Domain: Natural Science — Physics
Target concept: Nitrogen Dioxide Gas Diffusion Experiment

Video generation prompt: Place two wide-mouthed bottles vertically on the table, with their mouths facing each other; the mouths are separated by a card. The lower bottle has its mouth upward and contains reddish-brown nitrogen dioxide gas, while the upper bottle is inverted with its mouth downward and contains colorless, transparent air. The mouths of the two bottles are aligned. Then, remove the card separating the mouths.

Evaluation guide:
(i) Target concept: Spontaneous intermingling of gases via random thermal motion, independent of gravitational settling.
Minimum mechanism: Gas molecules must possess kinetic energy enabling random walk; container interface must be unobstructed post-removal; no external flow or pressure gradient driving motion; color contrast must be sufficient to resolve migration direction.
(ii)Storyline: Phase 1 (Pre-removal): Two static bottles: lower filled with opaque reddish-brown medium, upper fully transparent, mouths aligned and card-sealed. Phase 2 (Removal): Card fully withdrawn without disturbing bottles; no gas motion yet. Phase 3 (Diffusion onset): Reddish-brown medium begins entering upper bottle at mouth interface. Phase 4 (Progressive filling): Color advances upward in upper bottle with soft, advancing front; lower bottle color volume recedes gradually. Phase 5 (Steady mixing): Both bottles contain homogeneous reddish-brown tint, no residual sharp separation. Perspective: Fixed frontal view, centered on mouth interface; no occlusion; lighting uniform to preserve color fidelity.

Manual:
Experimental Procedure
1. Place two identical wide-mouthed glass bottles vertically: lower bottle mouth-up, upper bottle inverted (mouth-down); align mouths directly opposite each other, separated by a thin opaque card.
2. Ensure lower bottle contains reddish-brown nitrogen dioxide gas; upper bottle contains colorless, transparent air.
3. Remove the card completely to allow contact between mouths.
Observation of Experimental Phenomena
Reddish-brown gas flows upward from the lower bottle into the upper bottle; upper bottle gradually becomes reddish-brown while lower bottle remains partially filled; no abrupt boundary or mixing layer forms.
Summary of Experimental Principles
Nitrogen dioxide gas diffuses upward due to random molecular motion, not buoyancy — demonstrating that gases mix spontaneously regardless of density differences, confirming kinetic molecular theory.

Prompt Grounding rubric:
level_1: The two wide-mouthed bottles are missing, or only one appears; the bottles are not held vertically; their mouths do not face each other; the separating card between the mouths is absent; the lower bottle is not mouth-up with visible gas inside it; the upper bottle is not inverted mouth-down; the two mouths are not aligned with each other; or the card is never shown being pulled away.
level_2: Both bottles are present and upright, but at least one setup detail is wrong: the mouths face away from each other rather than toward each other; the card is missing or sits somewhere other than between the two mouths; the lower bottle is not mouth-up; the upper bottle is not inverted; the mouths are offset rather than aligned; or the card-removal action is missing or applied to the wrong object.
level_3: Both bottles stand vertically with mouths facing and aligned with each other; a card is visibly wedged between the two mouths; the lower bottle sits mouth-up and visibly holds a gas; the upper bottle sits inverted (mouth-down) and looks empty/see-through; the card is shown being pulled out.
level_4: Building on everything required at the 3-point level, the gas in the lower bottle reads as a distinct reddish-brown (not grey, black, yellow, or colorless); the upper bottle stays fully clear and colorless before removal; the card comes out in one continuous pull, without being pushed back in or hesitating partway.
level_5: Building on everything required at the 4-point level, both bottles stay put in their vertical position the entire time; the card fully clears the gap between the mouths before any gas is seen moving; no hand, label, or shadow blocks the view of the mouth-to-mouth junction during or right after the card is pulled out.

Scientific and Causal Correctness rubric:
level_1: No spreading of color between bottles ever happens; the gas stays entirely inside the lower bottle; or the reddish-brown color creeps upward while staying confined to the lower bottle without crossing into the upper bottle; or the upper bottle instead fills with an unrelated color (white haze, blue, or green); or the reddish-brown coloring simply fades away rather than moving.
level_2: Reddish-brown coloring is visible in the lower bottle, but it never visibly advances toward the upper bottle; or it advances sideways/downward instead of upward into the upper bottle; or the upper bottle turns into a uniform fog/haze rather than showing the gas's own reddish-brown tint; or the upper bottle already shows color before the card is fully removed.
level_3: After the card is removed, reddish-brown coloring is seen moving upward from the lower bottle into the upper one; the upper bottle changes from clear to partly reddish-brown; the lower bottle still shows some remaining reddish-brown color; the coloring's net direction of travel is upward, against gravity, from the denser gas into the lighter air above it.
level_4: Building on everything required at the 3-point level, the coloring spreads in a continuous, gradual way rather than jumping suddenly; the upper bottle's tint builds up bit by bit rather than appearing all at once; the lower bottle's reddish-brown visibly lightens over the same stretch of time rather than emptying out abruptly; no sharp horizontal line or layered banding appears where the two gases meet.
level_5: Building on everything required at the 4-point level, by the later part of the clip both bottles show a similarly lighter reddish-brown tint than the lower bottle's original color (consistent with the same amount of colored gas now spread across roughly twice the space), while the hue itself stays reddish-brown throughout and never shifts toward an unrelated color; the boundary between the more-colored and less-colored regions stays soft and blurred rather than forming a crisp edge.

Spatiotemporal Consistency rubric:
level_1: A bottle jumps to a different spot, size, or shape between frames; the card vanishes without ever being seen sliding out; the lighting flashes, flickers, or a shadow sweeps across the scene with no clear cause; a bottle's glass appears to warp or melt; or the background changes without any visible transition.
level_2: One clear break in continuity shows up: a bottle shifts position between shots with nothing shown causing it; the card is present in one moment and simply gone the next, with no visible slide-out motion; the light falling on the bottles changes in a sudden step rather than gradually; or the mouth-to-mouth alignment breaks partway through the clip (a bottle tilts or drifts sideways).
level_3: Both bottles stay fixed in place and orientation for the whole clip; the card's motion from inserted to fully out is smooth with no jump; neither bottle's glass shows unnatural stretching or warping; the direction and strength of the light on the bottles, and the shadows they cast, stay the same from first frame to last.
level_4: Building on everything required at the 3-point level, the card's withdrawal moves at a steady, even pace with no jerks, stutters, or sudden bursts of speed; there's no visible frame skip or repeat that would cause a stutter; if a hand is pulling the card, it stays logically in front of or behind the bottles the whole time rather than popping between the two.
level_5: Building on everything required at the 4-point level, the circular mouths of both bottles keep a true round shape with no perspective skew that would throw off how aligned they look; the camera's viewpoint never blurs or blocks the mouth-to-mouth junction in a way that hides the diffusion boundary; every motion in the clip (the card being pulled, the coloring spreading) looks physically continuous from the same fixed camera angle.