Domain: Engineering — Structural Engineering
Target concept: Effect of Section Shape on Bending Behavior

Video generation prompt: Two steel beam models are placed side by side, each resting on two support stands positioned near its two ends so that its mid-span is elevated above the desk with open space beneath it. The left beam has an I-section, while the right one has a rectangular section. Both have the same cross-sectional area, and the same mid-span load is applied to both, causing them to deform. The difference in their deflection is compared.

Evaluation guide:
(i) Target concept: Bending stiffness depends on the sectional geometry (specifically the second moment of area, I), not just the material or the cross-sectional area.
Minimum mechanism: each beam must be supported only near its two ends (for example, on stands or blocks), leaving the mid-span section free to bend downward when loaded transversely; both beams must behave as linear-elastic, prismatic members; the I-section must have a higher second moment of area than the rectangular section of equal area because more of its material sits farther from the centroidal axis, in the flanges.
(ii) Storyline: Frame 1–2: static wide shot showing both beams resting on their end stands, their mid-spans clearly elevated above the desk, unloaded, with both cross-sections identifiable. Frame 3–4: load application. Identical loads appear simultaneously at mid-span on both beams, with no delay or stagger between them. Frame 5–9: progressive, smooth, synchronous downward bending. The I-section beam sags less (a shallower curve), the rectangular beam sags more (a deeper curve), each remaining symmetric about its mid-span. Frame 10: the deformed shape holds steady with no further change. Perspective: fixed frontal-oblique angle showing the full length of both beams, their end supports, both cross-sections, and the vertical load direction, with no occlusion of either beam or of the gap beneath their mid-spans.

Manual:
Experimental Procedure
1. Place two identical-length steel beams side by side, each resting on two support stands positioned near its two ends so the mid-span of each beam is elevated above the desk.
2. Left beam: I-section (flanges and web); right beam: solid rectangular section.
3. Ensure both beams have equal cross-sectional area (visually matched bulk).
4. Apply an identical downward load at the mid-span of each beam simultaneously.
Observation of Experimental Phenomena
The left (I-section) beam bends less, showing a shallower downward curve.
The right (rectangular) beam bends more, showing a deeper downward curve.
Summary of Experimental Principles
Supporting each beam only near its ends leaves the mid-span free to bend under a transverse load. I-sections concentrate material away from the neutral axis, in the flanges, which increases the second moment of area (I) and so reduces deflection under the same load compared with a rectangular section of equal area — demonstrating that section shape, not just material or area, governs bending stiffness.

Prompt Grounding rubric:
level_1: No two steel beam models are visible; or only one beam is present; or the beams are not placed side by side; or a beam rests flush along its entire length on the desk with no elevated gap beneath its mid-span, leaving no room to bend; or no mid-span load is applied to either beam; or the cross-section shapes cannot be told apart as I-section and rectangular.
level_2: Two beams are present and roughly side by side, but the support setup is wrong: for example, only one end of a beam is supported, the beams are propped at mismatched or random points, or there is no visible gap between the desk and either mid-span; or both beams show the same visible cross-section; or the load is applied off mid-span, or to only one beam, with no clear sign that the other received an equal load.
level_3: Two steel beam models sit side by side, each resting on two separate stands or blocks near its ends, with a clear gap between the desk and the mid-span of each beam; the left beam shows a visibly I-shaped cross-section with distinct flanges and a web; the right beam shows a visibly rectangular cross-section of uniform thickness; the same type of load (for example, an identical weight or a downward-force indicator) sits at the midpoint of each beam; nothing blocks the view of either beam's cross-section or its loading point.
level_4: Building on that baseline arrangement, both beams show matching visible bulk, with comparable overall height and width and no disproportionate scaling of one against the other; the end stands under each beam sit at matching distances from the beam's ends, so the two support arrangements mirror each other; the loads appear on both beams within a single frame of each other; and both beams stay in their resting positions throughout, aside from the bending itself.
level_5: Taking that further, both beams share the same surface color and finish, such as a matching metallic gray; no extraneous motion (vibration, sway, or camera jitter) occurs before, during, or after the load is applied; and the side-by-side alignment, the spacing of the support stands, and the gap beneath each mid-span all stay exactly as they started, with no shift, rotation, or occlusion at any point in the clip.

Scientific and Causal Correctness rubric:
level_1: Neither beam shows any downward deflection; or both beams deflect by the same amount and curvature despite their different cross-sections; or the I-section beam deflects more than the rectangular beam; or the visible deformation is not bending at all: for instance, the beam twists, buckles sideways, or merely compresses along its length.
level_2: Deflection shows up in only one beam while the other stays perfectly straight despite receiving the same load; or a beam curves before any load is shown touching it; or a beam curves upward under a downward load; or a beam's cross-section itself visibly crushes or fractures rather than the whole beam bending smoothly.
level_3: Once the load is applied, both beams sag downward at mid-span; the I-section (left) beam shows a visibly shallower, gentler curve than the rectangular (right) beam; both curves are smooth and roughly symmetric about the load point; and neither beam shows cracking, kinking, or any sign of permanent yielding.
level_4: Beyond that basic comparison, the gap between the I-beam's curvature and the rectangular beam's curvature widens smoothly as the load takes hold, never reversing or plateauing oddly partway through; and if the load is shown being lifted off, both beams spring back toward straight, while if the load stays on, neither beam keeps sagging further once it reaches its stable deflected shape.
level_5: At the highest level, the I-section beam's curve stays visibly shallower than the rectangular beam's curve at every point along the span, not just at mid-span; neither beam develops a kink or an asymmetric bulge anywhere along its length; and the deformation looks fully elastic, consistent with each beam simply bending under the load rather than being damaged by it.

Spatiotemporal Consistency rubric:
level_1: A beam's position or size changes discontinuously between frames: for instance, it jumps sideways on its stands or its length suddenly changes; a beam's cross-section flips between I-section and rectangular from one frame to the next; an abrupt, unexplained shift in lighting or shadow makes a beam hard to see; the load block disappears or reappears without ever being placed or lifted on screen; or a beam splits into disconnected pieces at any point.
level_2: A beam visibly slides along, or lifts off, its end stands by more than its own width with nothing shown to cause it; the load sitting on a beam changes size or shape while resting there; the gap beneath a beam's mid-span appears or disappears inconsistently between frames; or a beam's edges flicker between sharply defined and blurred in a way that breaks the sense of a single continuous object.
level_3: Both beams stay seated on their end stands in the same positions relative to each other and the desk for the whole clip; the applied loads stay in continuous contact with each beam's top surface at mid-span; small rendering imperfections may appear, such as a brief soft blur along a beam's edge as it bends, but nothing makes a beam appear to jump, lift off its supports, or swap its cross-section shape.
level_4: Building on that continuity, the camera's framing never shifts: no pan, tilt, or zoom; each beam's ends stay seated on their stands with no floating or gap opening up at the supports; and the bending motion of both beams reads as one continuous downward sweep rather than jumping between a few static-looking poses.
level_5: At the highest level of fidelity, motion reads as fluid from frame to frame for both beams, with no stutter or repeated frame; the depth ordering between the two beams and their supports never flips, so neither beam appears to pass through the other or through the desk; and once each beam reaches its final sagged shape, it holds steady with no further drift or wobble.