Domain: Natural Science — Physics
Target concept: Crumpled Paper versus Flat Paper Falling in Air

Video generation prompt: In a room, from the same height, a person simultaneously releases two identical sheets of paper, one tightly crumpled and the other kept flat, allowing them to fall side by side in still air.

Evaluation guide:
(i) Target concept: Differential air resistance as the dominant factor governing falling speed of identically massed objects with differing cross-sectional areas and drag coefficients in still air.
Minimum mechanism: Object must be low-mass, low-density, non-aerodynamic, so gravitational force is comparable to drag force; air must be still (no convection or drafts); release must be passive (no initial velocity); shape difference must be sufficient to produce visually resolvable descent rate divergence.
(ii)Storyline: [Frame 0] Both sheets held stationary, side-by-side, same height, distinct shapes visible (crumpled ball vs. flat rectangle). [Release onset] Simultaneous cessation of support: both begin downward motion in same frame. [Mid-descent] Crumpled sheet maintains compact shape and leads vertically; flat sheet exhibits gentle oscillation but lags, retaining planar form. [Landing sequence] Crumpled sheet contacts ground first; flat sheet remains airborne, continuing descent. [Visibility constraints] Fixed frontal viewpoint, full-body framing to capture release height and full descent path; no occlusion; lighting reveals shape details and motion trajectory.

Manual:
Experimental Procedure
1. Place two identical A4 paper sheets on a flat surface.
2. Crumple one sheet tightly into a compact ball with visible creases; leave the other fully flat and taut.
3. Hold both sheets at the same height, side-by-side, arms extended forward, palms horizontal.
4. Release both sheets simultaneously with no downward push.
Observation of Experimental Phenomena
The crumpled sheet falls rapidly and strikes the ground first; the flat sheet falls slowly, fluttering and remaining airborne longer, landing noticeably later.
Summary of Experimental Principles
Air resistance opposes motion more strongly on the flat sheet due to its larger surface area and lower density, slowing its descent. The crumpled sheet presents less surface area and higher effective density, reducing air resistance and allowing faster acceleration under gravity.

Prompt Grounding rubric:
level_1: No paper sheets are shown, or only one sheet appears; or neither sheet is clearly crumpled versus flat (e.g., both flat, both crumpled, or non-paper objects substituted); or the two sheets are not released from the same height; or the release is not simultaneous.
level_2: Two paper sheets are present and released, but a core requirement is broken: one sheet is only loosely balled or partly unfolded rather than tightly crumpled, or the 'flat' sheet is visibly bent, curled, or folded; or the two starting heights are clearly mismatched (one hand noticeably higher); or one sheet is released noticeably before the other; or the sheets start stacked or spaced far apart instead of side-by-side.
level_3: One sheet is clearly crumpled into a compact ball with visible creases and the other is clearly flat and taut; both start at the same height, side-by-side, and are released together, with the release and full descent staying within a fixed camera view; however, a distracting flaw is present, such as a releasing hand lingering in frame after letting go, a brief loss of framing right at release, or the two sheets briefly brushing against each other during the drop.
level_4: The crumpled and flat sheets are unmistakably distinct in shape, start level with each other, are released with no visible gap between when each leaves the hand, and stay side-by-side (not overlapping or swapping positions) for the whole visible fall; only small imperfections remain, such as a slight tremor in the releasing hand or a brief shadow flicker as a sheet passes a window/doorway light.
level_5: All 4-point conditions hold, and additionally: the crumpled sheet keeps its compact balled shape without unfolding, the flat sheet stays planar without curling into a tube or folding over itself, no hand or arm re-enters the frame after release, the camera framing does not cut or zoom at any point, and the two sheets remain visibly beside each other rather than converging, crossing paths, or swapping left/right position for the entire fall.

Scientific and Causal Correctness rubric:
level_1: The video contradicts the physics: the flat sheet reaches the ground before the crumpled sheet, or the two sheets fall at visibly the same rate, or the crumpled sheet floats or rises, or neither sheet shows net downward movement (e.g., only swaying or spinning in place).
level_2: The basic cause-and-effect breaks down: the crumpled sheet clearly descends but the flat sheet never net-descends (hovers, drifts sideways, or rises), or the flat sheet begins falling before the crumpled sheet, or the crumpled sheet's descent visibly slows or stalls while the flat sheet keeps accelerating, or the crumpled sheet unfolds into a flat shape mid-fall, erasing the shape difference the demonstration depends on.
level_3: The crumpled sheet is lower than the flat sheet at every comparable moment and reaches the floor first, and the flat sheet's descent is visibly slower throughout; however, a secondary flaw is present, such as the flat sheet fluttering or tumbling so much that its slower net descent is hard to track, or the crumpled sheet loosening partway through the fall (though it still lands first and stays clearly ahead the whole time).
level_4: The crumpled sheet is visibly ahead of (lower than) the flat sheet at every point after release and lands first; the flat sheet keeps a genuinely flat, planar shape while descending more slowly; the crumpled sheet keeps its compact balled shape; only a minor flaw remains, such as the flat sheet's edges fluttering while its overall orientation stays roughly horizontal, or the crumpled sheet turning slightly as it falls without opening up.
level_5: The crumpled sheet is ahead of the flat sheet at every visible moment from release to landing, with no point where the flat sheet catches up, passes, or lands first; the crumpled sheet keeps its dense, creased, balled shape and the flat sheet keeps its extended, planar shape throughout; the gap between the two sheets' fall progress never reverses; and the demonstration reads unambiguously as crumpling reducing air resistance so the balled sheet falls faster than the flat one.

Spatiotemporal Consistency rubric:
level_1: Either sheet visibly teleports (jumps position with no continuous path), vanishes or appears out of nowhere mid-fall, suddenly changes size or rotation with no cause, the shot cuts to a different framing, or a sheet passes through the floor or through the releasing hand.
level_2: A sheet blinks out and back in for a noticeable stretch, there is a visible splice or cut in the shot, the room lighting jumps abruptly (e.g., a shadow appears or disappears with no light source moving), a sheet stretches or warps into an unnatural shape, or a sheet tears or splits into pieces not part of the original setup.
level_3: No teleporting, cutting, or tearing occurs, and both sheets stay fully visible and side-by-side for the whole fall; however, a lesser flaw is present, such as a short stretch of motion blur that momentarily hides a sheet's shape, a faint shift in camera framing suggesting slight movement, or a shadow on the wall or floor that briefly looks inconsistent with where the sheets are.
level_4: There is no teleporting, no cuts, no tearing, and no sudden lighting jump; the crumpled sheet falls in a smooth, direct path and the flat sheet falls with a gentle wobble but no sudden jump or reversal in direction; the two sheets stay beside each other rather than crossing paths or swapping sides; only a small flaw remains, such as a brief blur right at the moment of release or a slightly unsteady background that does not affect the sheets themselves.
level_5: The whole fall reads as one continuous, physically coherent event: the crumpled sheet's path is steady and direct; the flat sheet's path shows only the mild, natural wobble expected from air resistance with no sudden direction reversal; the two sheets stay visibly side-by-side without drifting together, crossing, or swapping positions, with any lateral drift between them staying within roughly 10% of a sheet's width; any shadows they cast move smoothly and match the sheets' motion and orientation; and there is no moment where either sheet's speed appears to jump or reverse.