Domain: Natural Science — Chemistry
Target concept: Methane Combustion

Video generation prompt: A tube discharges colorless methane gas; an ignition source is brought toward the tube outlet.

Evaluation guide:
(i) Target concept: Sustained, localized ignition of invisible gaseous fuel at a fixed orifice, producing a thermally stable, chemically characteristic flame.
Minimum mechanism: Gas must be optically transparent under ambient lab lighting; ignition must occur *at* the orifice (not upstream/downstream); flame must emerge *only* upon ignition and persist *only* while gas flows; flame color zoning must reflect hydrocarbon combustion physics (blue inner cone + luminous outer tip).
(ii)Storyline: Frame 1–3: Static shot showing upright tube with no visible emission. Frame 4–6: Continuous, transparent gas effusion begins from tube outlet (no visual medium). Frame 7–8: Ignition source approaches and contacts tube outlet. Frame 9–10: Flame appears *exclusively* at tube outlet (no delay, no offset, no detachment) with immediate blue+yellow-orange structure. Perspective is fixed frontal/slightly angled; tube occupies consistent screen region; flame never occludes tube outlet; background remains static and non-distracting.

Manual:
Experimental Procedure
1. A rigid cylindrical tube is held vertically. 
2. Colorless methane gas flows steadily from the tube outlet. 
3. A flame source (e.g., lighter or match) is brought into contact with the gas at the tube outlet.
Observation of Experimental Phenomena
- Methane gas is invisible during discharge (no mist, fog, or color). 
- Upon ignition, a steady flame appears instantly and continuously at the tube outlet. 
- The flame has a blue lower region and a bright yellow-orange luminous tip.
Summary of Experimental Principles
Methane (CH₄) undergoes complete combustion in air: CH₄ + 2O₂ → CO₂ + 2H₂O + heat/light. The blue base indicates hot, efficient combustion; the yellow-orange tip results from incandescent carbon particles formed under slightly fuel-rich conditions at the flame periphery.

Prompt Grounding rubric:
level_1: No tube is shown discharging any gas, no ignition action is depicted, and no flame appears at any point; none of the prompt's elements (tube, gas discharge, ignition) are established.
level_2: A tube is present and emits a substance, but the substance is visibly not colorless (e.g., a white mist, smoke trail, or tinted vapor is shown); or an ignition action occurs with no gas discharge shown beforehand; or a flame appears with no ignition source or tube visible near it.
level_3: The tube visibly discharges a colorless gas (no fog, mist, or haze trailing from the outlet), an ignition source is brought toward the tube outlet, and a flame appears; but the flame's position relative to the outlet is ambiguous (e.g., it looks detached from the tube or floating slightly away from it), or it is unclear whether the flame's appearance is actually triggered by the ignition action shown.
level_4: The tube discharges a clearly colorless gas (transparent, with no condensation or particulate trace); the ignition source makes contact at the tube outlet; the flame appears continuously at the outlet immediately after the ignition action, staying anchored there with no floating or drifting; the tube, gas discharge, and flame are all shown in the same spatial region in the correct order (gas first, then ignition, then flame).
level_5: All conditions for score 4 are met, and additionally: the tube keeps a consistent rigid, cylindrical shape and diameter throughout; the gas discharge shows no odd visual artifacts (pulsing, distortion, unnatural shimmer); the ignition action is unambiguous (a visible flame or spark clearly touching the outlet); the flame stays continuously attached to the outlet with no unexplained flicker-outs or positional drift across the sequence.

Scientific and Causal Correctness rubric:
level_1: No flame appears at all; or a flame appears with no gas discharge or ignition shown beforehand; or the flame burns in a color inconsistent with hydrocarbon combustion (e.g., entirely green, purple, or deep red), suggesting contamination or a non-methane fuel.
level_2: The flame is present but burns uniformly blue with no luminous yellow-orange region at all (suggesting an unrealistically complete premix rather than a simple diffusion flame); or the flame appears before the ignition source ever reaches the outlet, or it keeps burning well after the gas discharge has visibly stopped.
level_3: The flame at the tube outlet shows both a blue base and a yellow-orange luminous tip, matching methane's characteristic diffusion-flame appearance, but the yellow-orange portion is intermittent, partly hidden, or unevenly shaped from frame to frame.
level_4: The flame consistently shows a blue lower region joined to a distinct, continuous yellow-orange upper region for the whole time it burns; no smoke, soot, popping, or premature extinguishing appears.
level_5: All conditions for score 4 are met, and additionally: the flame's overall size stays steady with no sudden collapse or flare-up; the blue-to-yellow-orange zoning stays sharp and contiguous with no blurring or inversion between the two zones; no effects inconsistent with clean methane combustion appear (no black smoke, no soot residue, no sputtering); the flame keeps burning steadily for as long as gas is flowing and only goes out once the gas discharge visibly ends.

Spatiotemporal Consistency rubric:
level_1: The tube's position or apparent size changes abruptly between one frame and the next with no motion bridging the change, as if two separate shots had been spliced together; the flame appears at a spot clearly detached from the tube outlet with no visible path connecting them; the gas discharge switches from absent to fully established within a single frame with no gradual buildup; or the scene's lighting flashes or blacks out abruptly between frames with no visible source causing it.
level_2: The tube shows a slight unexplained shift in position, or a subtle bend or warp, between frames despite being rigid; the flame's attachment point along the outlet drifts sideways by more than roughly one tube-width over the sequence instead of staying put; the glow the flame casts on the nearby tube surface changes brightness or color erratically with no clear cause.
level_3: The tube stays rigid and in the same screen position throughout; the flame stays anchored at the outlet, its tip flickering only in the small, non-directional way real open flames do; where a faint heat-shimmer from the gas is visible, it flows continuously without stutter-stepping; no part of the tube or flame clips, tears, or momentarily vanishes.
level_4: All conditions for score 3 are met, and additionally: the flame grows from ignition to its full size over a brief, visible interval rather than snapping instantly to full size; the tube shows no rotation, tilt, or scale change across the sequence; the camera's framing stays fixed with no zoom, pan, or roll.
level_5: All conditions for score 4 are met, and additionally: the flame's flicker, its blue-to-yellow-orange color transition, and its edge softness all change smoothly frame to frame with no sudden jump in shape or brightness; the glow the flame casts on the tube surface changes in step with the flame itself rather than independently of it; no frame shows visible strobing, doubled edges, or a frozen/duplicated frame.