Domain: Engineering — Materials Science & Engineering
Target concept: Ignite the cotton fiber and confirm that it burns rapidly, leaving only a white fine ash without any black residue.

Video generation prompt: Use tweezers to grasp a small piece of cotton fiber. Bring it near a flame to ignite it, and allow the cotton fiber to burn freely in the air. After ignition, let it burn completely, then use the tweezers to remove the remaining solid residue and place it on a surface.

Evaluation guide:
(i) Target concept: Cellulose-specific combustion behavior under atmospheric conditions.
Minimum mechanism: Complete oxidative pyrolysis of anhydrous glucose units in cellulose chains, yielding volatile gases and non-volatile alkaline earth metal oxides as the sole solid residue, requiring sufficient oxygen, no contamination, and full burn-through.
(ii)Storyline: [Frame 0–2] Tweezers close on fluffy white cotton fiber → [Frame 3–4] Fiber approaches flame, tip contacts flame → [Frame 5] Instant ignition at contact point with visible glow → [Frame 6–7] Flame propagates uniformly; fiber shrinks, glows, and vanishes → [Frame 8] Only white fine ash remains in original position → [Frame 9] Tweezers lift ash intact → [Frame 10] Ash placed centrally on surface with no dispersion. Perspective: Fixed frontal close-up (tweezers + fiber + flame + surface all simultaneously visible); visibility: No occlusion at any stage; all transitions are causally linked and temporally contiguous.

Manual:
Experimental Procedure
1. Use tweezers to grasp a small piece of white cotton fiber.
2. Bring the fiber near an open flame and ignite it at the tip.
3. Allow the fiber to burn freely in air without support or airflow.
4. After complete combustion, use tweezers to retrieve the remaining solid residue.
5. Place the residue on a flat, neutral-colored surface.
Observation of Experimental Phenomena
- Cotton ignites instantly upon flame contact.
- Burns rapidly with a yellow-orange flame, no smoke or melt.
- Disappears completely except for a small pile of white, fine, powdery ash.
- Zero black residue, char, or fibrous remnants visible.
Summary of Experimental Principles
Cotton is pure cellulose; combustion yields CO₂, H₂O vapor, and mineral ash (mainly calcium/magnesium oxides), producing only white fine ash when burned completely in air.

Prompt Grounding rubric:
level_1: No cotton fiber visible; no tweezers present; no flame or ignition event; no residue placement observed; none of the posted_prompt steps (grasp, bring near flame, ignite, burn freely, remove residue, place on surface) occur in any form.
level_2: At least one object from the prompt is present (e.g., tweezers OR cotton fiber OR flame), but zero steps from the posted_prompt sequence are executed in correct order; no recognizable grasp-action, no flame-contact event, no residue handling.
level_3: All three core objects present (cotton fiber, tweezers, flame); grasp action with tweezers visible; cotton fiber brought near flame; ignition occurs; burning proceeds without external support (freely in air); residue is removed and placed on a surface; all steps occur in correct sequential order, but at least one core object has incorrect type (e.g., synthetic fiber instead of cotton) or incorrect state (e.g., cotton pre-charred before ignition).
level_4: All core objects correct (cotton fiber, metal tweezers, open flame); all five posted_prompt steps executed in correct order: (1) tweezers grasp small cotton fiber, (2) fiber brought near flame, (3) ignition initiates at point of flame contact, (4) fiber burns freely without support (no hand/tweezer shielding or forced airflow), (5) tweezers remove remaining solid residue and place it on a flat surface; but one non-core flaw exists (e.g., residue placement occurs off-center, minor flicker in flame, or brief occlusion of residue during placement).
level_5: All core objects correct and visually unambiguous (white fluffy cotton fiber, standard lab tweezers, steady yellow-orange flame); all five posted_prompt steps fully visible, continuous, and executed in strict sequence with no interruption, occlusion, or ambiguity; cotton fiber remains fully visible throughout ignition and burn; residue is a single, intact, white fine ash pile placed centrally on surface; no extraneous objects, motion artifacts, or temporal jumps.

Scientific and Causal Correctness rubric:
level_1: No combustion phenomenon observed; cotton fiber does not ignite; or ignites but produces thick black smoke, molten drip, charring, or large black residue, inconsistent with cotton's known behavior; no ash formation visible.
level_2: Fiber ignites but exhibits at least two scientifically invalid phenomena: e.g., sustained black residue + slow smoldering + no flame propagation; or rapid burn with bright sparks/flame color inconsistent with cellulose (e.g., green/blue flame); or ash appears gray, clumped, or granular instead of white and fine.
level_3: Cotton fiber ignites rapidly upon flame contact and sustains open flame; flame propagates fully across fiber; burning completes within observable timeframe; residue is solid and present; but residue is not exclusively white and fine ash (e.g., includes visible black specks, fused edges, or fibrous fragments), violating the knowledge point "leaving only a white fine ash without any black residue".
level_4: Fiber ignites rapidly upon flame contact; burns completely with steady yellow-orange flame; leaves only residue, and that residue is visually white, fine, powdery, and homogeneous; no black specks, no fibrous strands, no discoloration; but one minor causal inconsistency exists (e.g., flame appears to shrink *before* full burn completion, or residue disperses slightly *during* tweezers placement suggesting instability not seen in real cotton ash).
level_5: Ignition occurs instantly at flame contact point; flame spreads uniformly and rapidly across entire fiber; fiber disappears entirely except for a single, stationary, cohesive pile of residue; residue is purely white (no hue shift), uniformly fine (no texture variation or granularity), non-cohesive (no clumping), and remains intact after placement, fully matching the knowledge point: "burns rapidly, leaving only a white fine ash without any black residue".

Spatiotemporal Consistency rubric:
level_1: Severe spatiotemporal rupture: the tweezers, the cotton fiber, or the ash residue jump from one position to another with no visible path between them (for instance, the tweezers hold the unburned fiber in one instant and hold a finished ash pile somewhere else in the very next instant); the flame appears or disappears with no visible spark or extinguishing motion; the shot cuts abruptly to a different framing or background mid-action.
level_2: Multiple breaks in continuity are visible: the fiber, the tweezers, or the ash flicker, vanish, or reappear more than once; the flame's brightness jumps sharply up or down with no visible cause; the ash pile is already fully formed while the fiber is still visibly burning; the tweezers move in short unnatural jumps rather than a continuous path between grasping, igniting, and placing the residue.
level_3: One clear spatiotemporal flaw is visible: for example, the cotton fiber disappears mid-burn with no ash left in its place, or the ash appears in the shot without the tweezers having carried it there, or the flame goes out and reignites on its own with no new spark; aside from this single flaw, the tweezers, fiber, and ash keep sensible relative positions with no doubling, stretching, or warping of their shapes.
level_4: The tweezers move in one continuous path through grasping, igniting, and placing the residue; the flame's position against the shrinking, curling fiber stays physically sensible; the ash travels from the burn spot to the surface in an unbroken motion without changing size along the way; the flame's own glow stays steady rather than strobing or freezing; but one small flaw remains, such as the ash briefly looking slightly see-through just after it lands, or its edges shimmering for an instant as it settles.
level_5: No spatiotemporal flaws are visible anywhere in the clip: the tweezers travel in one continuous path from grasp to ignition to retrieval to placement; the flame flickers naturally and steadily, never freezing or strobing, as the fiber curls, shrinks, and glows away to nothing; the ash forms in place, sits undisturbed until the tweezers touch it, then moves as a single solid clump to the surface, keeping the same size and the same bright white color under the flame's glow throughout.