Domain: Engineering — Structural Engineering
Target concept: Wind generated by a fan was applied to high tower models with and without diagonal bracing: the unbraced tower swayed violently, tilted, and even collapsed; the braced tower remained almost stationary and maintained stability.

Video generation prompt: On the table, two tall model towers are placed side by side. The tower on the left is equipped with diagonal bracing, while the tower on the right is without diagonal bracing. An electric fan is positioned midway between the two towers, directing a continuous airflow of the same magnitude at both simultaneously. The wind intensity is gradually increased until noticeable swaying occurs in the model towers.

Evaluation guide:
(i) Target concept: Structural stability via triangulation under lateral (wind) loading.
Minimum mechanism: Towers must be slender, vertically oriented frameworks (not solid blocks); the diagonal bracing on one tower forms closed triangular subunits with its vertical and horizontal members; a single, steady wind source acts as a sustained horizontal force reaching both towers; the frame material is rigid enough that the braced tower resists visible deflection, while the unbraced tower is flexible enough to visibly deflect and, if the wind is sustained and grows strong enough, may progress from swaying to tilting or collapse, consistent with a quadrilateral frame's lack of shear resistance.
(ii)Storyline: Frame 0–2: Static setup. Two towers side-by-side on a table, fan off, diagonal bracing clearly visible on the left tower only. Frame 3–4: Fan is switched on. Blades begin turning, airflow starts reaching both towers. Frame 5–7: As wind intensity increases, the unbraced (right) tower begins visibly swaying side to side; the braced (left) tower shows no comparable movement. Frame 8–10: With continued wind, the unbraced tower's response may grow into visible tilting or collapse, while the braced tower remains essentially motionless throughout. Perspective: Fixed frontal, eye-level shot capturing the full height of both towers and the fan; no occlusion; a single, steady light casts shadows beneath the towers and fan base that do not shift direction during the shot.

Manual:
Experimental Procedure
1. Place two identical tall model towers side-by-side on a flat table.
2. Install diagonal bracing (X- or K-shaped members) on the left tower only; the right tower remains unbraced.
3. Position an electric fan midway between the two towers, aimed to blow airflow onto both simultaneously.
4. Turn on the fan and gradually increase wind intensity until swaying becomes visible.
Observation of Experimental Phenomena
- The unbraced tower sways laterally with increasing amplitude as wind intensity rises, and may progress to visible tilting or collapse under sustained strong wind.
- The braced tower remains rigid and stationary throughout, with no visible sway, tilt, or collapse at any wind intensity shown.
Summary of Experimental Principles
Diagonal bracing provides triangulation, converting the frame's unstable quadrilateral panels into stable triangles that resist lateral (shear) loads. Without this bracing, the frame can rack and eventually buckle or collapse under wind force; with bracing, the lateral load is transferred efficiently and the structure remains stable.

Prompt Grounding rubric:
level_1: Neither model tower nor the electric fan is visible; or the two towers are not placed next to each other on the table; or there is no sign of any airflow being directed at the towers; or the objects shown are unrecognizable as towers (wrong scale, abstract shapes, no lattice/frame structure at all).
level_2: Two tower-like structures appear but lack a clear vertical lattice framework with a base (e.g., solid blocks or vague silhouettes instead of rods); or the fan is present but is not aimed toward the towers; or the towers are arranged one behind the other or overlapping rather than side by side on the table.
level_3: Two tall lattice-style model towers stand side by side on a table; an electric fan is present and aimed toward the towers; diagonal bracing (visible X- or K-shaped rods running between the vertical and horizontal members) is present on one tower and absent on the other; the towers, fan, and table are all recognizable by their form and function.
level_4: All requirements of the 3-point level are met, AND the braced tower's diagonal rods are properly connected at both ends to the frame (not a loose rod merely resting against the structure); AND the unbraced tower shows no diagonal members anywhere on its frame; AND the fan is recognizably an electric fan (grille, motor housing, base, or cord) rather than a handheld or paper fan.
level_5: All requirements of the 4-point level are met, AND the two towers match in base size, height, and construction material/color, so that bracing is the only structural difference between them; AND the fan sits centered between the towers with airflow visibly reaching both sides equally (no tilt toward one tower over the other); AND no hands, tools, or other extraneous objects enter the frame at any point.

Scientific and Causal Correctness rubric:
level_1: Neither tower shows any lateral movement even though the fan is visibly blowing on them, or both towers sway by a similar visible amount; or the braced tower sways, tilts, or collapses while the unbraced tower stays still, reversing which tower should be the more stable one; or either tower moves while the fan is off.
level_2: Only one tower shows any response to the wind, but there is no clear contrast between the two towers' behavior (e.g., both remain equally still, or the response looks unrelated to the fan, such as motion appearing before the fan starts or after it stops).
level_3: The unbraced tower visibly sways side to side once the fan is on, while the braced tower shows no comparable lateral movement; both towers stay fully in view throughout; the swaying begins only after the fan starts blowing and grows as wind intensity increases.
level_4: All requirements of the 3-point level are met, AND the unbraced tower's sway visibly grows in amplitude as wind intensity increases, and if it progresses to visible tilting or collapse, this happens only to the unbraced tower and only after clearly preceding sway, not as a sudden, un-telegraphed break; AND the braced tower shows no comparable leaning, rotation, or joint give at any point, even as the unbraced tower's response intensifies.
level_5: All requirements of the 4-point level are met, AND the unbraced tower's motion (whether swaying, tilting, or eventual collapse) looks like a continuous, physically smooth response to increasing wind rather than an abrupt jump; AND the braced tower shows no perceptible lateral movement of its top relative to its base at any point, however strong the wind becomes; AND any eventual collapse involves only the unbraced tower's own members, with no debris or motion transferring to the braced tower.

Spatiotemporal Consistency rubric:
level_1: One of the towers or the fan vanishes from view and then reappears; a tower jumps to a different spot on the table between frames; the lighting suddenly changes brightness or direction with no visible cause; a tower's frame bends, stretches, or passes through the other tower; the camera cuts, pans, or zooms partway through the shot.
level_2: A tower or the fan disappears from view for a moment during the shot and then reappears; the fan's blades speed up, stop, or reverse with no visible cause; the table surface appears to shift or jump between frames; the shadows cast by the towers or fan swing to a new direction with no corresponding change in the light itself.
level_3: Both towers and the fan stay in the same spot on the table relative to each other throughout the shot; the fan's blades spin continuously without stopping or reversing; each tower's shape and joints look the same from frame to frame, with no rods appearing or disappearing; the shadows cast by the towers and fan point in one consistent direction for the whole sequence.
level_4: All requirements of the 3-point level are met, AND the camera does not pan, tilt, or zoom at any point; AND the diagonal bracing rods stay visibly attached at both ends across every frame, with no floating or detached-looking braces caused by perspective drift; AND the unbraced tower's sway follows a natural side-to-side arc rather than sliding sideways as a rigid block.
level_5: All requirements of the 4-point level are met, AND the unbraced tower's motion looks smooth from frame to frame, with no sudden freezing, skipping, or repeated poses; AND the fan's speed changes and the resulting change in the unbraced tower's sway happen close enough together that a viewer can tell the sway is responding to the fan, without a noticeable delay; AND the depth ordering stays correct throughout: the fan stays in front of the towers, the towers stay on the table, and nothing floats free of its surface.