Domain: Engineering — Materials Science & Engineering
Target concept: Cantilever Beam Test: Comparison of Carbon Fiber and Aluminum Under the Same Suspended Load

Video generation prompt: In the laboratory, two identical cantilever beams were clamped side by side—one made of black carbon fiber and the other of silver-colored aluminum—with identical weights suspended at their respective free ends, while keeping the camera position constant.

Evaluation guide:
(i) Target concept: Elastic bending deflection of cantilever beams under static point load is inversely proportional to flexural rigidity (EI), where E is Young's modulus and I is second moment of area. Minimum mechanism: Identical geometry (I same) + identical load + linear elastic regime → deflection difference arises solely from E difference (E_cf > E_al).
(ii)Storyline: [t0–t1] Two parallel, clamped beams visible side-by-side, free ends unloaded and level. [t1–t2] Weights descend and attach to the free ends (visible motion, no teleportation). [t2–t3] Both beams bend downward continuously and settle; the carbon fiber beam maintains a visibly straighter profile than the aluminum beam; the entire sequence is observed from a fixed frontal viewpoint with consistent lighting and no occlusion of the deflection zones.

Manual:
Experimental Procedure
1. Mount two identical cantilever beams side-by-side on a rigid support, clamping them identically.
2. Attach identical weights to the free end of each beam simultaneously.
3. Hold camera position fixed; record 10 seconds of stable observation.
Observation of Experimental Phenomena
- Both beams deflect downward under load.
- The black carbon fiber beam deflects less than the silver aluminum beam.
- Deflection difference is stable, visible, and maintained throughout observation.
Summary of Experimental Principles
Carbon fiber has a higher Young's modulus (E) than aluminum. Since both beams share identical cross-sectional geometry (the same second moment of area, I), their flexural rigidity (EI) differs only because of this difference in E. Under an identical suspended load, the beam with higher EI — the carbon fiber beam — deflects less, which directly demonstrates carbon fiber's higher Young's modulus relative to aluminum in this test, not a difference in specific stiffness (stiffness-to-density ratio), since neither beam's mass nor density is measured or shown here.

Prompt Grounding rubric:
level_1: No cantilever beams are visible; or only one beam appears; or no weights are shown suspended; or the beams are not shown clamped; or the camera view is not fixed (it pans, zooms, or repositions); or the two beams' materials cannot be told apart by color (both look black, both look silver, or the color is unclear).
level_2: Both beams are present and clamped, but at least one of the following is wrong: the beams are not shown together in the same frame; the weights are not visibly hanging from the free ends; the material colors are ambiguous (carbon fiber not black, aluminum not silver); or the two beams are clamped at inconsistent locations (e.g., one at a wall mount, the other at a table edge).
level_3: Two clamped cantilever beams sit side by side within a fixed camera frame; each has an identical-looking weight visibly hanging from its free end; the carbon fiber beam is black and the aluminum beam is silver; both beams and their loaded ends stay fully visible and still during the observation period.
level_4: Everything required at the 3-point level is present, and in addition: the two beams are mounted with parallel long axes and matching vertical alignment at the clamped ends; the two weights match each other in shape and size; and neither beam's free end or mid-span is ever blocked from view.
level_5: Everything required at the 4-point level is present, and in addition: both beams share the same clamping depth and the same protruding length; both weights hang straight down without swinging or tilting; and no glare, motion blur, or cut interrupts the simultaneous clear view of both beams' free ends and their relative bending.

Scientific and Causal Correctness rubric:
level_1: Neither beam visibly bends; or a beam bends upward instead of downward; or the carbon fiber beam bends more than the aluminum beam; or both beams bend by the same visible amount; or bending appears before the weights are attached; or bending disappears after the weights are shown attached.
level_2: Both beams bend, but at least one of the following is wrong: the carbon fiber beam bends as much as or more than the aluminum beam; the bending starts before the weights are attached; the bending is sideways or twisting rather than straight downward; or the difference in how much each beam bends is too small to see.
level_3: Both beams bend downward once the weights are attached; the carbon fiber beam visibly bends less than the aluminum beam; the bending in both beams begins at the same moment the weights are attached and then holds steady, with no reversal, oscillation, or delayed onset.
level_4: Everything required at the 3-point level holds, and in addition: the gap between how much each beam bends stays visible for the whole observation period rather than narrowing or disappearing; and neither beam shows any sign of snapping, buckling, cracking, or changing color.
level_5: Everything required at the 4-point level holds, and in addition: the size of the bending gap tracks what stiffer material should look like (the carbon fiber beam keeps a noticeably straighter, gentler curve while the aluminum beam shows a visibly deeper, smoother curve), and neither beam shows any kink, sharp hinge-like bend, or other sign of permanent (plastic) deformation.

Spatiotemporal Consistency rubric:
level_1: One or both beams jump from one position to another with no visible bending motion connecting them; or a weight appears already attached to a beam's free end with no visible descent or attachment motion; or the room lighting or shadow pattern changes suddenly partway through the clip; or a beam's structure visibly breaks apart or vanishes mid-sequence; or the camera view pans, tilts, or zooms during the observation period.
level_2: At least one of the following happens: a weight's descent onto a beam's free end skips or stutters rather than moving continuously; the shadow cast by a beam or weight shifts position or orientation inconsistently over the course of the clip; the clamped end of a beam appears to flicker or change shape; or bright reflections on a beam's surface move in a way that doesn't match a single fixed light source.
level_3: Neither beam breaks apart or is affected by a camera viewpoint change; the shadows cast by the beams and weights keep a consistent direction and position throughout; each beam's geometry stays intact and only bends smoothly and continuously downward; and the weights' descent from release to rest is one unbroken motion for both beams.
level_4: Everything required at the 3-point level holds, and in addition: each beam's downward bend progresses smoothly from one moment to the next with no sudden jump or snap in curvature; both weights stay still once they've settled (no swinging, bouncing, or drifting); and there is no sudden lighting flicker, glare burst, or exposure change at any point.
level_5: Everything required at the 4-point level holds, and in addition: every visible stage of bending reads as a natural continuation of the moment before it, with the carbon fiber beam's shallower curve and the aluminum beam's deeper curve both progressing believably over time; and neither beam's outline shows ghosting, doubled edges, or smearing that would make its exact bent shape hard to judge at any moment.