Domain: Engineering — Food and Bioprocess Engineering
Target concept: Comparison of the Reaction Rate between Diluted Vinegar and Undiluted Vinegar (Vinegar-Sodium Bicarbonate Reaction)

Video generation prompt: Two identical transparent cups are placed side by side: the left cup contains undiluted vinegar, and the right cup contains diluted vinegar. An equal amount of one tablespoon of baking soda is added to both cups simultaneously.

Evaluation guide:
(i) Target concept: Reaction kinetics dependence on reactant concentration in acid-base gas-evolution reactions.
Minimum mechanism: Acetic acid must be present in aqueous solution; sodium bicarbonate must be solid-phase; CO₂ gas generation must drive foam formation; higher [H⁺] accelerates HCO₃⁻ decomposition; dilution reduces collision frequency between H⁺ and HCO₃⁻ ions.
(ii)Storyline: Frame 0–1: Static wide shot showing two identical transparent cups side-by-side, left filled with amber-tinted liquid (undiluted vinegar), right with paler liquid (diluted vinegar). Frame 2–3: Hand enters with tablespoon holding compact mound of white granular baking soda. Frame 4: Spoon positioned equidistant above both cup openings. Frame 5: Simultaneous downward motion deposits equal powder into both cups. Frame 6–8: Bubbling initiates immediately in left cup; visible delay (~0.3s) before onset in right cup. Frame 7–9: Foam in left cup rises rapidly to dominant height and sustains; foam in right cup rises slower, peaks lower, and begins collapsing while left foam remains intact. Frame 10: Final state shows left cup with tall, stable foam dome; right cup with diminished, fragmented foam. Viewpoint: Fixed frontal, eye-level, full-cup framing; no occlusion; consistent lighting; no camera motion.

Manual:
Experimental Procedure
1. Place two identical transparent cups side-by-side on a flat surface.
2. Fill left cup with undiluted vinegar; fill right cup with diluted vinegar (e.g., 1:3 vinegar:water).
3. Using one tablespoon, simultaneously add baking soda to both cups.
Observation of Experimental Phenomena
- Left cup produces taller, longer-lasting white foam with denser bubbling.
- Right cup produces shorter, faster-collapsing white foam with sparser bubbling.
- No color change, precipitation, or overflow in either cup.
Summary of Experimental Principles
Undiluted vinegar has higher acetic acid concentration → faster reaction rate with sodium bicarbonate → more rapid CO₂ gas production → greater foam volume and persistence.

Prompt Grounding rubric:
level_1: No two transparent cups visible; or only one cup present; or cups not side-by-side; or vinegar not present in left cup; or diluted vinegar not present in right cup; or baking soda not added; or addition not simultaneous; or no tablespoon-sized quantity implied (e.g., spoon absent, powder poured from container without spoon, or spoon used but no visible scoop action)
level_2: Two transparent cups present and side-by-side, but at least one of the following is missing/incorrect: left cup contains non-vinegar liquid (e.g., water, juice) or no liquid; right cup contains undiluted vinegar or no liquid; baking soda is added but not with a spoon; spoon is present but no visible transfer of powder into either cup; addition occurs sequentially (left then right or vice versa), not simultaneous
level_3: Two identical transparent cups placed side-by-side in same frame; left cup contains clear liquid labeled or visually consistent with undiluted vinegar (e.g., amber-tinted, no dilution cues); right cup contains clear liquid with visible dilution cue (e.g., lighter tint, labeled “diluted”, or shown being mixed with water earlier in video); one tablespoon of white granular baking soda is scooped with a spoon and delivered to both cups; delivery appears synchronous (spoon enters frame near both cups at same time or two spoons used identically and simultaneously)
level_4: All conditions for score 3 met, AND: both cups are identical in shape/size/transparency; spoon is same size and type for both deliveries; baking soda quantity is visibly equal (same mound volume, same spoon fill level); liquid levels in both cups are approximately equal before addition; no extraneous objects occluding cups or spoon during addition
level_5: All conditions for score 4 met, AND: left cup liquid has deeper amber hue than right cup liquid; right cup liquid shows subtle meniscus or clarity cue indicating lower solute concentration (e.g., no sediment, sharper edge refraction); spoon delivers baking soda in single continuous motion to both cups without pause, retraction, or adjustment; both cups remain fully stationary and unobstructed throughout entire event; viewpoint is fixed frontal orthographic (no parallax shift, no zoom, no rotation)

Scientific and Causal Correctness rubric:
level_1: No reaction observed in either cup; or reaction occurs identically in both cups (same bubble intensity, same duration, same foam height); or foam appears in only one cup; or foam is colored, opaque, or non-white; or liquid changes color in either cup; or solid residue remains visible after reaction ceases
level_2: Reaction occurs in both cups, but at least one of the following is violated: bubbles appear simultaneously in both cups; foam rises to same maximum height in both cups; foam collapses at same rate; foam is not white and opaque; foam does not originate from liquid surface; no visible difference in bubble density or foam volume between cups
level_3: Reaction occurs in both cups with visible bubbling; foam appears in both cups; foam in left cup is taller than foam in right cup; foam in left cup persists longer than foam in right cup; foam is white and opaque in both cups; bubbles originate at liquid–powder interface in both cups; no color change or precipitation observed in either cup
level_4: All conditions for score 3 met, AND: bubble formation in left cup begins before or at same instant as in right cup; foam in left cup reaches peak height earlier than in right cup; foam in left cup maintains structural integrity (continuous froth) while foam in right cup shows earlier thinning or collapse at top layer; no splashing, overflow, or spillage in either cup
level_5: All conditions for score 4 met, AND: bubble nucleation in left cup is denser and more rapid than in right cup; foam in left cup forms a stable, cohesive dome exceeding foam height in right cup by a clearly discernible margin (not subtle); foam in right cup visibly recedes within 1 second of peak while left cup foam remains intact for ≥2 seconds longer; no discontinuity in bubble generation in left cup (continuous stream vs. intermittent bursts in right cup)

Spatiotemporal Consistency rubric:
level_1: The two cups jump to a different position between frames with no visible movement between them; or the spoon appears in a new place with no visible motion path getting it there; or the liquid level in either cup suddenly rises or falls with no cause; or the lighting suddenly flashes or a shadow sweeps across the scene; or a cup flickers between transparent and opaque; or the tabletop or background suddenly warps or rotates.
level_2: One clear spatiotemporal break occurs: the spoon disappears mid-motion and reappears elsewhere; a cup shifts sideways by more than its own width between consecutive frames; the foam appears already fully formed with no visible growth phase; the liquid surface bends upward unnaturally while bubbling; or the reflections on a cup's walls don't match what a fixed, unmoving camera would show.
level_3: Both cups stay in the same place and orientation throughout; the spoon's motion is a smooth, continuous arc with no floating or sudden reversal; the foam in each cup grows upward from the liquid surface without spreading sideways or sinking back down; there are no sudden lighting changes; reflections on the cup walls stay consistent with a static camera; the spoon never appears to pass through a cup wall.
level_4: All 3-point conditions hold, and additionally: the spoon moves at a steady speed while delivering the baking soda to each cup; the foam in each cup rises smoothly and continuously with no stutter, pause, or momentary shrinking before its peak; the liquid surface in each cup stays flat and still before the baking soda is added, deforming only where bubbles form; the cup rims and tabletop line up consistently from frame to frame.
level_5: All 4-point conditions hold, and additionally: no frame is duplicated or shows ghosting of the cups, spoon, or foam; motion blur on the spoon and on the rising foam looks consistent with how fast each is actually moving; the bubbles don't strobe or flicker unnaturally between frames; the highlights on both cups shift together as if lit by one consistent light source; the tabletop looks flat and level in every frame, with no visible warping, buckling, or tilt.