Domain: Engineering — Hydraulic Engineering
Target concept: Atmospheric pressure

Video generation prompt: A U-tube manometer is connected to a horizontal pipe with a diameter of 2 cm on the left side, and the right side is open to the atmosphere. The pipe is filled with water at normal temperature. Operation: gradually increase the flow velocity within the pipe and observe the change process of the liquid level height difference in the U-tube.

Evaluation guide:
(i) Target concept: Pressure differential induced by dynamic flow in an incompressible fluid, measured via hydrostatic column imbalance in a U-tube manometer.
Minimum mechanism: Water must be incompressible and Newtonian; pipe flow must be steady, fully developed, and subsonic; U-tube fluid must be the same water (no density mismatch); gravitational field must be uniform and vertical; open limb must experience ambient atmospheric pressure without obstruction.
(ii)Storyline: Frame 0–2s: Static baseline: U-tube limbs show equal water levels; pipe is full and still; flow-control element is in initial position. Frame 2–4s: Flow initiation: control element moves (e.g., valve rotates), coinciding with first detectable divergence of water levels. Frame 4–8s: Progressive response: left limb level ascends steadily while right limb descends, maintaining constant total column length; no overshoot or oscillation. Frame 8–10s: Stabilized differential: height difference persists at maximum value; water surfaces remain quiescent and horizontally aligned; all objects retain fixed spatial relationships under consistent lighting. Perspective: Fixed frontal, eye-level view capturing entire U-tube, pipe junction, and flow-control element in single unoccluded shot; no camera motion, zoom, or cut.

Manual:
Experimental Procedure
1. Show fixed side-by-side view: left — horizontal water-filled pipe (2 cm diameter) connected to U-tube manometer; right — open end of U-tube exposed to air.
2. Activate flow-control cue (e.g., rotate valve handle or press button icon) to increase flow velocity in pipe.
3. Observe liquid level difference developing between left (pipe-connected) and right (open) limbs of U-tube.
Observation of Experimental Phenomena
- Left limb level increases; right limb level decreases.
- Height difference widens progressively as flow velocity increases.
- Water remains continuous, transparent, and fully fills both limbs and pipe.
Summary of Experimental Principles
- Based on Bernoulli’s equation: increased flow velocity in the pipe lowers the static pressure at the connection point below atmospheric pressure; atmospheric pressure acting on the open (right) limb then pushes water toward the lower-pressure left limb, raising the left level and lowering the right — manifesting as measurable height difference Δh ∝ v².

Prompt Grounding rubric:
level_1: No U-tube manometer appears, or no horizontal pipe is shown, or neither limb of the U-tube contains visible water, or there's no way to tell the pipe-connected limb apart from the open limb, or nothing on screen suggests the flow is being increased (no valve, no dial, no motion cue in the pipe).
level_2: A U-tube is shown but not actually joined to the pipe, or the pipe is shown but not joined to the U-tube; water shows up in the pipe or in only one U-tube limb instead of filling both; it isn't clear which limb is connected to the pipe and which is open (no consistent left/right layout); nothing on screen hints that the flow velocity is changing.
level_3: The U-tube's left limb is visibly joined to the horizontal pipe, and its right limb is open to the room air with nothing capping it; the pipe is clearly horizontal and full of water; the pipe and the open limb sit side by side in the same shot; something on screen signals the flow is being increased, such as a valve handle turning, but the water levels in the two limbs haven't visibly changed yet.
level_4: Everything in score 3 holds true, and in addition: the two limbs of the U-tube visibly settle at different heights at some point in the clip, with the height difference appearing only between the left (pipe-connected) and right (open) limb; no other tubes or liquids are added; the pipe stays on the left and the open limb on the right throughout; the level change only begins after the flow-increase cue happens.
level_5: Everything in score 4 holds true, and in addition: the causal order is visible on screen: the flow-increase cue happens first, then the level gap opens; the left (pipe-connected) limb's water level rises while the right (open) limb's level falls, with the total water in the U-tube visibly conserved; both limbs hold plain water with no bubbles, dye, or added layers; the pipe's width looks the same along its length with no narrowing, flaring, or blockage; the camera angle never makes the two limbs' heights hard to compare.

Scientific and Causal Correctness rubric:
level_1: Both U-tube limbs stay at the same height the whole time; or both levels rise or fall together instead of one going up while the other goes down; or the open (right) limb is shown capped or sealed; or the pipe carries something other than water; or the water changes color or turns cloudy as the flow increases; or a height difference is already present before the flow-increase cue happens.
level_2: The two limbs settle at different heights, but in the wrong direction for Bernoulli's principle: the left (pipe-connected) limb falls while the right (open) limb rises; or the height gap keeps growing even while the flow-increase cue is inactive; or one limb empties out completely; or air pockets appear and grow or shrink in the pipe as the flow changes; or the U-tube fluid is visibly not water, with nothing indicating it should behave like water.
level_3: The left (pipe-connected) limb's level rises and the right (open) limb's level falls, settling into a stable height difference; the water in both limbs and the pipe stays clear and uniform with no boiling or phase change; the flow-increase cue clearly happens before the levels start to shift; however, the height difference appears suddenly at its final size, or wavers back and forth, instead of growing steadily.
level_4: Everything in score 3 holds true, and in addition: the height difference grows steadily, whether in visible steps or smoothly, over the course of the clip, with no reversal and no leveling-off before the video ends; both water surfaces stay flat and calm, with no splashing or upside-down meniscus; the pipe stays completely full of water with no gaps or intermittent flow; nothing like fogging, condensation, or evaporation gets in the way of seeing the levels clearly.
level_5: Everything in score 4 holds true, and in addition: the pace of the level change visibly tracks the flow-increase cue: as the valve handle turns further, the height gap widens to match, rather than jumping ahead of or lagging far behind it; both water surfaces stay level with the horizon in every frame; the two limbs' surfaces can be compared directly with no camera-angle misalignment; no glare, reflection, or distortion hides the true water heights; the curve of the meniscus looks the same shape in both limbs.

Spatiotemporal Consistency rubric:
level_1: The U-tube or pipe suddenly jumps to a new spot between shots; the two limbs disconnect and reconnect mid-video; the water surface vanishes for a stretch of frames instead of moving continuously; the lighting suddenly flashes, strobes, or drops into full shadow; the U-tube or pipe stretches or skews in a way no rigid object would; the background shifts independently of the U-tube and pipe.
level_2: The U-tube stays roughly in place but visibly trembles more than ordinary handheld camera motion would explain; the curved meniscus looks a different shape in the two limbs, or changes shape oddly over time; the spot where the pipe meets the U-tube visibly widens and narrows with no physical cause; the lighting brightens and dims unevenly instead of staying steady; shadows separate from the objects casting them or fall in a direction that doesn't match the light.
level_3: The U-tube, its connecting pipe, and the valve handle hold fixed, unchanging positions through the whole clip: nothing jumps, resizes, or spins; the color and direction of the lighting stay constant; every shadow stays attached to its object and points the same way in each frame; the water in each limb rises or falls smoothly with no skipping or freezing; the outlines of the tube and pipe stay crisp, without drifting in and out of focus.
level_4: Everything in score 3 holds true, and in addition: there's no drifting, blurring, or refocusing anywhere in the clip; the water surfaces move fluidly with no stuttering, freezing, or repeated frames; the joint between the pipe and the U-tube shows no gap or separation at any point; the lighting stays even across both limbs and the pipe; there's no lens flare, color fringing, or vignetting that makes it hard to compare the two water levels.
level_5: Everything in score 4 holds true, and in addition: the water surfaces and their curved menisci show no motion blur even as the levels change; the U-tube and pipe's outlines stay crisp and steady with no shimmering or flickering edges; landmarks like the U-tube's rim or the valve handle stay at a constant, fixed spot on screen throughout; the highlight pattern on the two water surfaces looks the same in both limbs at any given moment; no smudging, blockiness, or noise appears over the menisci, the inside of the pipe, or the pipe-to-U-tube joint that would make the two levels hard to read.