Domain: Engineering — Energy Engineering
Target concept: Carbon neutrality: Flue gas from coal-fired boilers rapidly makes lime water turbid with high turbidity, while natural gas flue gas causes slower and milder turbidity, reflecting the difference in carbon emissions.

Video generation prompt: Two identical small boilers are shown in the same scene, with the boiler on the left burning natural gas and the boiler on the right burning coal. The exhaust gases from both boilers are introduced into test tubes containing clear lime water, and the rate and extent of turbidity in the solutions in the two test tubes are compared.

Evaluation guide:
(i) Target concept: Differential CO₂ emission rates between coal and natural gas combustion, measured via lime water turbidity kinetics.
Minimum mechanism: CO₂ must be generated in flue gas; lime water must be freshly prepared saturated Ca(OH)₂ solution; reaction Ca(OH)₂ + CO₂ → CaCO₃↓ + H₂O must proceed to form visible suspended precipitate; turbidity magnitude correlates with CO₂ partial pressure and exposure time.
(ii)Storyline: Frame opens on static wide shot showing two identical boilers side-by-side (left: natural gas, right: coal), each linked by straight, unoccluded exhaust pipe to an upright glass test tube containing transparent lime water. At t=0, both boilers emit visible thermal output (e.g., faint blue flame for NG, orange-yellow for coal; or uniform steam plumes if flame obscured). Gas flows continuously through pipes into tubes. Turbidity emerges first in right tube, then later in left tube; right tube progresses to full milky opacity while left tube remains semi-transparent. Entire sequence viewed from fixed frontal angle with no cuts, zooms, or pans; all objects remain fully visible and spatially stable.

Manual:
Experimental Procedure
1. Place two identical small boilers side-by-side in same scene: left labeled natural gas, right labeled coal.
2. Connect exhaust outlet of each boiler to a separate upright test tube containing clear lime water.
3. Activate both boilers simultaneously.
Observation of Experimental Phenomena
- Right test tube (coal) becomes turbid faster and reaches greater opacity than left test tube (natural gas).
- Both tubes start fully transparent and colorless; turbidity appears only after gas exposure.
Summary of Experimental Principles
Coal combustion produces more CO₂ than natural gas combustion; CO₂ reacts with Ca(OH)₂ in lime water to form insoluble CaCO₃ precipitate, causing turbidity. Higher CO₂ concentration → faster/more intense turbidity.

Prompt Grounding rubric:
level_1: Fewer than two boilers appear on screen, or no lime-water test tube (or only one) is shown; the two boilers cannot be told apart by any physical cue such as flame color, glow, exhaust color, relative size, or visible fuel feed (coal chute versus gas line); or an exhaust pipe from a boiler is missing or is clearly not connected to any test tube.
level_2: Both boilers and both lime-water test tubes are present, but at least one link in the setup is broken: an exhaust pipe does not visibly run from its boiler to its matching test tube, one of the two lime-water tubes is not clearly visible at the start of the video, or the pairing between a given boiler and its test tube is ambiguous (unclear which pipe feeds which tube).
level_3: Two boilers that can be told apart by fuel type (natural gas on the left, coal on the right, shown through cues like flame color, exhaust color, or fuel feed) each connect through an unbroken exhaust pipe to its own upright test tube of clear lime water, with boiler, pipe, and tube correctly grouped as one unit on each side so the two setups can be directly compared.
level_4: Everything described for the 3-point setup holds, and in addition: both exhaust pipes remain fully visible from boiler outlet to tube inlet with no gap, occlusion, or visible seam; the two test tubes match each other in size and both stand upright; and no on-screen caption, arrow, or graphic overlay is needed to identify the boilers, pipes, or tubes.
level_5: Everything described for the 4-point setup holds, and in addition: the camera keeps one fixed frontal framing with both boilers and both test tubes fully visible for the entire video, without any cut, pan, or zoom; and both boilers show a visible sign of being lit and running (flame color, glowing firebox, or steam/exhaust plume) rather than sitting inert.

Scientific and Causal Correctness rubric:
level_1: Neither test tube ever becomes turbid; or both tubes become turbid at the same time and to the same degree with no visible difference between them; or the coal (right) tube's turbidity appears later than the natural-gas (left) tube's; or either lime-water sample already looks colored (e.g., blue, yellow, or green) before any gas is introduced.
level_2: Turbidity shows up in only one of the two test tubes while the other stays clear for the whole video; or turbidity appears in both tubes but starts and progresses at visually indistinguishable rates; or a tube's lime water already looks cloudy before its exhaust gas has reached it.
level_3: Both lime-water samples start out clear and colorless, and both eventually turn turbid, with the coal (right) tube's cloudiness starting earlier and/or looking denser and whiter than the natural-gas (left) tube's cloudiness at matching points in the video.
level_4: Everything described for the 3-point comparison holds, and in addition: once turbidity starts in the coal tube it keeps increasing without clearing up, flickering, or reversing; no cloudiness appears before exhaust gas has actually reached a tube; and at every point you can check across the video, the coal tube's turbidity is visibly ahead of the natural-gas tube's.
level_5: Everything described for the 4-point comparison holds, and in addition: by the video's end the coal tube looks fully milky white and opaque while the natural-gas tube is still clearly translucent enough to see through, so the two tubes are never at the same turbidity level in any frame; and in each tube the cloudiness spreads as an even column through the liquid rather than as floating clumps or a sideways streak.

Spatiotemporal Consistency rubric:
level_1: The natural-gas boiler (left), the coal boiler (right), an exhaust pipe, or a lime-water test tube disappears from the frame or appears out of nowhere partway through the video; the natural-gas and coal boilers swap left/right sides, or either boiler or tube jumps to a different position on screen, breaking the established left-natural-gas / right-coal layout; an exhaust pipe separates from its boiler or tube and reconnects on its own; or the scene's overall lighting swaps abruptly, such as switching from day to night, partway through.
level_2: One test tube is hidden from view for a long stretch, roughly a third of the video or more, and then becomes visible again; a visible gap or mismatched seam appears where a pipe meets a boiler or tube; or the flame or exhaust color that distinguishes the two boilers changes partway through with no visible cause, such as the left (natural-gas) boiler's blue flame turning orange-yellow like the coal boiler's flame, or the reverse.
level_3: Both boilers, both exhaust pipes, and both test tubes each stay in the same screen position for the whole video; the exhaust pipes stay intact and connected end to end throughout; no boiler or tube cracks, bends unnaturally, or breaks apart; and any visible steam or vapor moves smoothly and plausibly rather than jumping or freezing in place.
level_4: Everything described for the 3-point scene holds, and in addition: neither test tube nor boiler visibly shakes or flickers on screen; the boilers and tubes keep their proper proportions with no visible warping or stretching; and any steam or vapor plume flows as one continuous stream from boiler outlet into pipe rather than cutting in and out.
level_5: Everything described for the 4-point scene holds, and in addition: the video shows no frames that look dropped or repeated and no motion blur that looks wrong for how fast anything, such as steam or gas flow, appears to move; the outlines of the boilers, pipes, and tubes stay clean and steady rather than flickering or shimmering; and the boilers hold their position relative to the background with no drifting or sliding while the camera holds its shot.