Domain: Engineering — Mechanical Engineering
Target concept: Stress distribution

Video generation prompt: A uniform circular rod is horizontally fixed at one end (cantilever beam), and a vertical downward static load is applied at the free end. The load remains constant, with red representing tensile stress and blue representing compressive stress. The surface stress characteristics of the circular rod are displayed using red and blue.

Evaluation guide:
(i) Target concept: Elastic bending stress distribution in a statically loaded cantilever beam.
Minimum mechanism: The rod must behave as an isotropic, homogeneous, linear-elastic beam undergoing small deformations; fixed end imposes zero displacement and zero rotation; free end sustains only transverse force (no moment or axial load); stress sign reversal across neutral axis is mandatory.
(ii)Storyline: Frame 1: Static shot of horizontal uniform circular rod with one end visibly integrated into rigid support and opposite end suspended in empty space. Frame 2: Vertical downward arrow appears only at free end tip, no movement before/after. Frame 3: Rod begins smooth, monotonic downward bending with concave-down (hogging) curvature (the same curvature sense along the whole span that puts the top surface in tension) while the fixed end keeps zero slope. Frame 4: Red emerges exclusively on top hemisphere surface, blue emerges exclusively on bottom hemisphere surface, both expanding continuously from fixed end to free end. Frame 5: Final steady state: full bending curvature achieved; red and blue fully cover respective halves with sharp neutral axis; all elements remain static and co-registered. Perspective: Fixed frontal-side view (slight angle to reveal top/bottom surfaces), no camera motion, full rod in frame at all times.

Manual:
Experimental Procedure
1. Display a uniform circular rod, horizontally oriented.
2. Fix one end rigidly (e.g., clamped in a vise or embedded in solid base).
3. Leave the opposite end completely free (no support).
4. Apply a single static vertical downward load exclusively at the free end tip.
Observation of Experimental Phenomena
- Rod bends downward with concave-down (hogging) curvature, zero slope at fixed end, maximum displacement at free end.
- Top half of rod surface displays red color (tensile stress), most saturated near the fixed end and fading toward the free end.
- Bottom half of rod surface displays blue color (compressive stress), most saturated near the fixed end and fading toward the free end.
- Red and blue are sharply separated by a straight neutral axis running lengthwise.
Summary of Experimental Principles
In a cantilever beam under static end load, longitudinal fibers on the top surface elongate (tension → red), while those on the bottom surface shorten (compression → blue); the bending moment — and therefore the stress magnitude — is largest at the fixed end and decreases linearly to zero at the free end, so color intensity should visibly fade from fixed end to free end; stress distribution is linear through the depth of the rod, with zero stress along the neutral axis.

Prompt Grounding rubric:
level_1: No cantilever rod is visible at all, or no fixed/free end distinction can be made, or no downward load indicator appears at the free end, or no red/blue coloring appears anywhere on the rod's surface.
level_2: A rod-like object is present, but its support condition is ambiguous: it is not clearly fixed at one end while free at the other; a downward-pointing load indicator is present but not located at the free end tip; red and blue patches appear on the rod but are not mapped to distinguishable top/bottom regions of its surface.
level_3: A uniform circular rod is clearly shown: one end is rigidly fixed (e.g., embedded in a wall or clamped in a support) and the opposite end is completely free and unsupported; a single static downward-pointing load indicator sits only at the free end tip; red and blue regions appear on the rod's surface, but their layout does not clearly track top vs. bottom (e.g., red and blue are randomly scattered or layered in bands unrelated to top/bottom position).
level_4: All setup elements from the 3-point level are present and correctly arranged (uniform circular rod, horizontal orientation, one end visibly rigid and motionless, the opposite end fully unsupported, a single downward load indicator only at the free-end tip), and red and blue regions are broadly separated into top and bottom zones, but the split is imperfect (e.g., red crosses past the midline into the bottom half in places, or the blue region has gaps or discontinuities along the rod's length).
level_5: All setup elements are present, correctly arranged, and visually unambiguous: uniform circular rod held horizontal throughout; the fixed end is visibly immobile and rigidly mounted; the free end protrudes with no support of any kind; a single static downward load indicator appears only at the free-end tip and never moves; red covers the entire top half of the rod's surface along its full length and blue covers the entire bottom half, with no red/blue mixing, bleeding across the midline, or coloring appearing off the rod's surface.

Scientific and Causal Correctness rubric:
level_1: No meaningful cause-and-effect is shown between the applied load and the rod's response: e.g., the rod bends the wrong way (sagging/concave-up, as if the tip were pushed up rather than down), or red and blue are swapped (red on the bottom, blue on the top), or the rod shows no bending at all despite the load being present, or the coloring is unrelated to which surface is stretching versus compressing.
level_2: The rod bends and color appears, but the physics is self-contradictory: e.g., the rod bends downward with the correct hogging (concave-down) curvature yet red and blue are swapped, or the color mapping is correct (red top / blue bottom) but the curvature bends the wrong way (sagging/concave-up), or color appears on the surface before the rod shows any bending (violating cause-then-effect order), or the red/blue coloring is visibly stronger near the free end than the fixed end (the reverse of the correct pattern).
level_3: The rod bends downward with the correct concave-down (hogging) curvature throughout its length, and the color mapping is correct and consistent with that curvature: red only on the top surface (tension) and blue only on the bottom surface (compression); the load's appearance visibly precedes and drives the onset of bending and coloring; however, the red and blue coloring is uniformly saturated along the entire length of the rod, with no visible difference in intensity between the region near the fixed end and the region near the free end.
level_4: Everything in the 3-point description holds, and in addition the red and blue coloring is visibly more saturated near the fixed end and fades toward the free end, reflecting that bending stress is largest at the fixed end and decreases toward the free end; but the fade is not perfectly smooth (e.g., there is a visible plateau, a sudden step in intensity partway along the rod, or one small patch where the fade briefly reverses).
level_5: Everything in the 4-point description holds with a smooth, monotonic color-intensity gradient (red and blue are most saturated at the fixed end and fade continuously and without interruption to their faintest at the free end), and the entire causal sequence is physically coherent from start to end: the load appears first, the concave-down bending initiates at the fixed end and propagates outward, and the red/blue coloring builds in lockstep with the growing curvature at every point along the rod.

Spatiotemporal Consistency rubric:
level_1: The rod's continuity breaks at some point in the sequence: it disappears and reappears, or is visibly discontinuous; the fixed-end mount detaches, shifts, or rotates; the free end touches the ground or a support mid-sequence; the load indicator jumps to a new position or rotates; the red/blue coloring flashes on and off or vanishes and reappears; lighting or shadows change abruptly partway through the sequence.
level_2: The rod stays visible throughout, but shows a visible structural break: for example a gap or kink appears at the fixed-end mount, or partway along the rod's length; the bending curvature changes with a visible jump rather than smoothly; the red/blue regions shift position or blink without a matching change in the rod's actual curvature; the camera viewpoint rotates, zooms, or pans during the sequence.
level_3: The rod remains one continuous object throughout, rigidly fixed at one end and unsupported at the other; the load indicator stays fixed at the free-end tip without drifting; the red and blue regions stay attached to the rod's surface throughout without flashing or vanishing; bending progresses smoothly and monotonically from flat to fully curved; but one small spatiotemporal slip is visible, such as a brief stutter partway through the bending motion or a momentary gap between the red/blue boundary and the rod's actual surface at one point.
level_4: Everything in the 3-point description holds with no stutters: the rod's shape, the fixed-end mount, and the free-end clearance stay stable and coherent across the entire sequence; the load indicator never drifts from the free-end tip; the red/blue regions track the rod's surface exactly as it bends, with no visible lag or offset, except for one faint imperfection, such as the boundary between red and blue wavering slightly from moment to moment instead of staying a clean, stable line.
level_5: The entire sequence is free of spatiotemporal artifacts: the rod's shape and length stay physically consistent as it bends; the fixed-end mount never separates, shifts, or rotates; the free end stays clear of any surrounding object at all times; the load indicator stays motionless and centered exactly at the free-end tip; the red/blue boundary stays a clean, stable line that tracks the rod's surface continuously as the curvature develops, with no flicker, fading, or drift; lighting, shadows, and camera framing stay constant throughout, with no unexplained jump or shift.