electrical enclosures or service submerged equipment; this page is for measurement and reasoning, not permission to work.

Three measurements buy three tests

Measure flow with a timed volume: Q = V/Δt. Measure jet height H_j and use the free-jet estimate v ≈ √(2gH_j) only after checking wind and nozzle angle. Measure pressure difference Δp across a component; its hydraulic power is ΔpQ. These measurements should agree within losses and uncertainty, not exactly.

Example: collecting 12 L in 6.0 s gives Q = 0.012/6 = 0.0020 m³/s. A 1.8 m jet implies v ≈ √(2·9.81·1.8) = 5.94 m/s. The corresponding nozzle area for that mean speed is A = Q/v = 3.37×10⁻⁴ m², equivalent to diameter 20.7 mm if the stream is one circular opening.

Rank hypotheses by prediction

• Water present but no motion: predict a pump, control, or intake problem, but distinguish them with an authorized observation of current, sound, or pressure.
• Pump running but weak jet: predict restriction or insufficient head; compare upstream pressure and flow with the pump curve.
• Flow present but poor display: predict nozzle geometry, wind, or level; compare individual jet heights and angles.

Each hypothesis must predict a measurement that could be wrong. A list of possible causes without such a measurement is not a physical model.

Report uncertainty, not theater

If a stopwatch measurement is 6.0 ± 0.2 s, then the fractional timing uncertainty is about 3.3%, and the same uncertainty enters Q if collected volume is exact. A jet-height estimate also inherits camera perspective and wind error. Report ranges, units, date, location, and who authorized the observation.

Work it out

Choose one visible fountain and write a one-page balance: measured inputs, unknowns, continuity equation, extended Bernoulli equation, Reynolds number, and one momentum reaction. State the assumption most likely to fail and the next safe measurement that would test it.