Domain: Natural Science — Environmental Science
Target concept: Hardness Test of Water (Soap Bubble Method)

Video generation prompt: Take two test tubes, add hard water to tube A and soft water to tube B, respectively. Add two drops of soap solution to each, then shake.

Evaluation guide:
(i) Target concept: Differential foam stability as a visual proxy for water hardness via ion-mediated soap precipitation.
Minimum mechanism: Soap anions must encounter divalent cations (Ca²⁺/Mg²⁺) in tube A to form insoluble calcium stearate/magnesium stearate scum, suppressing foam nucleation and destabilizing existing foam; tube B lacks these ions, enabling micelle formation and stable foam lamellae.
(ii)Storyline: Frame 1–2: Static side-by-side view of unlabeled/unfilled tubes → Frame 3–4: Tubes filled (A with hard water, B with soft water) → Frame 5: Two drops added to each tube (visibly distinct impact) → Frame 6–7: Simultaneous shaking of both tubes (identical motion onset/duration) → Frame 8–10: Foam emerges and evolves differentially: tube A shows transient or absent foam; tube B shows continuous, voluminous foam. All events occur from fixed frontal viewpoint with no camera movement; tubes remain fully in frame and in focus throughout; foam state must be legible without zoom or annotation.

Manual:
Experimental Procedure
1. Place two identical test tubes side-by-side: label left tube A, right tube B.
2. Fill tube A with hard water, tube B with soft water.
3. Add exactly two drops of soap solution to each tube.
4. Shake both tubes vigorously and simultaneously for ~2 seconds.
Observation of Experimental Phenomena
Tube A (hard water): little or no stable foam forms; any foam collapses rapidly.
Tube B (soft water): abundant, persistent foam forms and remains stable.
Summary of Experimental Principles
Hard water contains Ca²⁺/Mg²⁺ ions that react with soap anions to form insoluble scum, preventing lather. Soft water lacks these ions, allowing soap to form stable foam.

Prompt Grounding rubric:
level_1: No test tubes are visible; or soap solution is never added; or only one tube appears in the shot; or there is no way to tell which tube holds hard water and which holds soft water; or neither tube is ever shaken; or the two tubes are never shown together in the same frame.
level_2: Two test tubes appear, positioned or labeled as A and B, but the labels are illegible or don't match the hard/soft assignment; soap solution is added to only one of the two tubes; shaking happens for only one tube; or the two tubes are never both in frame at the same time.
level_3: Two test tubes labeled A and B (or unambiguously distinguishable as left/right) appear together in the same frame; soap solution is visibly added to both tubes (two drops per tube, or two clearly separate addition events); both tubes are shaken; tube A holds hard water and tube B holds soft water, matching the prompt.
level_4: All conditions for the 3-score level are met, and in addition: tube A and tube B keep the same left/right positions for the entire video; any labels stay legible and consistent whenever the tubes are visible; soap solution is added to both tubes before either is shaken; neither tube is removed, replaced, or re-labeled partway through.
level_5: All conditions for the 4-score level are met, and in addition: both tubes are held at the same tilt and height, are the same type and size of transparent glass tube, hold the same amount of liquid, are dosed with the same dropper, and are shaken with matching amplitude and direction.

Scientific and Causal Correctness rubric:
level_1: Neither tube shows any foam; or the foam in both tubes looks identical in height and duration; or foam forms only in tube A (hard water) and not in tube B; or the foam in both tubes collapses instantly; or the liquid changes color instead of foaming, in a way that doesn't match the soap-and-hardness reaction.
level_2: Foam appears in only one tube, but it is the wrong one showing abundant foam (e.g., tube A/hard water foams heavily); or foam appears in both tubes at the same time with the same height and the same collapse timing, showing no hardness-driven difference between them.
level_3: Foam appears in both tubes; the foam in tube B (soft water) is still visibly present at the end of the video; the foam in tube A (hard water) either never forms, forms only a thin single-bubble layer, or collapses completely before the video ends. This hardness-driven contrast is the core result and holds throughout.
level_4: All conditions for the 3-score level are met, and in addition: tube B's foam stays continuous and covers at least half the visible tube height for at least 2 seconds of video time; tube A never shows a foam layer thicker than a single bubble, and whatever foam does appear in tube A is gone well before the clip ends.
level_5: All conditions for the 4-score level are met, and in addition: no foam residue, film, or scattered micro-bubbles remain in tube A once its foam is gone; tube B's foam stays an even, unbroken layer with no visible drainage lines or partial collapse for as long as tube B remains on screen.

Spatiotemporal Consistency rubric:
level_1: One of the tubes vanishes from the shot and reappears moments later; the lighting or shadow on only one tube changes suddenly while the other stays the same; tube A swaps from left to right (or vice versa) with no visible movement getting it there; the liquid level in either tube jumps with no addition event; or the shaking motion starts or stops instantly with no build-up or slow-down.
level_2: Both tubes stay in place, but one rotates or tilts while the other stays upright; the shaking motion is missing frames (jerky, with gaps); the shadow cast by a tube switches sides between frames; or background elements flicker or warp.
level_3: Both tubes keep a stable position, tilt, and size throughout; the shaking motion is smooth and continuous for both tubes; the light source's direction and brightness stay the same from start to finish; neither tube clips through anything, warps, or tears apart.
level_4: All conditions for the 3-score level are met, and in addition: the side-by-side, left/right order of the tubes never drifts or shifts with the camera; the rims and liquid surface of each tube line up consistently frame to frame; no sudden brightness or contrast change makes the foam hard to see.
level_5: All conditions for the 4-score level are met, and in addition: during shaking, each tube's base moves less than its top, matching how a hand-held tube actually moves; the liquid surface's oscillation settles down naturally rather than staying constant or stopping abruptly; the foam's texture changes smoothly over time rather than popping in or out of existence.