Domain: Healthcare — Clinical Laboratory Science
Target concept: Urinalysis pH Determination

Video generation prompt: A 1 mL sample of fresh urine from a healthy adult was placed in a test tube. Two drops of methyl red indicator were added, the solution was mixed thoroughly, and the change in solution color was observed.

Evaluation guide:
(i) Target concept: Visual verification of acid-base indicator response in clinical urinalysis.
Minimum mechanism: Methyl red must be chemically present and react stoichiometrically with H⁺ ions in urine; the resulting chromophore must absorb/reflect light to produce orange-red hue; human vision must resolve this hue unambiguously under standard illumination.
(ii)Storyline: [Frame 0–2] Static shot: upright test tube with 1 mL pale yellow urine. [Frame 3–4] Dropper enters frame from top; two discrete droplets detach and fall vertically into tube. [Frame 5–7] Tube begins smooth, continuous swirling motion; liquid rotates cohesively without splashing. [Frame 8–10] Motion stops; final orange-red solution fills tube uniformly, held steadily in focus with full visibility of color and clarity.

Manual:
Experimental Procedure
1. Place 1 mL fresh urine (pale yellow, translucent) in a clear test tube.
2. Add exactly two drops of methyl red indicator using a calibrated dropper.
3. Mix thoroughly by gentle swirling or inversion.
Observation of Experimental Phenomena
Urine solution changes from pale yellow to uniform orange-red after mixing.
Summary of Experimental Principles
Methyl red is a pH indicator that turns red below pH 4.4, orange-red at pH ~5–6, and yellow above pH 6.2. Healthy adult urine typically has pH ~6.0, yielding an orange-red endpoint.

Prompt Grounding rubric:
level_1: No test tube appears; no urine sample is visible; there's no methyl red bottle or dropper; no mixing action occurs; there's no moment where a resulting color could be observed.
level_2: A test tube holding some liquid appears, but the liquid is never identifiable as urine; a dropper or indicator bottle appears but no droplet is shown entering the tube; there is no mixing motion and no resulting color is ever shown.
level_3: A clear test tube holds a pale yellow liquid (urine); two drops from a dropper are shown entering the liquid; the tube is swirled or inverted to mix; a final liquid color is shown, but only briefly, partly out of frame, or too blurred to read clearly.
level_4: The test tube, the pale yellow urine, the indicator bottle and dropper, and two visible droplets entering the tube are all shown; the tube is swirled or inverted for at least a second; the resulting liquid color is shown clearly and in full view once mixing stops.
level_5: In addition to the above, exactly two droplets enter the tube one after the other and visibly merge into the liquid, the swirling motion is smooth, continuous, and covers the whole liquid volume, and the final color is held steadily on screen for at least half a second with no occlusion, blur, or cut interrupting the view of it.

Scientific and Causal Correctness rubric:
level_1: There's no visible link between adding the indicator and any color change; the final color is blue or purple (which would indicate an alkaline sample, not typical urine) or stays pale yellow throughout; overall, nothing in the liquid's appearance changes across the whole clip.
level_2: The indicator is added, but the final color is green (a muddy in-between shade) or violet, neither of which matches typical urine's mildly acidic pH range; or a color change happens before the drops are added, or without any mixing shown.
level_3: The two drops are added and mixed in, and the liquid shifts from pale yellow toward an orange-red shade, but the shade is ambiguous, more brownish or washed-out than a clear red-orange, making it hard to read as a confident acidic result.
level_4: The final liquid is an unambiguous, saturated orange-red with no leftover yellow patches or purple tinge, and the color looks even throughout the liquid column.
level_5: The final orange-red color is vivid and fully saturated with no trace of yellow or purple anywhere in the tube, matches what a genuinely acidic urine sample would look like with methyl red, and holds steady without fading or streaking once mixing has finished.

Spatiotemporal Consistency rubric:
level_1: The test tube seems to vanish and reappear between shots; the liquid level changes with no visible cause; the dropper appears already inside the tube with no approach shown; the swirling motion starts or stops abruptly with a visible skip or warp in the footage.
level_2: The tube stays on screen but shifts position or rotates unnaturally between the dropping and mixing steps; the two droplets appear already formed in mid-air with no visible fall; the swirling motion pauses oddly partway through; the lighting changes noticeably between one step and the next for no clear reason.
level_3: The tube stays in one place throughout; the droplets fall and land in the liquid smoothly; the swirling is one continuous, plausible motion; nothing about the tube's shape or position breaks between steps; but the lighting on the tube shifts slightly, or a shadow beneath it changes, between the dropping and mixing shots.
level_4: The dropper tip stays aligned right above the tube's opening while dispensing; the tube's base stays put on the surface; the liquid stays still until the swirling begins; there's no flicker, warping, or sudden shift in viewing angle; the motion throughout keeps a steady, natural pace.
level_5: The whole sequence (the drop falling, landing, merging, and swirling) flows as one unbroken chain of motion; the tube does not visibly move, tilt, or change size across the clip; the liquid's surface dips and settles in a way that looks physically plausible during mixing; and the light falling on the tube and the shadow it casts on the bench stay just as bright and point the same way from the first frame to the last.