Domain: Healthcare — Digestive Physiology
Target concept: Gastric pH Measurement (Simulated Paper Test)

Video generation prompt: Place a pH strip on a clean surface. Use a pipette to apply simulated gastric fluid onto the pH strip. Wait for a moment, then compare the pH strip with a standard pH color chart to determine the acidity. Demonstrate clear hand movements, the pH strip, the pipette, and the reference color chart.

Evaluation guide:
(i) Target concept: Visual verification of gastric acidity via pH indicator chemistry.
Minimum mechanism: pH-sensitive dye in strip pad must undergo reversible protonation in response to H+ ions in simulated gastric fluid, producing a chromophore with absorption peak in orange-red spectrum; color chart must encode this spectral correspondence as discrete labeled bands.
(ii)Storyline: Frame 1–2: Clean surface visible, pH strip placed centered and flat. Frame 3–4: Pipette enters frame from upper right, tip descending toward strip pad. Frame 5: Pipette tip contacts pad; fluid appears as cohesive amber droplet. Frame 6–7: Pad uniformly wets and transitions from pale yellow to orange-red. Frame 8–10: Strip lifted slightly and positioned adjacent to color chart; final hue aligns precisely with pH 2 band under consistent lighting; viewpoint remains fixed frontal close-up, hands fully visible, no background distraction.

Manual:
Experimental Procedure
1. Place pH strip flat on clean, dry surface.
2. Use pipette to dispense simulated gastric fluid onto strip"s reactive pad.
3. Wait 1–2 seconds, then hold strip adjacent to standard pH color chart for visual comparison.
Observation of Experimental Phenomena
The pH strip"s reactive pad changes from pale yellow to vivid orange-red within 2 seconds of fluid application; this final color matches the pH 2 band on the chart.
Summary of Experimental Principles
Gastric fluid is highly acidic (pH ≈ 1.5–3.5); pH indicator strips contain dyes that undergo protonation-dependent color shifts; the observed orange-red color corresponds to pH ~2, confirming normal gastric acidity.

Prompt Grounding rubric:
level_1: None of the four required items (pH strip, pipette, simulated gastric fluid, color chart) appear together in a gastric-pH testing scene; the clip shows something unrelated to a pH strip test, or shows only isolated objects with none of the placement/application/comparison actions happening.
level_2: At least one of the four items appears, but the video shows fewer than two of the three actions (placing the strip, applying fluid with the pipette, comparing strip to chart); or two items appear yet none of the three actions is actually carried out, or the chart is shown before the strip has been treated with fluid.
level_3: The pH strip, pipette, simulated gastric fluid, and color chart all appear; the strip is placed on a surface, fluid is applied to it with the pipette, and the strip is then held up next to the color chart, in that order, but at some point one item is hard to see (e.g., blocked by a hand) or the chart is not actually next to the strip when the comparison happens.
level_4: All four items are clearly shown and used correctly: the strip is placed flat first, the pipette tip touches the strip to deliver fluid, the fluid visibly wets the strip, and the strip and color chart are held side by side for the comparison; only minor incidental issues remain, such as a brief hand tremor or a moment of soft focus that does not hide any of the four items or actions.
level_5: The pH strip (with its colored reactive pad), pipette (bulb and tapered tip), simulated gastric fluid, and labeled color chart are all unmistakable throughout; the strip is set down first, the pipette delivers fluid onto the strip pad only (no fluid missing the pad or dripping elsewhere), the fluid visibly soaks the pad, and the strip and chart are then shown adjacent to each other with both fully unobstructed during the comparison; the order of these steps is never reversed or skipped.

Scientific and Causal Correctness rubric:
level_1: The strip's pad never visibly changes color after fluid is applied, or it changes to a color outside the red/orange/yellow acidic range (e.g., turns blue, green, or purple), which would be inconsistent with a strongly acidic gastric fluid simulant.
level_2: The strip's pad changes color, but the resulting hue does not resemble any band shown on the color chart, or the chart itself is missing its pH number labels, or the fluid used looks like plain water and the strip shows a neutral color (e.g., green) rather than an acidic one, none of which fits gastric fluid's expected strong acidity.
level_3: The strip's pad shifts from its pale baseline color to a yellow-orange-to-red acidic hue soon after the fluid is applied; the color chart shows bands labeled for low pH (roughly 1-3) that are each a visibly different hue; the strip's final color falls somewhere in that acidic part of the chart, but it's hard to tell which single band it matches most closely, or the color still looks like it's fading in or only partly developed when compared.
level_4: The strip's pad shows an unambiguous shift from pale yellow to a vivid red-orange after the fluid is applied; the chart's pH 1, 2, and 3 bands are each a visibly distinct hue; the strip's developed color clearly resembles one specific band (around pH 2) rather than sitting between two bands; the color looks fully and evenly developed across the pad, not patchy, when the comparison happens.
level_5: The strip's pad starts pale yellow and dry, then becomes fully and evenly soaked and colored (no dry patches, no uneven blotching) within a couple of seconds of the fluid touching it; the resulting red-orange hue is visually indistinguishable from the chart's pH 2 band when viewed under matching lighting; the chart shows pH 1 (deepest red), pH 2 (orange-red), and pH 3 (orange) as clearly graded, distinguishable colors; during the comparison the strip and its matching band sit close together under similar lighting, making the match obvious to the eye.

Spatiotemporal Consistency rubric:
level_1: The pipette or strip appears or disappears abruptly between moments; the strip looks fully wet and colored before the pipette ever gets near it; the color chart pops into frame only after the strip's color has already settled, then disappears again; the room lighting suddenly changes partway through (e.g., an overhead light going out); the pipette visibly bends or the strip visibly folds in a way real objects wouldn't.
level_2: The pipette approaches the strip but its tip never appears to actually reach the pad; fluid shows up on the strip even though the pipette is not close enough to have delivered it; the strip's color starts changing before the fluid has finished landing on it; the color chart enters the frame only after the strip is already colored, then stays still while the strip keeps moving; the lighting flickers or casts inconsistent shadows across the placement, application, and comparison steps.
level_3: The strip, pipette, and chart stay reasonably consistent in size, position, and orientation relative to one another throughout; the pipette tip stays visibly close to the strip while approaching and touching it; the fluid transfer looks like one continuous motion rather than a jump-cut to an already-wet strip; the strip stays put on the surface the whole time; the chart stays in the same spot during the comparison; nothing about the strip, pipette, or chart appears to stretch, warp, or morph; a brief, barely noticeable hand occlusion of the pipette base is acceptable.
level_4: The pipette tip moves smoothly and continuously from the air down to contact with the strip pad, with no jump in its path; the fluid spreads outward from the contact point without skipping ahead; the strip does not shift, rotate, or lift up during or right after the fluid is applied; the chart stays rigidly in the same relative position and angle once it enters the comparison shot; the lighting looks consistent across the whole sequence, with no highlight or shadow suddenly relocating; every motion (pipette lowering, fluid spreading, strip being lifted) looks physically natural, with nothing floating or defying gravity.
level_5: The pipette's path toward the strip is smooth and steady from start to finish, ending right at the center of the pad; the fluid only starts appearing at the moment of first contact and spreads outward with a clean, consistent edge; the strip stays completely flat and still, with no visible shift or drift in its position at any point; the chart stays in the same screen position and orientation throughout the comparison; the lighting's brightness and direction look identical from the first frame to the last, with no sudden glare or dimming; the pipette's and strip's movements look smooth and natural throughout, without any visible stutter, freeze, or jump.