Domain: Engineering — Mechanical Engineering
Target concept: Simply supported beam, with both ends resting on roller supports, subjected to a central load.

Video generation prompt: A straight beam is simply supported by two identical rollers; a concentrated load is gradually applied at the midpoint and then removed.

Evaluation guide:
(i) Target concept: Elastic bending of a statically determinate simply supported beam under a central point load.
Minimum mechanism: Beam must be isotropic, homogeneous, and behave linear-elastically; supports must constrain vertical translation only (roller condition); load must act purely perpendicular to beam axis at geometric center.
(ii)Storyline: [Frame 0–3] Beam rests straight on two identical rollers: endpoints in full contact, horizontal alignment visible. [Frame 4–6] Load descends vertically along centerline and makes contact at midpoint; beam begins smooth downward curvature peaking at center. [Frame 7–8] Load fully engaged: maximal symmetric deflection achieved; rollers unmoved; beam ends level. [Frame 9–10] Load ascends vertically along same centerline; beam curvature smoothly reduces. [Final frame] Beam fully restored to straight, horizontal, undistorted state; all objects retain original positions, shapes, and identities. Perspective: Fixed frontal/slightly elevated view showing full beam length, both rollers, and load path; no occlusion of midpoint or supports.

Manual:
Experimental Procedure
1. Place a straight rigid beam horizontally across two identical cylindrical rollers, one under each end.
2. Gradually lower a concentrated load onto the exact midpoint of the beam until visible downward deflection occurs.
3. Gradually lift the load away from the beam until it is fully removed and the beam returns to its original straight shape.
Observation of Experimental Phenomena
- Beam remains straight before loading.
- Beam deflects downward exclusively at midpoint during loading.
- Both ends stay fully supported by rollers throughout.
- Beam fully recovers to straight shape after load removal.
Summary of Experimental Principles
- Simply supported beam: ends rest freely on roller supports allowing rotation but no vertical displacement.
- Central concentrated load produces symmetric elastic deflection with maximum at midpoint.
- Deflection is fully reversible (elastic behavior) when load is removed.

Prompt Grounding rubric:
level_1: No simply supported beam visible; no two identical rollers present; no central load applied; no midpoint of beam identifiable; no load application or removal sequence shown.
level_2: Beam and two supports are present but not identifiable as identical rollers; beam is not straight or not oriented horizontally; load is applied but not at beam midpoint; no discernible load removal phase.
level_3: Straight horizontal beam rests on two visibly identical roller supports; a concentrated load is applied at the beam midpoint (visually centered); load removal occurs after application; all three core objects (beam, two rollers, load) are present and correctly positioned.
level_4: All conditions for score 3 satisfied AND beam remains visually continuous (no break or disconnection) throughout; rollers maintain fixed base contact with ground during entire sequence; load object maintains consistent shape and size before/during/after application; load appears only at midpoint (not elsewhere) during application phase.
level_5: All conditions for score 4 satisfied AND load object appears identically before application (held above midpoint), during application (in direct vertical contact with midpoint), and after removal (fully retracted to original height and position); beam endpoints remain fully supported by rollers at all times; no extraneous objects, labels, or overlays appear.

Scientific and Causal Correctness rubric:
level_1: Beam shows no deformation under load; or deforms without load; or deforms asymmetrically with only one support; or deflects upward; or shows permanent bending after load removal.
level_2: Beam deflects downward but not at midpoint (e.g., deflection peak offset); or deflection occurs without load being visibly in contact; or beam rebounds before load removal begins; or rollers visibly sink, rotate, or detach during loading.
level_3: Beam deflects downward exclusively at midpoint during load application; deflection disappears completely after load removal; beam returns to original straight shape; both rollers remain stationary and maintain full contact with beam ends throughout.
level_4: All conditions for score 3 satisfied AND beam curvature is smooth and symmetric about midpoint during loading; no kinks, buckles, or local folding observed; no residual sag or tilt remains after load removal; beam ends stay level and aligned with original horizontal orientation.
level_5: All conditions for score 4 satisfied AND deflection magnitude visibly increases continuously during load application (no jump or stutter), decreases continuously during removal (no snap-back or oscillation), and beam motion is strictly vertical at midpoint: no lateral shift, twist, or rotation of beam observed at any frame.

Spatiotemporal Consistency rubric:
level_1: Beam teleports, vanishes, or reappears mid-sequence; rollers change position or number abruptly; load jumps from off-screen to midpoint without visible motion path; lighting or shadow changes discontinuously between frames.
level_2: Beam exhibits unnatural stretching, shrinking, or warping; rollers slide laterally or lift off ground without causal motion; load object flickers, duplicates, or changes size inconsistently; camera viewpoint shifts (pan/tilt/zoom) or cuts to new angle.
level_3: Beam moves smoothly and continuously from undeformed → deflected → undeformed; rollers remain fixed in place with stable contact; load approaches midpoint along vertical path, contacts, then retracts vertically; no structural discontinuity (e.g., beam splitting, support detachment) or lighting/shadow jump observed.
level_4: All conditions for score 3 satisfied AND motion trajectories are physically coherent: load descent and ascent follow same vertical line; beam endpoints do not lift or drop relative to roller tops; no inter-frame strobing, ghosting, or motion blur that obscures object identity or state.
level_5: All conditions for score 4 satisfied AND temporal pacing is uniform: load movement speed appears constant during approach and retraction; beam deflection and recovery progress at matched visual rates; no frame duplication, missing frames, or temporal aliasing affecting continuity.