Domain: Engineering — Materials Science & Engineering
Target concept: Bending along the visible grain direction vs. bending perpendicular to the visible grain direction

Video generation prompt: Place two identical wooden strips on supports: the grain of the left strip is aligned along the length, while the grain of the right strip is oriented transversely, and then apply the same downward bending force to both.

Evaluation guide:
(i) Target concept: Anisotropic mechanical response of orthotropic natural materials under bending load.
Minimum mechanism: Wood must possess aligned cellulose microfibrils forming directional grain; load must be applied in-plane and perpendicular to support span; deformation must reflect elastic bending governed jointly by the strips' cross-sectional second moment of area (a purely geometric property, identical for the two identically-sized strips) and their modulus of elasticity (which is grain-direction-dependent, higher along the grain than across it), so the visible stiffness difference comes from the wood's material anisotropy, not from any difference in cross-sectional shape.
(ii)Storyline: [Frame 0–2] Static setup: two strips placed side-by-side on supports, grain orientation clearly visible and correctly assigned. [Frame 3–4] Force initiation: identical force indicators begin moving vertically downward in unison toward center of each strip. [Frame 5–7] Force application & deformation: both strips sag downward; right strip exhibits greater continuous curvature progression than left strip, with no reversal or delay. [Frame 8–9] Steady state: force held constant; differential curvature is stable, visible, and fully resolved; grain texture remains coherent and undistorted. Perspective: fixed frontal orthographic or shallow-angle view ensuring full visibility of both strips, supports, grain direction, and deformation: no occlusion, no rotation, no zoom.

Manual:
Experimental Procedure
1. Place two identical wooden strips side-by-side on identical supports.
2. Orient left strip so visible grain runs parallel to its length; orient right strip so visible grain runs perpendicular to its length.
3. Apply identical downward force simultaneously to the center of each strip.
Observation of Experimental Phenomena
The right (transversely grained) strip bends more visibly downward than the left (longitudinally grained) strip.
Summary of Experimental Principles
Wood is anisotropic: bending stiffness is higher when force is applied parallel to grain direction and lower when applied perpendicular to grain direction.

Prompt Grounding rubric:
level_1: No wooden strips are shown, or only one strip appears, or the strip(s) are not resting on supports, or supports are missing, or no downward force is ever applied, or the grain direction cannot be told apart between the two strips (e.g., both look identical or no wood texture is visible at all).
level_2: Two wooden strips rest on supports, but something required is missing or wrong: the left strip's grain doesn't clearly run along its length, or the right strip's grain doesn't clearly run across it, or the same downward force is not applied to both (only one strip is pressed, or the two are pressed at different times or with visibly different force indicators).
level_3: Two matching wooden strips sit side by side on matching supports; the left strip's grain runs parallel to its long axis and the right strip's grain runs perpendicular to its long axis; a single downward force (finger, weight, or arrow) presses on the center of each strip at the same time; both strips stay fully visible and are not otherwise moved while the force is applied.
level_4: Everything required for score 3 is shown, and in addition the two strips sit at the same scale, same height, and same lighting side by side with nothing blocking either one, neither strip is rotated or moved between the initial setup and the force being applied, and the two supports match each other in shape and size and sit at mirrored positions under each strip.
level_5: Everything required for score 4 is shown, and in addition the force begins and ends at the same visible moment on both strips: if fingers press down, they press and hold together; if weights are dropped, they land and settle without one lagging behind the other; if arrows appear, they appear at the same time, with neither strip visibly starting to bend before the other.

Scientific and Causal Correctness rubric:
level_1: Neither strip shows any visible bending, or both strips bend by the same amount and in the same direction, or a strip bends before the force ever touches it, or a bend stays in the wood after the force is lifted away, or the grain directions shown are swapped from the prompt (transverse grain on the left strip, longitudinal on the right).
level_2: Only one of the two strips visibly bends, or the bending goes the wrong way (e.g., a strip arches upward instead of sagging under a downward push), or the grain is hard to read but the strip that ends up sagging more is the longitudinally-grained one rather than the transversely-grained one.
level_3: Both strips sag downward under the force, but the transversely-grained (right) strip visibly sags more than the longitudinally-grained (left) strip; the grain direction on each strip is clear enough to confirm which is which; the transversely-grained strip is never the stiffer-looking one of the pair.
level_4: Everything required for score 3 holds, and in addition the sag gap between the two strips grows steadily as the force is held: the transversely-grained strip's extra sag never briefly shrinks, and the longitudinally-grained strip never overtakes it in curvature at any point in the clip.
level_5: Everything required for score 4 holds, and in addition the bending only starts once the force indicator is actually touching the wood, keeps deepening while the force is held steady, and stops changing once the force stops changing (no bounce, no continued creeping, no springing back); neither strip shows twisting, splitting, or lifting off its supports beyond straightforward downward bending.

Spatiotemporal Consistency rubric:
level_1: A strip or support instantly appears in a different spot with no motion connecting the two positions, a support vanishes and comes back, the grain pattern flickers or switches direction partway through the clip, the force indicator jumps from one place to another with no path shown in between, or the overall lighting suddenly changes with nothing on screen to explain why.
level_2: A strip cracks or splits with no visible strain leading up to it, the wood grain pattern warps or rotates in a way that doesn't match the strip's shape, a support visibly squashes sideways even though it should be rigid, or the force indicator's motion skips, disappearing mid-path and reappearing farther along.
level_3: Both strips keep their shape, wood texture, and grain orientation throughout; the supports stay rigid and stay put; the force indicator moves along one continuous path down to the point where it touches the wood; neither strip disappears, blinks, or turns see-through at any point; and there is no sudden jump in the scene's overall brightness.
level_4: Everything required for score 3 holds, and in addition the grain pattern on each strip stretches or compresses smoothly as the wood bends rather than showing sudden warping, the visible curve of each strip grows outward from the point of contact toward the supports rather than appearing already fully curved, and the force indicator travels straight down at a steady pace without suddenly speeding up or pausing partway.
level_5: Everything required for score 4 holds, and in addition both strips' bending motion looks fully smooth with no visible skipping or stutter from frame to frame; the wood grain keeps a consistent look and contrast the whole time it bends; the shadow each strip casts changes shape in a way that plausibly follows its curve; and the camera never drifts or shifts in a way that changes where the two strips sit relative to each other.