Domain: Engineering — Mechanical Engineering
Target concept: Three-Point Bending Test: Metal Bar vs. Plastic Strip vs. Ceramic Plate

Video generation prompt: A three-point bending device with two support points and a central loading head applies gradually increasing downward loads to metal rods, plastic bars, and ceramic tiles in sequence.

Evaluation guide:
(i) Target concept: Mechanical response divergence under identical three-point bending loading across material classes.
Minimum mechanism: Applied downward load at center induces tensile stress on bottom surface and compressive stress on top; failure mode depends on intrinsic material properties (yield strength, fracture toughness, elastic modulus, dislocation mobility).
(ii)Storyline: 1. Fixed-view shot establishes full three-point bending apparatus (two supports + central loading head) with metal rod centered. 2. Loading head descends vertically → metal rod develops smooth, symmetrical curvature (no fracture). 3. Metal rod is removed; plastic bar is placed identically → loading head descends → bar curves more deeply and retains bend after unloading (if shown) or shows clear yielding onset. 4. Plastic bar is removed; ceramic tile is placed identically → loading head descends → tile develops radial crack from center, then fragments. 5. All transitions preserve fixed camera position, consistent lighting, and identical spatial registration of supports/loading head; no material appears outside its designated test phase.

Manual:
Experimental Procedure: Place metal rod across two fixed supports; lower central loading head until visible bending occurs. Replace with plastic bar; repeat loading until permanent bend forms. Replace with ceramic tile; apply load until fracture occurs.
Observation of Experimental Phenomena: Metal rod bends elastically (curves smoothly, returns when unloaded). Plastic bar bends more severely and retains curvature after unloading. Ceramic tile shows sudden crack formation and fragmentation under load.
Summary of Experimental Principles: Three-point bending tests flexural rigidity and failure modes: metals exhibit ductile elastic-plastic behavior, plastics show viscoelastic yielding, ceramics demonstrate brittle fracture due to low tensile strength and absence of dislocation mobility.

Prompt Grounding rubric:
level_1: No three-point bending apparatus is visible: no support points and no central loading head appear, and none of the three test materials (metal rod, plastic bar, ceramic tile) can be identified anywhere in the frame.
level_2: At least one of the three materials appears somewhere in the frame, but the two support points and the central loading head are not clearly identifiable as a bending apparatus, and there is no indication that materials are being tested one after another.
level_3: A three-point bending apparatus is visible with two clear support points and one central loading head, and all three materials (metal rod, plastic bar, ceramic tile) appear somewhere in the video, but they are not shown in a clean one-at-a-time sequence (e.g., two materials are visible together, or the order in which they are tested is unclear).
level_4: The three-point bending apparatus is fully visible with two support points and one central loading head; the metal rod, plastic bar, and ceramic tile each appear individually, one after the other, each centered between the supports and directly under the loading head, with no two materials present in the frame at the same time.
level_5: The three-point bending apparatus is fully visible with two support points and one central loading head; the metal rod, plastic bar, and ceramic tile appear strictly in that order with no repetition, skipping, or overlap, each placed identically centered between the supports and directly beneath the loading head, and no other object enters the frame during any of the three tests.

Scientific and Causal Correctness rubric:
level_1: None of the three materials shows any deformation or failure during loading: the metal rod, plastic bar, and ceramic tile all stay visually rigid and unchanged in shape, and there is no visible difference in how the three materials respond to the same loading action.
level_2: At least one material's response contradicts known mechanical behavior; e.g., the ceramic tile bends smoothly like a ductile metal without ever cracking, the metal rod fractures suddenly like a brittle material, or the plastic bar snaps instantly instead of bending, so the loading action and the observed deformation are not causally linked in a physically sensible way.
level_3: Each material shows a distinct, generally plausible response: the metal rod bends into a smooth curve without breaking, the plastic bar curves noticeably more than the metal rod and appears to hold some of that curve, and the ceramic tile cracks or breaks apart under load; but the timing or clarity of these responses is inconsistent across materials, for example the ceramic tile appears to crack before the loading head has visibly touched it, or the plastic bar's extra curvature relative to the metal rod is hard to distinguish.
level_4: The metal rod bends smoothly into a continuous curve with no fracture; the plastic bar curves noticeably more than the metal rod did and shows a bend that persists once the load eases, going visibly further than the metal did; the ceramic tile develops a sudden, localized crack or shatters; each material's deformation is visible only while the loading head is actively pressing down on it, with no phenomenon appearing before or after loading.
level_5: The metal rod's curve tracks the loading head's descent and would relax back toward straight if the load were removed; the plastic bar's bend clearly exceeds the metal rod's and remains after the load eases, showing it went past its elastic limit; the ceramic tile fractures abruptly with a visible crack that separates fragments, and does so only under load; each material shows only its own characteristic response: the metal rod never cracks like the ceramic, the ceramic never bends smoothly like the metal, and the plastic bar's behavior is never confused with either.

Spatiotemporal Consistency rubric:
level_1: Severe discontinuity: a material appears to teleport into position instead of being placed, the loading head jumps to a new height without visible motion, a support point vanishes and then reappears, lighting or shadows shift abruptly between the three tests, or the footage cuts and skips in a way that breaks the sense of one continuous test sequence.
level_2: At least two of the following occur: a material's position shifts without a visible placement motion, the loading head moves along a path that is not straight and vertical, a support point changes location partway through, the background flickers or warps, or the motion during a test looks jerky or freezes momentarily.
level_3: One small discontinuity is visible (such as a brief cut when switching between materials, or a moment of camera shake during a transition), but the support points and loading head otherwise stay in the same place relative to each other across all three tests, the loading head's descent is vertical and continuous during each test, and no material vanishes or appears without a visible placement action.
level_4: The two support points stay in the same location for the entire video; the loading head descends in a continuous, vertical motion during each of the three tests; each material is placed into and removed from position with a visible, continuous motion rather than an abrupt substitution; the apparatus's lighting does not shift abruptly when one material is swapped for the next.
level_5: The camera viewpoint never pans, tilts, or zooms for the entire sequence; the loading head's descent is smooth and continuous in each of the three tests with no sudden speed changes; the support points never shift location; switching from one material to the next is shown as a continuous placement action (e.g., a hand setting the next piece down) rather than a cut or substitution, so the scene reads as one unbroken continuous test sequence from start to finish.